#
# 5 Aug 2005
#
# This file contains the grammatical errors found during the
# writing/review of the book "The New C Standard".
#
# The error is located on a line and delimited by $$. The
# characters between the first pair of $$ denote the words
# that were originally used ($$ means no words) and the
# characters between the second $$ are the words that should
# have been used ($$ means no words).
in those cases where exact details on the evaluation of an
expression is not required, a reader of the source will not have
$$to$
invest cognitive effort in reading and comprehending any explicit
conversion operations.
The first of these conventions has the potential for
$very$$
causing surprising behavior and is amenable to formulation as a
guideline recommendation.
Distinguishing between those cases where a size value is available
and when it is not
$$, is not$
always an easy task.
Use of parentheses makes the intentions of the developer clear
$$to$
all.
The blah comment form is
$something$sometimes$
used for "commenting out" source code.
However, in the context of an operand to the sizeof operator there is
an important
$different$difference$
in behavior.
The issues associated with it having a boolean role also
$applies$apply$
.
Most modern floating-point hardware
$$was$is$
based on the IEEE-754 (now IEC 60559) standard.
This limit is rarely reached
$in$$
except in automatically generated code. Even then it is rare.
The code that needs to be written to generate
$$this case$
is sufficiently obscure and unlikely to occur that no guideline
recommendation is given here.
Such usage is redundant
$$and$
does not affect the behavior of a program (the issue of redundant
code is discussed elsewhere).
If the guideline recommendation on a single integer types
$used$$
is followed any extended types will not be used.
What are the
$issued cause$issues caused$
by any deviations from this recommendation?
The performance of an
$$applications$
during certain parts of its execution is sometimes more important
than during other parts.
Developers are often told to break up complex
$$a$
statement or expression into several simpler ones.
Some languages (e.g., Ada, Java, PL/1) define statements
$$which$
can be used to control how exceptions and signals are to be handled.
While in other
$$cases$
the behavior is understood but the results are completely
unpredictable.
This issue
$also is$is also$
covered by a guideline discussed elsewhere.
Constraint and syntax violations are the only kinds of construct,
$by$$
defined by the standard, for which an implementation is required to
issue a diagnostic.
$It$If$
use is made of extensions, providing some form of documentation for
the usage can be a useful aid in estimating the cost of ports to new
platforms, in the future.
; or it
$use$uses$
some other implementation technique to handle this case (for
instance, if the segment used is part of a pointers representation a
special one part the end segment value might be
assigned).
External, non-processor based, interrupts are usually only
$be$$
processed once execution of the current instruction is complete.
Handling execution environment object storage limitations is
considered to be a design and algorithmic issue that
$$is$
outside the scope of these coding guidelines.
Given the support tools that
$a$are$
likely to be available to a developer, a limit on the nesting of
#include directives could provide a benefit by reducing developer
effort when browsing the source of various header files.
This requirement maintains the implicit assumption that use of one of
these identifiers should not cause
$to$$
any surprises.
The argument
$for$$
that many programs exhibit faults because of the unconstrained use of
objects at file scope, therefore use of parameters must be given
preference, is too narrowly focused.
Experience shows
$than$$
when writing programs developers often start out giving all objects
block scope.
It remains to be seen whether objects of type _Bool will be used in
contexts where such oversights,
$it$when$
made, will be significant.
An implementations choice of ``plain'' int also needs to consider the
affects
$$of$
how integer types with lower rank will be promoted.
$Is$Does$
a deviation from this guideline recommendation have a worthwhile
benefit?
However, no guideline recommendations are made because usage
$is$$
of complex types is not yet sufficiently great to warrant their
creation.
Almost at the drop of a hat objects
$$having$
an array type turn into a pointer to their first element.
A reader has
$$to$
balance goals (e.g., obtaining accurate information) and available
resources (e.g., time, cognitive resources such as prior experience,
and support tools such as editor search commands).
This constraint prevents source files
$cannot$
contain the UCN equivalent for any members of the basic source
character set.
However, the issue is not how many times a constant having a
particular semantic association occurs, but how many
$time$times$
the particular constant value occurs.
The majority of expressions
$are$$
contain a small number of operators and operands.
This technique
$is$$
essentially provides both storage and performance optimization.
Like C++, some other
$language$languages$
use the term rank.
Use of parentheses makes the intentions of the developer clear
$$to$
all.
These coding guidelines consider this to be a minor consideration in
the vast majority of cases and it is not given any weight
$by$$
in the formulation of the guidelines.
It is possible
$there$that$
the ordering of sequence points, during the evaluation of a full
expression, is non-unique.
The idea
$because$behind$
the cast operator is to convert values, not the types of objects.
No equivalent requirement
$$is$
stated for relational operators (and for certain operand values would
not hold[).
It is a moot point whether this requirement applies if both operands
have indeterminate values, since accessing either of
$the$them$
causes undefined behavior.
The standard
$specify$specifies$
how the store should be implemented.
While C++ supports the form (l = c) = i;, C does not
$does$$
.
The requirement
$on$that$
the result of pointer arithmetic still point within (or one past the
end) of the original object still apply.
Some languages (e.g., CHILL) provide a mechanism for specifying which
registers are to be used to hold objects (CHILL limits this
$$to$
the arguments and return value of functions).
Translator implementors are likely to assume that the reason a
developer
$providing$provides$
this hint is that they are expecting the translator to make use of it
to improve the performance of the generated machine code.
A common characteristic of some operations on tree structures is that
an access to an object, using a particular
$a$$
member name, is likely to be closely followed by another object,
using the same member name.
The Committee responses to defect reports (e.g., DR #017) asking
where the size of an object is needed
$did$do$
not provide a list of places.
A pointer to an incomplete structure or union type is a more strongly
typed
$from$form$
of generic pointer than a pointer to void.
The author of the source may intend
$to$$
a use of the const qualifier to imply a read-only object, and a
translator may treat it as such.
There is no requirement on translators to check that a particular
restricted pointer is the only method used
$access to$to access$
the pointed to object.
The size of all parameters in a function definition are required to
be known (i.e.,
$the$they$
have complete types), even if the parameter is only passed as an
argument in a call to another function.
Recognising
$the$that$
developers sometimes need to define functions that were passed
variable numbers of arguments the C Committee introduced the ellipsis
notation, in function prototypes.
An initializer enclosed in a brace pair
$are$is$
used to initialise the members of a contained subaggregate or union.
The continue and break statements are
$$a$
form of goto statement.
Looking at this grammar it can be seen that most terminals do not
match any syntax rules in the other parts of the
$languages$language$
.
An intentional usage may cause subsequent readers to
$more spend$spend more$
time deducing that the affect of the usage is to produce the value
zero, than if they had been able to find a definition that explicitly
specified a zero value.
The simplest way of adhering to a guideline recommending that all
identifiers appearing in the controlling expression of a conditional
inclusion directive
$$be defined$
is to insert the following (replacing X> by the undefined identifier)
on the lines before it:
A new header, ,
$was$has$
been defined for performing operations on objects having the type
_Complex.
This value
$will$$
is what is assigned to us, but first it has to be
converted, giving a value of 65535.
There
$are$was$
a big increase in numbers once drafts started to be sent out for
public review and meeting attendance increased to around 50-60 people.
$Meeting$Meetings$
occurred four times a year for six years and lasted a week (in the
early years meetings did not always last a week).
The C99 work was done at the ISO level, with the USA providing most
$$of$
the active committee membership.
Adding these numbers up
$give$gives$
a conservative total of 62 person years of effort, invested in the
C99 document.
During the early 1990s, the appropriate ISO procedure seemed to
$$be$
the one dealing with defects and it was decided to create a Defect
Report log (entries are commonly known as DRs).
It was agreed that the UK work item
$$would$
be taken out of the Amendment and converted into a series of DRs.
Many C++ translators offer a C compatibility mode, which
$is$$
often does little more than switch off support for a few C++
constructs.
The other advantage of breaking the translator into several
components is that it
$offered$offers$
a solution to the problem caused by a common host limitation.
However, many continue
$$to$
have internal structures designed when storage limitations were an
important issue.
(this usually means the amount
$$of$
storage occupied during program execution; which consists of machine
code instructions, some literal values, and object storage).
Some of the issues associated with generating optimal machine code
for various constructs are discussed
$with$$
in the sentences for those constructs.
There is sometimes a customer-driven requirement for programs to
execute within
$resources$resource$
constraints (execution time and memory being the most common
constrained resources).
Processor costs can be reduced by reducing chip pin-out (which
reduces the width of the data bus) and
$$by$
reducing the number of transistors used to build the processor.
To maximize locality of reference, translators need
$$to$
organize instructions in the order an executing program was most
likely to need them and allocate object storage so that accesses to
them always filled the cache with values that would be needed next.
The intent of these coding
$guideline$guidelines$
is to help management minimise the cost of ownership of the source
code they are responsible for.
The cost to the original developer may be small, but the cost to
subsequent developers (through requiring more effort by them
$$to$
work on code written that way) may not be so small.
Adhering to guidelines
$require$requires$
an investment, in the form of developers time.
Guidelines may be more
$of$or$
less costly to follow (in terms of modifying, or not using,
constructs once their lack of conformance to a guideline is known).
In this case the procedures followed are likely to be completely
different from those followed
$are$by$
paying customers.
While the impact of this form of production on
$tradition$traditional$
economic structures is widely thought to be significant , these guidelines still treat it as a form of production
(that has different cost/benefit cost drivers; whether the motivating
factors for individual developers are really any different is not
discussed here).
The culture of information technology appears
$$to be$
one of high staff turn over (with reported annual
turnover rates of 25-35% in Fortune 500 companies).
How to identify the components that might be reusable, how much
effort should be invested in writing the original source to make it
easy to reuse, how costs and benefits should be apportioned, are a
few of the
$question$questions$.
This program illustrates the often-seen situations of a program
behaving as expected because the input values used were not
sufficient to turn a fault
$into$in$
the source code into an application failure during program execution.
The
$effective$effect$
of different developer personalities is discussed elsewhere.
If it
$$is$
treated as an invisible implementation detail (i.e., the fact that C
is generated is irrelevant) then C guidelines do not apply (any more
than assembler guidelines apply to C translators that chose to
generate assembler, as an intermediate step, on the way to object
code). If the generated source is to be worked on by developers,
An attempt has been made to
$separated$separate$
out those guidelines that are probably best checked during code
review.
Unfortunately, few organizations invest the effort needed to write
technically meaningful or cost-effective guidelines, they then fail
$$to$
make any investment in enforcing them.
Unfortunately, few organizations invest the effort needed to write
technically meaningful or cost-effective guidelines, they then fail
to make any
$to$$
investment in enforcing them.
The availability of
$powerfully$powerful$
processors, coupled with large quantities of source code has changed
the modern (since the 1980s) emphasis to one of maintainability,
rather than efficiency.
Static analysis of code provides an estimate
$$of$
the number of potential faults, not all of these will result in
reported faults.
Could a pointer
$be$$
have the null pointer value in this expression?
Diffusion was calculated from the number of subsystems, modules, and
files modified during the change, plus the number of
$developer$developers$
involved in the work.
An idea initially proposed by Shneiderman ,
$whose$who$
proposed a 90-10 rule, a competent developer should be able to
reconstruct functionally 90% of a translation unit after 10 minutes
of study.
These sciences, and many engineering disciplines, have also been
$studies$studied$
experimentally for a long period of time.
However, here we are interested in the extent to which the results
obtained using such subjects
$$is$
applicable to how developers behave?
However, because of the lack of studies investigating this issue, it
is not yet possible to know
$that$what$
these programming ability factors might be.
There are a large number of developers
$$who$
did not study some form of computing degree at university, so the
fact that experimental subjects are often students taking other kinds
of courses is unlikely to be an issue.
The benefits of publishing negative results (i.e., ideas that did not
work)
$as$has$
been proposed by Prechelt.
There have also been specific proposals about how to
$for$$
reduce developer error rates, or improve developer performance.
Most commercial programs contain
$of$$
thousands of line of source code.
How do people estimate the likelihood
$$of$
an occurrence of an event?
This categorization process, based on past events, is a major factor
in the difficulty
$developer$developers$
have in comprehending old source.
$Object$Objects$
are grouped, relative to one another, based on some similarity metric.
How might two objects
$$be$
compared for similarity?
The reasons given
$by$$
for the Maya choices varied between the expert groups.
For instance, consumer research trying to predict how a shopper will
decide among packets of soap
$power$powder$
on a supermarket shelf.
The list of strategies discussed in the
$followed$following$
subsections is not exhaustive, but does cover many of the
decision-making strategies used when writing software.
For instance, some make trade-offs among the attributes of the
alternatives (making it possible for
$$an$
alternative with several good attributes to be selected instead of
the alternative whose only worthwhile attribute is excellent), while
others make no such trade-offs.
Compare each matching attribute in the two
$alternative$alternatives$
.
People can behave differently, depending
$in$on$
whether they are asked to make a judgment, or a choice.
People can behave differently, depending on whether
$that$they$
are asked to make a judgment, or a choice.
These three
$alternative$alternatives$
can be grouped into a natural hierarchy, depending on the requirements.
Once this initial choice has been made other attributes can be
considered (since both
$alternative$alternatives$
have the same efficiency).
Code written using flow is not recommended, and
$$is$
not discussed further.
Because they stand out,
$the$$
developers can easily see what changes were made to their code, and
decide what to do about them.
Because they stand out, developers can easily
$seen$see$
what changes were made to their code, and decide what to do about them.
Once they had seen the question, and answered it, subjects were able
to accurately
$calibrated$calibrate$
their performance.
$The$They$
learn the implicit information that is not written down in the text
books.
$Developer$Developers$
generally believe that any difficulty others experience in
comprehending their code, is not caused by how they wrote it.
While developers know that time limits will make it very unlikely
that they will have to justify every decision, they do not know in
$advantage$advance$
which decisions will have to be justified. In effect the developer
will feel the need to be able to justify most decisions.
A task having intuition-inducing characteristics is most likely to be
carried
$$out$
using intuition, and similarly for analytic-inducing characteristics.
Studies of the backgrounds of
$recognise$recognised$
experts, in many fields, found that the elapsed time between them
starting out and carrying out their best work was at least 10 years,
often with several hours deliberate practice every day of the year.
Does an initial aptitude or interest in a subject lead to praise from
others (the path to musical and chess expert performance often starts
in childhood), which creates the atmosphere for learning, or are
$others$other$
issues involved?
The results showed that subjects made rapid improvements in some
areas (and little thereafter), extended practice produced continuing
$improvements$improvement$
in some of the task components, subjects acquired the ability to
perform some secondary tasks in parallel, and transfer of skills to
new digital circuits was substantial but less than perfect.
It is not the intent of this book to decry the general lack of good
software development training, but simply to point out that many
developers have not
$have$had$
the opportunity to acquire good habits, making the use of coding
guidelines even more essential.
Nisbett and Norenzayan provide
$and$an$
overview of culture and cognition.
Whether 25 years is sufficient
$to$for$
a programming language to achieve the status of being established, as
measured by other domains, is an open question.
Given this situation we would not expect to find large
$performances$performance$
differences in software developers, through training.
Your author can often tell if a developer's previous
$languages$language$
was Fortran, Pascal, or Basic.
There is evidence to suggest that some of these
$so-call$so-called$
cognitive limitations provide near optimal solutions for some real
world problems.
To travel from the
$font$front$
of the brain to the rear of the brain requires at least 100 synaptic
operations, to propagate the signal.
During recall a person attempts to use information immediately
available to them to access other information held
$their$in$
memory.
Recent research on working memory has
$began$begun$
to question whether it does have a capacity limit.
(number items at which chunking becomes more efficient
$that$than$
a single list, 5-7).
Until recently experimental studies of memory
$has$have$
been dominated by a quantity oriented approach.
(one of which was in the set
$$of$
640 pictures seen earlier).
For instance, a driver returning to a car wants to know where it was
last parked, not the
$locations$location$
of all previous places where it was parked.
The third row
$indicated$indicates$
learning performance, the fifth row recall performance, relative to
that of the control.
A task is usually comprised of several goals
$then$that$
need to be achieved.
As they gain experience they learn specific
$solution$solutions
to specific problems.
(
$an$in$
domains where poor performance in handling interruptions can have
fatal consequences)
Those errors that occur during execution of an
$actions$action$
are called slips and those that occur because of an error in memory
are called lapses.
People adopt a variety of strategies, or heuristics, to overcome
limitations in the cognitive resources available to
$then$them$
, to perform a task.
These errors are often claimed, by the author, to be caused
$$by$
any one of any number of factors, except poor reasoning ability.
For some time a few economists have been arguing that people do not
behave according to
$mathematically$mathematical$
norms, even when making decisions that will affect their financial
well being.
This problem is framed in terms of 600 people
$dieing$dying$
, with the option being between two programs that save lives.
The most representative value might be the mean for all the
$function$functions$
in a program, or all the functions written by one author.
Statistically this is not true, the sequences HHHHHHHHHH and
THHTHTTHTH are equally
$probably$probable$
, but one of them does not appear to be representative of a random
sequence.
(based
$of$on$
beliefs that have similar meanings)
The results suggested that their subjects always believed an
assertion presented to them, and that only once they had comprehended
it
$where$were$
they in a position to, possibly, unbelieve it.
This finding has
$implication$implications$
for program comprehension in that developers sometimes only glance at
code.
Karl Popper pointed out that scientific theories could never be
$$shown$
to be logically true, by generalising from confirming instances.
What test strategy
$$is$
the best approach during program comprehension?
It might be thought that reasoning ability declines with age, along
with other
$the$$
faculties.
How could adding the alternative chocolate ice cream
$possible$possibly$
cause a person who previously selected vanilla to now choose
strawberry?
(i.e., should a guideline recommendation be made rather than what
recommendation
$night$might$
be made)
Usage subsections is that the former are often dynamic (instruction
counts from executing programs), while the
$later$latter$
are often static (counts based on some representation of the source
code).
$screened$screen$
based interactive applications often contain many calls to GUI
library functions and can spend more time in these functions than the
developers code.
Some applications consist of a single, monolithic, program, while
others
$$are$
built from a collection of smaller programs sharing data with one
another.
Nevertheless, a collection of
$program$programs$
was selected for measurement, and the results included in this book.
The Committee preferred to consider the extent of usage in existing
programs and only
$become$became$
involved in the characteristics of implementations when there was
wide spread usage of a particular construct.
An
$implementations$implementation$
may be required to select among several alternatives (these form the
category of unspecified behaviors), chose its own behavior (these
form the category of implementation defined behaviors), or the
standard may not impose any requirements on the behavior (these form
the category of undefined behaviors).
In applications where code size is more important
$that$than$
performance it can be the deciding factor in choosing an interpretive
approach.
Whether use of an option radically
$change$changes$
the behavior of a translator or has no noticeable affect on the
external output of the generated program image is outside the
scope of these coding guidelines.
Whether use of an option radically changes the behavior of a
translator or has no noticeable affect on the external output of the
generated program image
$it$$
is outside the scope of these coding guidelines.
In practice usage of particular wording in the standard may be
incidental, or the developer
$$may$
not have read the wording closely at all.
It typically seems to take around five years to produce
$$and$
revise a language standard.
However, the first priority should always be to make sure that the
guideline recommendations are followed, not inventing new procedures
to
$handling$handle$
their change control.
At the time of writing WG14 has decided to wait until the various
dark corners have been more fully investigated and the
$issued$issues$
resolved and documented before making a decision on the form of
publication.
The keyword &uu;attribute&uu; can be
$use$used$
to specify an objects alignment at the point of definition:
There are a some undefined behaviors that give consistent
$$results$
on many processors.
The 64 possible codons are used to represent different amino acids,
$what$which$
are used to make proteins, plus a representation for stop.
(an important consideration if
$perform$performing$
relational operations on those addresses)
The visible appearance
$$of$
a character when it is displayed is called a glyph.
For instance, should the call printf("%.0f", 2.5) produce the same
$a$$
correctly rounded result as the value stored in an equivalent
assignment expression?
Market forces usually dictate that the quality of most implementation
diagnostic messages
$$be$
more informative.
This C
$sentences$sentence$
brings us onto the use of ISO terminology and the history of the C
Standard.
On the whole the Committee
$do$does$
not seem to have made any obvious omissions of definitions of behavior.
Pointing out
$$that$
the C Standard does not always fully define a construct may undermine
developers confidence in it.
A strictly conforming program is intended to be maximally portable
$that$and$
can be translated and executed by any conforming implementation.
As
$previous$previously$
discussed, this is completely unrealistic for unspecified behavior.
Most formal validation
$concentrate$concentrates$
on the language syntax and semantics.
All
$function$functions$
containing an occurrence of an extension contain a comment at the
head of the function definition listing the extensions used.
The majority of real
$program$programs$
being translated by an extant implementation at some point.
In some cases this terminology
$refer$refers$
to a more restricted set of functionality than a complete execution
environment.
$Other$Others$
have a very laid-back approach.
Most languages do not contain a preprocessor, and do not need to
$specify$$
go to the trouble of explicitly calling out phases of translation.
Many languages are designed with an Ascii character set in mind, or
do not contain a sufficient number of punctuators and operators that
all characters
$non$not$
in a commonly available subset need to be used. Pascal specifies
what it calls lexical alternatives for some lexical tokens.
Both quality of implementation issues
$$are$
outside the scope of the standard.
This can occur when source
$file$files$
are ported.
The base document was not clear on this subject and some implementors
interpreted
$$it$
as defining a character preprocessor.
Probably the most
$common$commonly$
used conversion uses the values specified in the Ascii character set.
Differences between the values of character set members in the
translation and execution environments become visible if
$there$$
a relationship exists between two expressions.
A preprocessing token that cannot be converted to a token is likely
$will$to$
cause a diagnostic to be issued.
Linking is often an invisible part of
$build$building$
the program image.
In the case of incorrect objects, things might appear
$$to$
work as expected.
(a
$simply$simple$
compression program was included with each system)
Provided the sequence being replaced
$in$is$
larger than the substituted call instruction the program image will
shrink in size.
An implementation may choose to convert all
$sources$source$
characters.
Constraint violations during preprocessing can be difficult to
localize because of the unstructured
$natured$nature$
of what needs to be done.
The action taken, if any, in those cases where the use is not
diagnosed will depend on the cost of independent checking of the
source (via some other tool, even a C translator) and the benefit
$of$$
obtained.
Just because control has been returned to the execution environment
does not mean that all visible
$the$$
side effects of executing that program are complete.
Information may be
$past$passed$
into the function called.
$Traditional$Traditionally
there is a small bootstrap loader at this location.
(it might be a
$simply$simple$
operating system)
Most hosted
$environment$environments$
provide the full set of functionality specified here.
One syntax, or constraint violation, may result in diagnostic
$message$messages$
being generated for tokens close to the original violation.
Some translators support an option that causes any usage of an
extension,
$provide$provided$
by the implementation, to be diagnosed.
(lint being the fluff-like material that clings to clothes and
$find$finds$
its way into cracks and crevices)
There is a possibility that one of the character
$sequence$sequences$
in one of the strings pointed to by argv will be
truncated.
The space character
$$is$
treated as the delimiter.
They contain additional language constructs at each
$levels$level$
.
Such operations only become noticeable if there
$is$are$
insufficient resources to satisfy them.
(and nearly every
$of$$
commercially written program, irrespective of language used)
There have been proposals for detecting, in hardware, common
subexpression evaluations during program execution and reusing
$previous$previously$
computed results.
It is source
$could$code$
that developers do not need to read.
For instance, in the case of unused storage, execution performance
can be
$affect$affected$
through its effect on cache behavior.
The most
$common$commonly$
seen levels of analysis operate at the function and statement level.
In practice, given current tool limitations,and theoretical problems
associated with incomplete information, it is unlikely that all dead
$$code$
will be detected.
The workings of the abstract machine between the user issuing the
command to execute a program image and the termination of that
program is unknown to the outside
$word$world$
.
(in some
$language$languages$
that support a model of parallel execution, the order of some
statement executions is indeterminate)
Normally a translator would have the
$options$option$
of keeping the value of this calculation in a register, or loading it
from x.
The setting of the status flags and control modes defined in IEC
60559
$represent$represents$
information about the past and future execution of a program.
Floating-point operations are a
$technical$technically$
complex subject.
Apart from the general exhortation to developers to be careful and to
make sure they know what they are doing, there is little of practical
use
$they$that$
can be recommended.
Checking status flags after every floating-point
$operations$operation$
usually incurs a significant performance penalty.
There can be a significant performance penalty associated with
$continual$continually$
opening and closing streams.
These having been zero filled or sign extended, if necessary, when
the value was
$load$loaded$
from storage, irrespective of the size of the value loaded.
The original rationale of such a design is that instructions
operating on smaller ranges of values could be made to
$executed$execute$
faster than those operating on larger ranges.
This locale usually requires support for extended characters in the
form of those
$member$members$
in the Ascii character set that are not in the basic source character
set.
Null characters are different from other escape sequences in a string
literal in that
$$they$
have the special status of acting as a terminator.
The Committee realized that a large number of existing
$program$programs$
depended on this statement being true.
Some
$mainframe$mainframes$
implement a form of text files that mimic punched cards, by having
fixed-length lines.
Like C, most language implementations
$them$$
support additional characters in string literals and comments.
A study by Waite found 41% of total translation time was spent in a
$handcraft$handcrafted$
lexer.
Such a change of locale can alter how multibyte characters are
interpreted by
$$a$
library function.
This is a set of
$requirement$requirements$
that applies to an implementation.
(generating any escape sequences and the appropriate
$bytes$byte$
values for the extended character selected by the developer)
When trigraphs are used, it is possible to write C source code that
contains only those characters that are in
$$the$
Invariant Code Set of ISO/IEC 646.
The fact that many multibyte sequences are created automatically, by
an editor, can make it very
$difficulty$difficult$
for a developer to meet this requirement.
The developer
$$is$
relying on the translator ignoring them.
Any developer
$that$who$
is concerned with the direction of writing will require a deeper
involvement with this topic than the material covered by the C
Standard.
On other display devices, a fixed amount of storage is allocated for
the characters that may occur on each line
$occupies$$
.
The standard does not specify how many horizontal tabulation
positions must be supported by an implementation,
$is$if$
any.
Requiring that any developer-written functions to be callable from a
signal handler restricts the calling conventions that may be used in
such a handler to
$being$be$
compatible with the general conventions used by an implementation.
(the
$actually$actual$
storage allocation could use a real stack or simulate one using
allocated storage)
But within these coding guidelines we are not just interested in
translator limitations, we
$$are$
also interested in developer limitations.
It is also important to consider
$$the$
bigger picture of particular nested constructs.
Nesting of blocks is part of the language syntax and
$$is$
usually implemented with a table driven syntax analyser.
Many others use a dynamic data structure relevant to the
$being type$type being$
defined.
Although some uses of parentheses may be technically redundant, they
may be used to simplify the visual appearance
$or$of$
an expression.
The extent to which these will be increased to support
$new the$the new$
C99 limit is not known.
The extent to which these will be increased to support the new C99
limit
$$is$
not known.
This
$limits$limit$
matches the corresponding minimum limits for size_t and ptrdiff_t.
However, even
$$if$
a declaration occurs in block scope it is likely that any internal
table limits will not be exceeded.
Given the typical source code
$indentations$indentation$
strategies used for nested definitions it is likely that deeply
nested definitions will cause the same layout problems as deeply
nested blocks.
Such an expectation
$increase$increases$
search costs.
The editing effort will be proportional to the number of occurrences
of the moved members in the existing code, which
$require$requires$
the appropriate additional member selection operation to be added.
The character type use two's complement notation and
$occupy$occupies$
a single byte.
The contexts in which these identifiers (usually macros) might be
expected to occur
$is$are$
discussed in subsections associated with the C sentence that
specifies them.
In the first function
$assumes$assume$
a byte contains eight bits.
(perhaps suggesting that CHAR_MIN always be
$case$cast$
to type int, or that it not appear as the operand of a relational
operator).
The difference in value between the smallest representable normalized
number closest to zero and zero is much larger than the
$different$difference$
between the last two smallest adjacent representable normalized
numbers.
The infinity values (positive and negative) are not a finite
floating-point
$values$value$
.
This wording
$as$was$
added by the response to DR #218, which also added the following
wording to the Rationale.
A percentage change in a value
$if$is$
often a more important consideration that its absolute change.
The error in ulps depends on the radix and the precision used
$the in$in the$
representation of a floating-point number, but not the exponent.
This provides floating-point operations to a known, high level of
accuracy, but
$some what$somewhat$
slowly.
The IEC 60559 Standard
$not only$also$
allows implementations latitude in how some constructs are performed.
This is how translators are affected by
$how$$
the original K&R behavior.
This is how translators
$$are$
affected by the original K&R behavior.
Few other languages get involved in exposing such
$detailed$details$
to the developer.
When the least significant double has a value of zero, the
$different$difference$
can be very large.
The external effect is
$$the$
same.
Space can be saved by writing out fewer than DECIMAL_DIG digits,
provided the floating-point value contains less precision
$that$than$
the widest supported floating type.
The usage of these macros in existing code is so rare that
$it$$
reliable information on incorrect usage is not available.
Many implementations use a suffix to give the value
$the$a$
type corresponding to what the macro represents.
Many implementations use a suffix to give the value a type
corresponding to
$the$$
what the macro represents.
How many
$calculation$calculations$
ever produce a value that is anywhere near as small as FLT_MIN?
The availability of parser generators is an incentive to try
$and$to$
ensure that the syntax is, or can be, rewritten in LALR(1) form.
Most
$simple$simply$
state that the labels are visible within the function that defines
them, although a few give labels block scope.
Most functions are not recursive, so separate objects for nested
invocations
$$of$
a function are not usually necessary.
Where the scope of an
$identifiers$identifier$
begins is defined elsewhere.
A tag name may
$$be$
visible, but denoting what is known as an incomplete type.
This design choice can make it difficult for
$$a$
translator to operate in a single pass.
$It$In$
many cases it mirrors an object's scope and developers sometimes use
the term scope when lifetime would have been the correct term to use.
In many cases it mirrors an object's scope and developers sometimes
use the term scope when lifetime would have been
$be$$
the correct term to use.
An implementation that performs garbage collection may have one
$characteristics$characteristic$
that is visible to the developer.
In other words, is there an opportunity for a
translator to
$reused$reuse$
the same storage for different objects?
However, discussion of techniques for controlling a
$program$program's$
use of storage is outside the scope of this book.
It is safer to let the translator perform the housekeeping needed to
handle such shared storage than to try
$and$to$
do it manually.
This behavior is common to nearly every block scoped
$languages$language$
.
C does not define any
$out-or-storage$out-of-storage$
signals and is silent on the behavior if the implementation cannot
satisfy the requested amount of storage.
This
$is$$
value is needed for index calculations and is not known at
translation time.
The C++ Standard does not go into this level of
$details$detail$
.
So an integer constant is not simpler
$that$than$
an identifier.
The aim of these C++ subclauses is to
$pointed$point$
out such sentences where they occur.
However, they don't usually get
$involve$involved$
in specifying representation details.
Several implementations include
$$support$
for the type specifier bit, which enables objects to be declared that
denote specific bits in this data area.
While the
$later$letter$
avoids subtle problems with different representations of the two
values used in the representation.
The Committee
$ recognize$ recognized$
that new processors are constantly being developed, to fill niche
markets.
The amount of storage occupied by the two types may be the same, but
they are different types and may
$$be$
capable of representing different ranges of values.
The migration to processors where 64-bit integers are the natural
architectural choice
$is$$
has only just started (in 2002).
Treating it as a distinct type reinforces the developer expectation
that implementations will treat it
$is$as$
purely a boolean type, having one of two values.
Following guidelines
$are$is$
unlikely to have precedence in these cases, and nothing more is said
about the issue.
The typedef intmax_t was introduced to provide a name for the concept
of widest integer type to prevent this issue from causing a problem
in
$$the$
future.
This requirement
$ensure$ensures$
that such a conversion does not lead to any surprises, if the operand
with signed type is positive.
This specification describes the behavior of arithmetic operations
for the vast majority
$$of$
existing processors operating on values having unsigned types.
However, mathematicians working in the field of program correctness
often frown on reliance
$of$on$
modulo arithmetic operations in programs.
(unlike
$other many$many other$
languages, which treat members as belonging to their own unique type)
Resnick describes a measure of semantic similarity
$base$based$
on the is-a taxonomy that is based on the idea of shared information
content.
Adding or removing one member should not affect the presence
$or$of$
any other member.
Languages that contain enumerated types usually
$treat also$also treat$
them as different types.
The names of the members also
$providing$provide$
a useful aid to remembering what is being represented.
For example, it may simply indicate that padding between members is
to be minimized, or it may take additional tokens
$specifying$specify$
the alignments to use.
The reason for defining a member as being part of a larger whole
rather than an independent object is that it has some form of
association with
$other$$
the other members of a structure type.
If three different types are defined, it is necessary to
$have$$
define three functions, each using a different parameter type.
(one of whose
$purpose$purposes$
is to hide details of the underlying type)
Some languages do allow references to function types
$$to$
be passed as arguments in function calls.
Apart from the occasional surprise, this incorrect assumption does
$do$$
not appear to have any undesirable consequences.
Apart from the occasional surprise, this incorrect assumption does
not appear to
$be$have$
any undesirable consequences.
Nearly
$ever$every$
implementation known to your author represents a reference using the
address of the referenced object only.
It is rarely heard
$in$$
outside of the committee and compiler writer discussions.
This terminology is not commonly used outside of the C Standard and
its unfamiliarity, to developers, means
$it$$
there is little to be gained by using it in coding guideline
documents.
Unqualified types are much more commonly used
$that$than$
qualified types.
Code that
$make$makes$
use of representation information leaves itself open to several
possible additional costs:
Code that makes use of representation information
$leave$leaves$
itself open to several possible additional costs:
The ordering of bytes within an object containing more than one of
them is not specified, and there
$$is$
no way for a strictly conforming program can obtain this information.
The term object usually has
$very a$a very$
different meaning in object-oriented languages.
A processor may
$places$place$
restrictions on what storage locations can be addressed.
If a pointer to character type is used to copy all of the bits in an
object to another object, the transfer will
$is$be$
performed a byte at a time.
For padding bytes to play a part in the choice of algorithm used to
make the copy
$they$there$
would have to be a significant percentage of the number of bytes
needing to be copied.
In the former case it can copy the member assigned to, while in the
$later$latter$
case it has to assume that the largest member is the one that has to
be copied.
$You$Your$
author does not know of any processor supporting such instructions
and a trap representation.
Segmented architectures did
$no$not$
die with the introduction of the Pentium.
Given
$the$that$
C does not contain support for objects having structure or union
types as operands of the equality operators, use of memcmp has some
attractions.
This occurs for integer types represented in one's complement and
signed magnitude format, or the floating-point representation
$is$in$
IEC 60559.
However, implementations of these languages will target
$execute$$
the same hosts as C implementations.
It is possible for two types to be compatible when their types are
not
$$the$
same type.
There is never
$any$an$
issue of other structure types, containing members using the same
set of names, influencing other types.
The C90 Standard is lax in not
$explicit$explicitly$
specifying that the members with the same names have the same values.
This can cause some inconsistencies in the display of enumeration
constants, but debuggers are outside
$of$$
the scope of the standard.
Linkers supporting
$support$$
C++ usually contain some cross translation unit checks on function
types.
There are two main lines of thinking about binary operators whose
$on$$
operands have different types.
The other is to
$be$$
have the language define implicit conversions, allowing a wide range
of differing types to be operated on together.
The commonly
$term$$
used developer term for implicit conversion is the term implicit cast.
These differences, and the resulting behavior,
$is$are$
sufficient to want to draw attention to the fact that a conversion is
taking place.
This does not imply that the object representation of the type _Bool
contains a smaller
$numbers$number$
of bits than any other integer type.
The type char is usually a separate type and an explicit conversion
is needed if an operand
$$of$
this type is required in an int context.
The type used in a bit-field declaration specifies the set of
possible values that might be available,
$from$$
while the constant value selects the subset that can be represented
by the member.
The type used in a bit-field declaration specifies the set of
possible values that might be available, while the constant value
selects the subset
$than$that$
can be represented by the member.
This can involve using a bitwise and instruction to zero out bits and
right
$shifting$shift$
the bit sequence.
Some CISC processors have instructions specifically designed to
$accessing$access$
bit-fields.
Type conversions occur at translation time,
$where$when$
actual values are usually unknown.
The integer promotions are only applied to values whose integer type
has a rank
$is$$
less than that of the int type.
Value preserving rules can also
$product$produce$
results that are unexpected, but these occur much less often.
This general statement
$that$$
holds true for conversions in other languages.
(although this is a
$commonly$common$
developer way of thinking about the process)
A promotion would not affect the outcome in these contexts, and an
implementation can use the as-if rule in selecting the best machine
code to
$generating$generate$
.
Many other language standards were written in an age
$where$when$
floating-point types could always represent much larger values than
could be represented in integer types.
A
$simply$simple$
calculation would suggest that unless an implementation uses the same
representation for floating-point types, the statistical likelihood
of a demoted value being exactly representable in the new type would
be very low.
A simple calculation would suggest that unless an implementation uses
the same representation for floating-point types, the
$statistically$statistical$
likelihood of a demoted value being exactly representable in the new
type would be very low.
For very small values there is always a higher and lower value that
bound
$it$them$
.
Support for complex types is new in C99 and there is no experience
based on existing usage
$it$$
to draw on.
Some languages support implicit conversions while
$other$others$
require an explicit call to a conversion function.
$Invariable$Invariably$
the type that can represent the widest range of values tends to be
chosen.
On some processors arithmetic operations can
$produces$produce$
a result that is wider than the original operands.
As well
$$as$
saving the execution time overhead on the conversion and additional
work for the operator, this behavior helps prevent some unexpected
results from occurring.
A universal feature of strongly typed languages is that the
assignment operator is only
$being$$
able to store a value into an object that is representable in an
objects declared type.
$Language$Languages$
that support operators that can modify the value of an object, other
than by assignment, sometimes define a term that serves a purpose
similar to modifiable lvalue.
As the standard points out elsewhere, an incomplete type may only
$by$be$
used when the size of an object of that type is not needed.
In the following, all the function calls are
$all$$
equivalent:
Many other
$language$languages$
permit some form of integer-to-pointer type conversion.
Some pointer representations
$contained$contain$
status information, such as supervisor bits, as well as storage location
information.
Some pointer representations contain status information, such as
supervisor bits, as well
$$as$
storage location information.
In most cases a selection of bits from the pointer value
$are$is$
returned as the result.
Implementation vendors invariably do their best to ensure
$than$that$
such a mapping is supported by their implementations.
An implementation is not required
$$to$
provide their definitions in the header.
In source code that converts values having pointer types,
alignment-related issues are likely to be
$encounter$encountered$
quickly during program testing.
This problem is often encountered when porting a program from an
Intel x86-based host, few alignment restrictions, to a RISC
$base$based$
host, which usually has different alignment requirements for the
different integer types.
On such processors, it
$$is$
usually only the result of arithmetic operations that need to be
checked for being in canonical form.
(which
$violate$violates$
the guideline recommendation dealing with use of representation
information)
Some of the
$issue$issues$
involved in representing the null point constant in a consistent
manner are discussed elsewhere.
(an indirect call via an array index being deemed more efficient, in
time and/or space,
$that$than$
a switch statement)
The other cases that match against non-white-space
character that cannot be one of the above involve
characters that
$$are$
outside of the basic source character set.
Most developers are not aware
$of$$
that preprocessing-tokens exist.
Identifiers (whose spelling is under developer-control) and space
characters
$making$make$
up a large percentage of the characters on a line.
They
$$are$
also known as thelaws of perceptual organization.
$This$$
neurons within this area respond selectively to the orientation of
edges, the direction of stimulus movement, color along several
directions, and other visual stimuli.
It is common practice to
$preceded$precede$
the first non-white-space character on a sequence of lines to start
at the same horizontal position.
Their performance on a layout they have little
$inexperience$experience$
reading.
This characteristic affects performance when searching
$of$for$
an item when it occurs among visually similar items.
Treisman and Souther investigated this issue by having subjects
search for circles that differed in the presence
$of$or$
absence of a gap.
A study by Treisman and Souther found that visual
searches were
$performance$performed$
in parallel when the target included a unique feature.
As discussed in previous subsections, C source code is made up of
$$a$
fixed number of different characters.
This restricts the opportunities for organizing source to take
advantage of the search asymmetry of preattentive processing
$are limited$$
.
Those at the top include an
$items$item$
that has a distinguishing feature.
Saccade length is influenced by the
$lengths$length$
of both the fixated word and the word to the right of fixation.
The eyes' handling of visual data and the accuracy of
$its$their$
movement control are physical characteristics.
The characteristics of these words will be added
$that$to$
developers' existing word knowledge.
EMMA is based on many of the
$idea$ideas$
in the E-Z model and uses ACT-R to model cognitive processes.
(where it is likely to be the first non-space
$characters$character$
on a line)
Algorithms for automating the process
$$of$
separating words in unspaced text is an active research topic.
(they all had an undergraduate degree and were
$current$currently$
studying at the University of Pittsburgh)
A number of source code editors highlight (often by using different
colors) certain
$of$$
character sequences, for instance keywords.
(they are not formally defined
$them$$
using this term, but they appear in a clause with the title
]Reserved identifiers
[)
They are not part of the languages syntax, but they have a predefined
$a$$
special meaning.
Separating preprocessing tokens using white space
$$is$
more than a curiosity or technical necessity (in a few cases).
A rule similar to this is specified by most
$languages$language$
definitions.
Many commercial translators use hand-written lexers, where error
$recover$recovery$
can be handled more flexibly.
Developers
$to$do$
not always read the visible source in a top/down left-to-right order.
Having a sequence of characters that, but for this C rule, could be
lexed in a number of different ways
$$is$
likely to require additional cognitive effort.
Java was the first well-known
$languages$language$
to support universal-character-name characters in identifiers.
It also provides some recommendations that aim to
$prevents$prvent$
mistakes from being made in their usage.
The information provided by identifier names can operate at all
levels of source code construct, from providing helpful clues
$on$$
about the information represented in objects at the level of C
expressions to a means of encapsulating and giving context to a
series of statements and declaration in a function definition.
The result of this extensive experience is that individuals become
tuned to the commonly occurring sound and character patterns they
$encountered$encounter$
.
These
$are$$
recommendations are essentially filters of spellings that have
already been chosen.
For instance, what is the name of the object
$use$used$
to hold the current line count.
Different usability factors are likely to place different demands on
the choice of identifier spelling, requiring trade-offs
$need$$
to be made.
The availability of cheaper labour outside of the industrialized
nations is
$slowing$slowly$
shifting developers native language away from those nations languages
to Mandarin Chinese, Hindi/Urdu, and Russian.
The solution adopted here is to attempt to be natural-language
independent, while recognizing
$them$that$
most of the studies whose results are quoted used native English
speakers.
These
$trade-off$trade-offs$
also occur in their interaction with identifiers.
A nonword
$to$is$
sometimes read as a word whose spelling it closely resembles.
Whether particular identifier spellings are encountered by individual
developers
$sufficient$sufficient$
often, in C source code, for them to show a learning effect is not
known.
The process of creating a list of
$candidates$candidates$
is discussed in the first subsection that follows.
This point of first usage is the only time
$where$when$
any attempt at resource minimization is likely to occur.
(because additional uses may cause the relative importance
$of$$
given to the associated semantic attributes to change)
These suggestions are underpinned by the characteristics of both the
written and spoken forms of English and the characteristics of the
device
$use$used$
to process character sequences (the human brain).
Developers who primarily work within a particular host
$environments$environment$
(e.g., Linux or Microsoft Windows).
Automatic enforcement is assumed to
$$be$
the most likely method of checking adherence to these recommendations.
Whether this automated process occurs at the time
$of$$
an identifier is declared, or sometime later is a practical
cost/benefit issue that is left to the developer to calculate.
The similarity between two identifiers is measured using the typed
letters they
$contains$contain$
, their visual appearance, spoken form, and semantic form.
An algorithm for calculating the cognitive resources needed to
process an identifier spelling is
$$not$
yet available.
The primary human memory factors relevant to the filtering of
identifier spellings are the limited capacity of short-term memory
and
$it$its$
sound-based operating characteristics.
The letter sequences may be shorter,
$possible$possibly$
a single letter.
These are generally divided into vowels (open sounds, where there are
no obstructions to the flow
$the$of$
air from the mouth.
A category of letter sequences that often
$do$does$
not have the characteristics of words are peoples names, particularly
surnames.
Like relational interpretations, these have been found to
$be$$
occur between 30-70%.
Most Asian and Slavic
$language$languages$
, as well as many African languages have no articles, they use
article-like morphemes, or word order to specify the same information.
Help to indicate
$$that$
a word is not plural.
The cost of rehearsing information about locally declared identifiers
to improve recall performance is unlikely to
$$be$
recouped.
The performance of human memory can
$be$$
depend on whether information has to be recalled or whether presented
information has to be recognized.
For instance, in the
$cast$case$
of ]philatelist
many subjects recalled either
phil or ist.
For instance, the cue Something that can hold small
objects
is appropriate to paperclips (small objects) and
envelopes (being used to hold something), but not directly to
$and$an$
envelope being licked.
(where the glue cue would have a greater
$contextually$contextual$
match)
The visual similarity of words can affect
$performance$$
serial recall performance.
In
$a$$
many contexts a sequence of identifiers occur in the visible source,
and a reader processes them as a sequence.
To what extent can parallels be drawn between different kinds of
source code identifiers and different kinds of natural
$languages$language$
names?
For instance, agglutinative languages build words by adding affixes
to
$$the$
root word.
If people make
$spellings$spelling$
mistakes for words whose correct spelling they have seen countless
times, it is certain that developers will make mistakes.
The results show that for short documents subjects were able to
recall, with
$reasonably$reasonable$
accuracy, the approximate position on a page where information
occurred.
Some studies have attempted to measure confusability, while others
have
$attempt$attempted$
to measure similarity.
An example of internal word structure (affixes), and
$common a$a common$
convention for joining words together (peoples names), along with
tools for handling such constructs.
Some algorithms are rule-based, while
$other$others$
are dictionary-based.
Townsend used English subjects to produce
$a$$
confusion matrices for uppercase letters.
This pattern of response is
$consistence$consistent$
with subjects performing a visual match.
Source code identifiers may also
$$have$
another shape defining character.
The studies
$discussion$discussed$
in this subsection used either native British or American speakers of
English.
Two
$well-know$well-known$
kinds of mistake are:
They
$$found$
that in 99% of cases the target and erroneous word were in the same
grammatical category.
It is difficult to see how even detailed code reviews can reliably be
expected to highlight
$cultural$culturally$
specific assumptions, in identifier naming, made by project team
members.
Natural
$languages$language$
issues such as word order, the use of suffixes and prefixes, and ways
of expressing relationships, are discussed elsewhere.
Identifiers in local scope can be used and then forgotten about.
Individually these identifiers may only
$$be$
een by a small number of developers, compared to those at global
scope.
Studies have found that individuals and groups of people often
$minimization$minimize$
their use of resources implicitly, without conscious effort.
However, while it is possible to deduce an inverse power law
relationship between frequency and rank (Zipf's law) from the
principle of least effort, it cannot be assumed that any distribution
following this law is driven
$$by$
this principle.
In what order
$to$do$
people process an individual word?
It was proposed that the difference in performance was caused by the
position of vowels in words being more
$predictability$predictable$
than consonants, in English.
This is because each character represents an individual sound that is
not significantly affected by
$adjacent the$the adjacent$
characters.
Subsequent studies have
$show$shown$
that age of acquisition is the primary source of performance difference.
It was pointed
$$out$
that words learned early in life tend to be less abstract than those
learned later.
The process of extracting relations between words starts with a
matrix, where each row
$standards$stands$
for a unique word and each column stands for a context (which could
be a sentence, paragraph, etc.).
The process of extracting relations between words starts with a
matrix, where each row stands for a unique word and each column
$standards$stands$
for a context (which could be a sentence, paragraph, etc.).
Various mathematical operations are performed on the matrix to yield
results that have been found to
$be$$
effectively model human conceptual knowledge in a growing number of
domains.
(a total
$$of$
64 million words)
One point to note is that there was only one word corresponding
$the$to$
each letter sequence used in the study.
The most common algorithm
$use$used$
for shorter words was vowel deletion, while longer words tended to be
truncated.
The percentage of the original word's letters used in the
abbreviation
$decrease$decreased$
with word length.
(but editors rarely
$expands$expand$
them)
Few languages place limits on the maximum length of an identifier
that can
$be$$
appear in a source file.
Because a translator only ever needs to compare the spelling of one
identifier for equality with another identifier, which involves a
$simply$simple$
character by character comparison.
(because of greater practice with those
$character$characters$
)
Internal identifiers only need to be processed by the translator and
the standard is in a strong position to
$specifier$specify$
the behavior.
In most cases implementations support a sufficiently large number of
significant characters in an external name that a change of
identifier linkage makes no difference to
$the$$
its significant characters.
The contribution made
$$by$
characters occurring in different parts of an identifier will depend
on the pattern of eye movements employed by readers.
In many cases different identifiers
$denote also$also denote$
different entities.
It also enables a translator
$can$to$
have an identifier name and type predefined internally.
Java calls
$such$$
this lexical construct a UnicodeInputCharacter.
It is possible for every character in the source to
$be$$
appear in this form.
For instance, there are 60 seconds in a
$minutes$minute$
.
The single letter h probably gives no more information
$that$than$
the value.
(there is a potential
$advantages$advantage$
to be had from using octal constants)
Does
$should$$
this usage fall within the guideline recommendation dealing with use
of extensions.
For an implementation to support an integer constant which is not
representable by any standard integer type, requires that
$is$it$
support an extended integer type.
This term does not appear in the C++ Standard and it
$$is$
only used in this context in one paragraph.
Floating constants shall not
$containing$contain$
trailing zeros in their fractional part unless these zeros accurately
represent the known value of the quantity being represented.
For instance, implementations that interpret source code that has
been translated into the instructions of some
$an$$
abstract machine.
A source file may contain
$such$$
a constant that is not exactly representable.
For instance, a file containing a comma
$separate$separated$
list of values.
Octal and hexadecimal escape
$sequence$sequences$
provide a mechanism for developers to specify the numeric value of
individual execution time characters within an integer character
constant.
Although it is a little misleading in that it can be read to suggest
that both octal and hexadecimal escape sequences may consist
$or$of$
an arbitrary long sequence of characters.
The
$character$characters$
are nongraphical in the sense that they do not represent a glyph
corresponding to a printable character.
It is possible that an occurrence of such a character sequence will
cause a violation of syntax
$will$to$
occur.
Customer demand will ensure that
$translator$translators$
continue to have an option to support existing practice.
(Although some of their properties are known, their range is
specified and
$of$$
the digit characters have a contiguous encoding.)
Character constants are usually thought of in symbolic rather than
$a$$
numeric terms.
While there may not
$$be$
a worthwhile benefit in having a guideline recommending that names be
used to denote all string literals in visible source code.
Whichever method is used to indicate the operation, it usually
$take$takes$
place during program execution.
One
$different$difference$
between the " delimiter and the
< and > delimiters is that in
the former case developers are likely to have some control over the
characters that occur in the q-char-sequence.
A pp-number that occurs within a #if preprocessor directive is likely
to
$be$$
have a different type than the one it would be given as part of
translation phase 7.
(developers will be familiar with programs whose documentation has
been lost, or
$is$$
requires significant effort to obtain)
Having documentation available in the source file reduces information
access cost potentially leading to increased
$in$$
accuracy of the information used.
Duplicating information creates the problem of keeping both
up-to-date, and if they are differences between
$then$them$
, knowing which is correct.
(The update cost
$$is$
not likely to be recouped; deleting comments removes the potential
liability caused by them being incorrect.)
This
$directives$directive$
might control, for instance, the generation of listing files, the
alignment of storage, and the use of extensions.
The complexities seen in industrial strength translators are caused
by the desire to generate machine code that
$is$$
minimizes some attribute.
Performance is often an issue in programs that operate
$of$on$
floating-point data.
An example of this
$characteristics$characteristic$
is provided by so called garden path sentences.
This visible form of an expression, the number of characters it
occupies on a line and
$possible$possibly$
other lines, representing another form of information storage.
The approach taken in these coding guideline subsections is to
recommend, where possible, a usage that attempts
$$to$
nullify the effects of incorrect developer knowledge.
However, the author of the source does have some control over
$$how$
the individual operations are broken down and how the written form is
presented visually.
The last two suggestions will only apply if
$are there$there are$
semantically meaningful subexpressions into which the full expression
can be split.
Are there any benefits in splitting an expression at any particular
$points$point$
, or in visually organizing the lines in any particular manner?
The edges of the code (the first non-white-space characters at the
start and end of lines) are often used as reference points
$used$$
when scanning the source.
This developer
$though$thought$
process leads on to the idea that performing as many operations as
much as possible within a single expression evaluation results in
translators generating more efficient machine code.
Citron
$$studied$
how processors might detect previously executed instruction sequences
and reuse the saved results (assuming the input values were the same).
(it tends to be
$more$$
greater in markets where processor cost has been traded-off against
performance)
Treating the same object as having different representations, in
different parts of the visible source, requires readers to use two
different mental
$$models$
of the object.
It means that the final result of an expression is different than it
would have been had several independent instructions
$had$$
been used.
While an infinite number of combined processor
$possible$$
instructions are possible, only a few combinations occur frequently
in commercial applications.
Requiring developers to read
$listing$listings$
of generated machine code probably does not count as clearly
documented.
But, for the use of expression rewriting by an optimizer, the
generated machine code will also
$$be$
identical.
(because such a requirement invariably exists in other computer
$language$languages$
)
The use of pointers rather
$$than$
arrays makes some optimizations significantly more difficult to
implement.
Knowing that there is no dependency between two accesses allows an
optimizer to order them as
$is$it$
sees fit.
It is sometimes
$claim$claimed$
that having arrays zero based results in more efficient machine code
being generated.
It is not possible to assign
$tall$all$
of b's elements in one assignment statement.
It is possible that developers will
$$be$
more practiced in the use of this form.
Those languages that support some
$a$$
form of function declaration that includes parameter information.
An analysis by Miller and Rozas showed that allocating storage on a
stack to hold information associated with function calls was more
time efficient
$that$than$
allocating it on the heap.
Genetic algorithms have been proposed
$$as$
a general solution to the problem.
When the postfix expression is not
$$an$
identifier denoting the name of a function, but an object having a
pointer to function type, it can be difficult to deduce which
function. is being is called.
Some languages use the convention that a function call always returns
a value, while procedure (or subroutine) calls never
$a return$return a$
value.
Are the
$alternatives$alternative$
more costly than the original problem, if there is one?
For other kinds of arguments, more information on the cost/benefit of
explicit casts/suffixes for arguments is needed before it is possible
$$to$
estimate whether any guideline recommendation is worthwhile.
More information on the cost/benefit of explicit casts, for
arguments, is needed before it is possible
$$to$
evaluate whether any guideline recommendation is worthwhile.
There are
$constraint$constraints$
that ensure that this conversion is possible.
There is no concept of
$start$starting$
and stopping, as such, argument conversion in C++.
That is,
$there are$$
no implicit conversions are applied to them at the point of call.
In C++ it is possible
$to$for$
definitions written by a developer to cause implicit conversions.
This unspecified behavior is a special case of an
$issues$issue$
covered by a guideline recommendation.
This notation is common to most languages that support some
$from$form$
of structure or union type.
Processors invariably support a register+offset
addressing mode, where the base address of an object
$is$has already$
been loaded into register.
The member selections are intermediate steps toward the access
$$of$
a particular member.
But if these types do not appear together within the same union type,
a translator is free to assume that pointers to objects having these
two structure types are never
$be$$
aliases of each other.
All implementations known to your author assign the same offset to
$a$$
members of different structure types.
These involve pointers and pointers to different structure types
$which$$
are sometimes cast to each others types.
In the following example the body of the function f
is encountered before the translator finds out that objects it
contains
$access have$have access$
types that are part of a common initial sequence.
The total cognitive effort needed to comprehend the first equivalent
form may be
$the$$
more than the postfix form.
The total cognitive effort needed to comprehend the second equivalent
form may be
$$the$
same as the original and the peak effort may be less.
Are more faults likely to be introduced through
$the$$
miscomprehension.
It also requires that two values be temporarily
$be$$
associated with the same object.
There is also the possibility of
$be$$
interference between the two, closely semantically associated, values.
(causing one or both of them
$$to$
be incorrectly recalled)
The postfix ++ operator is treated the same as any other operator
$than$that$
modifies an object.
It is also possible that the operand may be modified more than once
between two
$sequences$sequence$
points, causing undefined behavior.
The type of the compound literal is deduced
$form$from$
the type name.
(the storage for one only need be allocated
$while$$
during the lifetime of its enclosing block)
This is needed because C++ does not
$defined$define$
its boolean type in the same way as C.
Taking the address of an object could effectively
$prevents$prevent$
a translator from keeping its value in a register.
Is it possible to specify a set of objects whose addresses should not
be taken and what are the costs of having
$to$no$
alternatives for these cases?
Is it possible to specify a set of objects whose addresses should not
be
$token$taken$
and what are the costs of having no alternatives for these cases?
It may simplify storage management if this is a pointer to an object
$a$at$
file scope.
This difference is only significant for reference types, which are
not
$support$supported$
by C.
Other languages obtain the size implicitly in those contexts where
$$it$
is needed.
(which can
$$be$
used to implement the cast operation)
An alternative implementation technique, in those cases where no
conversion instruction is available, is for the implementation to
$have$$
specify all floating-point types as having the same representation.
A study by LeFevre gave subjects single-digit multiplication problems
to solve and
$them$then$
asked them what procedure they had used to solve the problems.
Measurements by Citron found that in a high percentage
$$of$
cases, the operands of multiplication operations repeat themselves.
More strongly typed languages require that pointer declarations fully
specify the type of object
$pointer$pointed$
at.
Here it is used
$$in the$
same sense as that used for arithmetic values.
Developers rarely intend to reference storage via
$a$$
such a pointer value.
The ILE C documentation is silent on the
$issues$issue$
of this result not being representable.
If the next
$operations$operation$
is an assignment to an object having the same type as the operand
type an optimizer might choose to make use of one of these narrower
width instructions.
Others require that the amount to shift by
$is$be$
loaded into a register.
The sign bit is ignored and it
$remained$remains$
unchanged by the shift instruction.
For instance, a study by Moyer gave four made-up names to four
circles of different
$diameter$diameters$
.
Neither is anything said about the behavior of relational operators
when their operands
$pointer$point$
to different objects.
Relational comparisons between indexes into two different array
objects rarely have any meaning and the standard does not define such
support
$one$$
for pointers.
The case where only one operand is a pointer is when the other
operand is the integer constant 0 being interpreted
$$as a$
null pointer constant.
These conversions
$occurs$occur$
when two operands have pointer type.
Other coding guideline documents sometimes specify that these two
operators should not be confused, or list
$then$them$
in review guidelines.
The following list of constraints ensures that the value of both
operands can be operated on in the same
$$way$
by subsequent operators.
The following list of constraints ensures that the value of both
operands can be operated on in the same way by
$subsequence$subsequent$
operators.
Unlike the controlling expression in a selection statement, this
operand is not a full expression, so this specification of a sequence
point is necessary to
$full$fully$
define the evaluation order.
If the operands have void type, the only affect on
$to$$
the output of the program is through the side effects of their
evaluation.
The evaluation of the operands has the same behavior as most
$the$$
other binary operators in C.
The guideline recommendation
$$for$
binary operators with an operand having an enumeration type is
applicable here.
A surprising number of assignment operations store a value that is
equal to the value already
$in$$
held in memory.
Compound assignment requires less effort to comprehend
$that$than$
its equivalent two operator form.
It is usually used to simplify the analysis that needs to be
performed by the generator in deducing
$out$$
what it has to do.
(which
$that$$
can occur in any context an expression can occur in)
For a discussion of how people
$story$store$
arithmetic facts in memory see Whalen.
The C abstract machine does not
$existing$exist$
during translation.
Many
$language$languages$
only permit pointers to point at dynamically created objects.
However, this restriction
$$is$
cumbersome and was removed in Ada 95.
As the following example shows, the surrounding declarations play an
important role in determining how individual identifiers
$standard$stand$
out, visually.
(on the basis
$$that$
source code readers would not have to scan a complete declaration
looking for the information they wanted, like looking a word up in a
dictionary it would be in an easy to deduce position)
The C++ wording covers all of the
$case$cases$
covered by the C specification above.
Researchers of human reasoning are usually attempting to understand
the mechanisms underlying
$of$$
human cognition.
More experiments need to be performed before it is possible to
reliably draw
$firm any$any firm$
conclusions about the consequences of using different kinds of
identifier in assignment statements and on developer performance
during source code comprehension.
Frequency
$$of$
identifiers having a particular spelling.
Analysis of the properties of English words suggest that they are
optimized for recognition, based on their spoken form, using
$on$$
their initial phonemes.
It has now
$$been$
officially superseded by C99.
Vendors interested in low power consumption try to design
$$to$
minimize the number of gate transitions made during the operation of
a processor.
The presence
$$of$
a pipeline can affect program execution, depending on processor
behavior when an exception is raised during instruction execution.
For instance,
$the$$
defining an object at file scope is often considered to be a more
important decision than defining one in block scope.
This means that either an available format is used, or additional
instruction
$be$is$
executed to convert the result value (slowing the performance of the
application).
As such
$.$,$
this evaluation format contains the fewest surprises for a developer
expecting the generated machine code to mimic the type of operations
in the source code.
For instance
$.$,$
using an assignment operator.
For the result of the sizeof operator to be an integer constant
$.$,$
its' operand cannot have a VLA type.
A similar statement for the alphabetic characters cannot be
$make$made$
because it would not be true for EBCDIC.
The main
$holes$hole$
in my cv. is a complete lack of experience in generating code for
DSPs and vector processors.
Cache behavior when a processor is executing more than
one program at the same time can be
$quiet$quite$
complex.
(perhaps some Cobol and Fortran programmers may soon
$achieved$achieve$
this).
Writing a compiler for a language is the only way to get to know it
in depth and while I have
$many used$used many$
other languages I can only claim to have expertise in a few of them.
The two perennial needs of performance and compatibility with
existing practice often result in vendors making design choices that
significantly affect how developers
$interacted$interact$
with their products.
This is where we point out what the difference,
$if$is$
any, and what the developer might do, if anything, about it.
However, there are
$a$$
some optimizations that involve making a trade-off between
performance and size.
For this reason optimization techniques often take many years to find
their way from published papers to commercial products,
$it$if$
at all.
But the meaning
$is$$
appears to be the same.
Some studies have looked at how developers differ
$i$$
(which need not be the same as measuring expertise), including their:
Humans are not ideal machines, an assertion
$$that$
may sound obvious.
Although there is a plentiful supply
$is$of$
C source code publicly available this source is nonrepresentative in
a number of ways, including:
Programs whose source code was used as the input to tools whose
measurements
$was$were$
used to generate this books usage figures and tables.
This is usually because of the use
$$of$
dynamic data structures, which means that their only fixed limit is
the amount of memory available during translation.
Although a sequence of source code may be an erroneous program
construct, a translator is only required to issue a diagnostic
message for a syntax violation
$of$or$
a constraint violation.
Some translators
$prove$provide$
options that allow the developer to select the extent to which a
translator will attempt to diagnose these constructs.
There is something of a circularity in the C Standard's definition
$$of$
byte and character.
There are a large number of character sets, one for almost
$ever$every$
human language in the world.
However, neither
$organizations$organization$
checked the accuracy of the documented behavior.
It is recommended that small test programs be written to verify that
an
$implementations$implementation's$
behavior is as documented.
The effect is to prevent line
$from splicing$splicing from$
occurring and invariably causes a translator diagnostic to be issued.
Many linkers do not include function definitions that are never
$references$referenced$
in the program image.
The extent to which it is cost effective to use the information
provided by the status flags is outside the scope of these coding
$guideline$guidelines$
.
Most character encodings do not contain any combining characters, and
those
$they$that$
do contain them rarely specify whether they should occur before or
after the modified base character.
$Suffixed$Suffixes$
are generally used, rather than hexadecimal notation, to specify
unsigned types.
Most compiler
$book$books$
limit there discussion to LR and LL related methods.
This encoding can vary from the relatively simply, or
$quiet$quite$
complex.
(such as limits
$$on$
how objects referenced by restricted pointers are accessed)
The technical difficulties involved in proving that a developer's use
of restrict has defined behavior
$is$are$
discussed elsewhere.
The situation is more complicated when the translated output comes
from both a C
$$and$
a C++ translator.
A few languages (e.g., Algol 68)
$has$have$
a concept similar to that of abstract declarator.
it is also necessary to set or reset a flag based on the current
syntactic context, because an identifier should only be looked up, to
find out if it is currently defined as a
typedef-name,
$is$in$
a subset of the contexts in which an identifier can occur.
Until more is known about the frequency with which individual
initializers are read for comprehension, as opposed to being given a
$cursor$cursory$
glance it is not possible to reliably provide cost effective
recommendations about how to organize their layout.
Just like simple assignment, it is possible
$$to$
initialize a structure or union object with the value of another
object having the same type.
(one of them
$possible$possibly$
being the null pointer constant)
For this reason this guideline subsection is silent on the issue of
how loops might
$termination$terminate$
.
Most other languages do not support having anything
$$other than$
the loop control variable tested against a value that is known at
translation time.
(the wording in a subsequent example suggests that being visible
rather than in scope
$is$$
more accurately reflects the intent)
(
$he$the$
operators have to be adjacent to the preprocessing tokens that they
operate on)
Without this information it is not possible
$$to$
estimate the cost/benefit of any guideline recommendations and none
are made here.
The expansion of a macro
$$may$
not result in a sequence of tokens that evaluate its arguments more
than once.
(i.e., as soon as a 1 is shifted through it, its value
$says$stays$
set at 1)