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[ Mar 24  2004] Open source development using C99 Is your C code up to standard? by Peter Seebach ([email protected]) What is C99? Who needs it? Is it available yet? Peter Seebach discusses the 1999 revision of the ISO C standard, with a focus on the availability of new features on Linux and BSD systems.

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There are two parts of the C programming language. These are, confusingly, called the "language" and the "library." Historically, there was a bundle of commonly used utility code that everyone tended to reuse; this was eventually standardized into what's called the Standard C Library. The distinction was pretty easy to understand at first: If the compiler did it, it was the language; if it was in the add-on code, it was the library.

With time, however, the distinction has been blurred. For instance, some compilers will generate calls to an external library for 64-bit arithmetic, and some library functions might be handled magically by the compiler. For the purposes of this article, the division follows the terminology of the standard: features from the "Library" section of the standard are library features and are discussed in the next section of the article. This section looks at everything else.

The C99 language introduces a number of new features that are of potential interest to software developers. Many of these features are similar to features of the GNU C set of extensions to C; unfortunately, in some cases, they are not quite compatible.

A few features popularized by C++ have made it in. In particular, // comments and mixed declarations and code have become standard features of C99. These have been in GNU C forever and should work on every platform. In general, though, C and C++ remain separate languages; indeed, C99 is a little less compatible with C++ than C89 was. As always, trying to write hybrid code is a bad idea. Good C code will be bad C++ code.

C99 added some support for Unicode characters, both within string literals and in identifiers. In practice, the system support for this probably isn't where it needs to be for most users; don't expect source that uses this to be accessible to other people just yet. In general, the wide character and unicode support is mostly there in the compiler, but the text processing tools aren't quite up to par yet.

The new variable-length array (VLA) feature is partially available. Simple VLAs will work. However, this is a pure coincidence; in fact, GNU C has its own variable-length array support. As a result, while simple code using variable-length arrays will work, a lot of code will run into the differences between the older GNU C support for VLAs and the C99 definition. Declare arrays whose length is a local variable, but don't try to go much further.

Compound literals and designated initializers are a wonderful code maintainability feature. Compare these two code fragments:

Listing 1. Delaying for n microseconds in C89
 

/* C89 */ { struct timeval tv = { 0, n }; select(0, 0, 0, 0, &tv); }

 

Listing 2. Delaying for n microseconds in C99
 

// C99 select(0, 0, 0, 0, & (struct timeval) { .tv_usec = n });

The syntax for a compound literal allows a brace-enclosed series of values to be used to initialize an automatic object of the appropriate type. The object is reinitialized each time its declaration is reached, so it's safe with functions (such as some versions of select) that may modify the corresponding object. The designated initializer syntax allows you to initialize members by name, without regard to the order in which they appear in an object. This is especially useful for large and complicated objects with only a few members initialized. As with a normal aggregate initializer, missing values are treated as though they'd been given 0 as an initializer. Other initialization rules have changed a bit. For instance, you're now allowed to have a trailing comma after the last member of an enum declaration, to make it just a bit easier to write code generators.

For years, people have been debating extensions to the C type system, such as long long. C99 introduces a handful of new integer types. The most widely used is long long. Another type introduced by the standards process is intmax_t. Both of these types are available in gcc. However, the integer promotion rules are not always correct for types larger than long. It's probably best to use explicit casts.

There are also a lot of types allowing more specific descriptions of desired qualities. For instance, there are types with names like int_least8_t, which has at least 8 bits, and int32_t, which has exactly 32 bits. The standard guarantees access to types of at least 8, 16, 32, and 64 bits. There is no promise that any exact-width types will be provided. Don't use such types unless you are really, totally sure that you can't accept a larger type. Another optional type is the new intptr_t type, which is an integer large enough to hold a pointer. Not all systems provide such a type (although all current Linux and BSD implementations do).

The C preprocessor has a number of new features. It allows empty arguments, and it supports macros with varying numbers of arguments. There is a _Pragma operator for macro-generating pragmas, and there's a __func__ macro, which always contains the name of the current function. These features are available in current versions of gcc.

C99 added the inline keyword to suggest function inlining. GNU C also supports this keyword, but with slightly different semantics. If you're using gcc, you should always use the static keyword on inline functions if you want the same behavior as C99 would give for the code. This may be addressed in future revisions; in the meantime, you can use inline as a compiler hint, but don't depend on the exact semantics.

C99 introduced a qualifier, restrict, which can give a compiler optimization hints about pointers. Because there is no requirement that a compiler do anything with this, it's done in that gcc accepts it. The degree of optimization done varies. It's safe to use, but don't count on it making a huge difference yet. On a related note, the new type-aliasing rules are fully supported in gcc. This mostly means that you must be more careful about type punning, which is almost always going to invoke undefined behavior, unless the type you're using to access data of the wrong sort is unsigned char.

Array declarators as function arguments now have a meaningful difference from pointer declarators: you can put in type qualifiers. Of particular interest is the very odd optimizer hint of giving an array declarator the static type modifier. Given this declaration: int foo(int a[static 10]);

It is undefined behavior to call foo() with a pointer that doesn't point to at least 10 objects of type int. This is an optimizer hint. All you're doing is promising the compiler that the argument passed to the function will be at least that large; some machines might use this for loop unrolling. As old hands will be well aware, it's not a new C standard without an entirely new meaning for the static keyword.

One last feature to mention is flexible array members. There is a common problem of wanting to declare a structure that is essentially a header followed by some data bytes. Unfortunately, C89 provided no good way to do this without giving the structure a pointer to a separately allocated region. Two common solutions included declaring a member with exactly one byte of storage, then allocating extra and overrunning the bounds of the array, and declaring a member with more storage than you could possibly need, underallocating, and being careful to use only the storage available. Both of these were problematic for some compilers, so C99 introduced a new syntax for this:

Listing 3. A structure with a flexible array
 

struct header { size_t len; unsigned char data[]; };

This structure has the useful property that if you allocate space for (sizeof(struct header) + 10) bytes, you can treat data as being an array of 10 bytes. This new syntax is supported in gcc.

Library features
That's fine for the compiler. What about the standard library? A lot of the library features added in C99 were based on existing practice, especially practices found in the BSD and Linux communities. So, many of these features are preexisting ones already found in the Linux and BSD standard libraries. Many of these features are simple utility functions; almost all of them could in principle be done in portable code, but many of them would be exceedingly difficult.

Some of the most convenient features added in C99 are in the printf family of functions. First, the v*scanf functions have become standardized; for every member of the scanf family, there is a corresponding v*scanf function that takes a va_list parameter instead of a variable argument list. These functions serve the same role as the v*printf functions, allowing user-defined functions that take variable argument lists and end up calling a function from the printf or scanf family to do the hard work.

Secondly, the 4.4BSD snprintf function family has been imported. The snprintf function allows you to print safely into a buffer of fixed size. When told to print no more than n bytes, snprintf guarantees that it creates a string of length no more than n-1, with a null terminator at the end of the string. However, its return code is the number of characters it would have written if n had been large enough. Thus, you can reliably find out how much buffer space you would need to format something completely. This function is available everywhere, and you should use it just about all the time; a lot of security holes have been based on buffer overruns in sprintf, and this can protect against them.

A number of new math features, including complex math features and special functions designed to help optimizing compilers for specific floating point chips are in the new standard, but not reliably implemented everywhere. If you need these functions, it is best to check on the exact platform you're targeting. The floating point environment functions are not always supported, and some platforms will not have support for IEEE arithmetic. Don't count on these new features yet.

The strftime() function has been extended in C99 to provide a few more commonly desired formatting characters. These new characters appear to be available on recent Linux and BSD systems; they aren't always widely available on somewhat older systems, though. Check the documentation before using new formats.

As noted, most of the internationalization code is not reliably implemented yet.

Other new library features are typically not universally available; the math functions are likely to be available in supercomputer compilers, and the internationalization functions are likely to be available in compilers developed outside the United States. Compiler vendors implement the features they have a call for.

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Resources

• The current status of C99 language work is on the GNU project's page. New versions of gcc will probably change some of these.
• WG14 is the ISO working group that produced C99.
• Wiley produces a hardcopy version of ISO C 1999, including the first Technical Corrigendum (ISBN 0-470-84573-2).
• The Rationale for the C99 standard is available online in PDF format.
• Kernighan & Ritchie's The C Programming Language was the first to describe C. The original ANSI standard was based on the first edition of the book, and in return the second edition of the book described the ANSI standard. It has editions in everything from Finnish to Chinese to Hebrew to Braille. You might also enjoy Dennis Ritchie's history of C.
• Many members of IBM's C and C++ family of products are C99-compliant including VisualAge C++ for AIX Version 6.0, an advanced C/C++ compiler available for AIX and Linux. More details can be found in this announcement from 2002 (in PDF format). Even more details can be found in C for AIX, Version 6.0, C/C++ Language Reference (in PDF).
• Learn more about the standards involved with Unicode and internationalization in "Linux Unicode programming" (developerWorks, August 2001)
• The Dinkum C99 Library Reference Manual is an excellent resource.
• The article Are you Ready For C99? (Kuro5hin, 2001) gives a nice overview of C99.
• Comeau Computing has posted a Tech Talk About C99 with lots of sample code to illustrate new features, from _Bool to _func_ and much more.
• Thomas Wolf has a page of information regarding the ISO standard for the C language. Thomas' page includes a link to his summary of the most important changes in C99, which also chronicles new functions and features and how to use them.
• David R. Tribble's Incompatibilities Between ISO C and ISO C++ discusses those places where C99 and C++98 clash.
• Find more resources for Linux developers in the developerWorks Linux zone.

 kuro5hin.org/Are you Ready For C99

Status of C99 features in GCC - GNU Project - Free Software ...

Tech Talk about C++ and C Issues - Comeau C++ and C FAQ

Dinkum C99 Library Reference

C9X -- The New C Standard

C99.ORG

Open source development using C99

Recommended Links

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See also Selected Computing Sciences Technical Reports from Bell Labs

• A development of the C language by Dennis Ritchie

  1.4      Origins: the languages 

  BCPL was designed by Martin Richards in the mid-1960s while he was visiting MIT, and was used during the early 1970s for several interesting projects, among them the OS6 operating system at Oxford [Stoy 72], and parts of the seminal Alto work at Xerox PARC [Thacker 79]. We became familiar with it because the MIT CTSS system [Corbato 62] on which Richards worked was used for Multics development. The original BCPL compiler was transported both to Multics and to the GE-635 GECOS system by Rudd Canaday and others at Bell Labs [Canaday 69]; during the final throes of Multics's life at Bell Labs and immediately after, it was the language of choice among the group of people who would later become involved with Unix.

  BCPL, B, and C all fit firmly in the traditional procedural family typified by Fortran and Algol 60. They are particularly oriented towards system programming, are small and compactly described, and are amenable to translation by simple compilers. They are `close to the machine' in that the abstractions they introduce are readily grounded in the concrete data types and operations supplied by conventional computers, and they rely on library routines for input-output and other interactions with an operating system. With less success, they also use library procedures to specify interesting control constructs such as coroutines and procedure closures. At the same time, their abstractions lie at a sufficiently high level that, with care, portability between machines can be achieved.

  BCPL, B and C differ syntactically in many details, but broadly they are similar. Programs consist of a sequence of global declarations and function (procedure) declarations. Procedures can be nested in BCPL, but may not refer to non-static objects defined in containing procedures. B and C avoid this restriction by imposing a more severe one: no nested procedures at all. Each of the languages (except for earliest versions of B) recognizes separate compilation, and provides a means for including text from named files.

  Several syntactic and lexical mechanisms of BCPL are more elegant and regular than those of B and C. For example, BCPL's procedure and data declarations have a more uniform structure, and it supplies a more complete set of looping constructs. Although BCPL programs are notionally supplied from an undelimited stream of characters, clever rules allow most semicolons to be elided after statements that end on a line boundary. B and C omit this convenience, and end most statements with semicolons. In spite of the differences, most of the statements and operators of BCPL map directly into corresponding B and C.

  Some of the structural differences between BCPL and B stemmed from limitations on intermediate memory. For example, BCPL declarations may take the form

  let P1 be command

  and P2 be command

  and P3 be command

  where the program text represented by the commands contains whole procedures. The subdeclarations connected by and occur simultaneously, so the name P3 is known inside procedure P1. Similarly, BCPL can package a group of declarations and statements into an expression that yields a value, for example  

  E1 := valof $( declarations ; commands ; resultis E2 $) + 1

  The BCPL compiler readily handled such constructs by storing and analyzing a parsed representation of the entire program in memory before producing output. Storage limitations on the B compiler demanded a one-pass technique in which output was generated as soon as possible, and the syntactic redesign that made this possible was carried forward into C.

  Certain less pleasant aspects of BCPL owed to its own technological problems and were consciously avoided in the design of B. For example, BCPL uses a `global vector' mechanism for communicating between separately compiled programs. In this scheme, the programmer explicitly associates the name of each externally visible procedure and data object with a numeric offset in the global vector; the linkage is accomplished in the compiled code by using these numeric offsets. B evaded this inconvenience initially by insisting that the entire program be presented all at once to the compiler. Later implementations of B, and all those of C, use a conventional linker to resolve external names occurring in files compiled separately, instead of placing the burden of assigning offsets on the programmer.

  Other fiddles in the transition from BCPL to B were introduced as a matter of taste, and some remain controversial, for example the decision to use the single character = for assignment instead of :=. Similarly, B uses /**/ to enclose comments, where BCPL uses //, to ignore text up to the end of the line. The legacy of PL/I is evident here. (C++ has resurrected the BCPL comment convention.) Fortran influenced the syntax of declarations: B declarations begin with a specifier like auto or static, followed by a list of names, and C not only followed this style but ornamented it by placing its type keywords at the start of declarations. 

  Not every difference between the BCPL language documented in Richards's book [Richards 79] and B was deliberate; we started from an earlier version of BCPL [Richards 67]. For example, the endcase that escapes from a BCPL switchon statement was not present in the language when we learned it in the 1960s, and so the overloading of the break keyword to escape from the B and C switch statement owes to divergent evolution rather than conscious change. 

  In contrast to the pervasive syntax variation that occurred during the creation of B, the core semantic content of BCPL­its type structure and expression evaluation rules­remained intact. Both languages are typeless, or rather have a single data type, the `word,' or `cell,' a fixed-length bit pattern. Memory in these languages consists of a linear array of such cells, and the meaning of the contents of a cell depends on the operation applied. The + operator, for example, simply adds its operands using the machine's integer add instruction, and the other arithmetic operations are equally unconscious of the actual meaning of their operands. Because memory is a linear array, it is possible to interpret the value in a cell as an index in this array, and BCPL supplies an operator for this purpose. In the original language it was spelled rv, and later !, while B uses the unary *. Thus, if p is a cell containing the index of (or address of, or pointer to) another cell, *p refers to the contents of the pointed-to cell, either as a value in an expression or as the target of an assignment. 

  Because pointers in BCPL and B are merely integer indices in the memory array, arithmetic on them is meaningful: if p is the address of a cell, then p+1 is the address of the next cell. This convention is the basis for the semantics of arrays in both languages. When in BCPL one writes 

  let V = vec 10

  or in B,  

  auto V[10];

  the effect is the same: a cell named V is allocated, then another group of 10 contiguous cells is set aside, and the memory index of the first of these is placed into V. By a general rule, in B the expression 

  *(V+i)

  adds V and i, and refers to the i-th location after V. Both BCPL and B each add special notation to sweeten such array accesses; in B an equivalent expression is 

  V[i]

  and in BCPL

  V!i

  This approach to arrays was unusual even at the time; C would later assimilate it in an even less conventional way.

  None of BCPL, B, or C supports character data strongly in the language; each treats strings much like vectors of integers and supplements general rules by a few conventions. In both BCPL and B a string literal denotes the address of a static area initialized with the characters of the string, packed into cells. In BCPL, the first packed byte contains the number of characters in the string; in B, there is no count and strings are terminated by a special character, which B spelled `*e'. This change was made partially to avoid the limitation on the length of a string caused by holding the count in an 8- or 9-bit slot, and partly because maintaining the count seemed, in our experience, less convenient than using a terminator. 

  Individual characters in a BCPL string were usually manipulated by spreading the string out into another array, one character per cell, and then repacking it later; B provided corresponding routines, but people more often used other library functions that accessed or replaced individual characters in a string.

  1.5      More History 

  After the TMG version of B was working, Thompson rewrote B in itself (a bootstrapping step). During development, he continually struggled against memory limitations: each language addition inflated the compiler so it could barely fit, but each rewrite taking advantage of the feature reduced its size. For example, B introduced generalized assignment operators, using x=+y to add y to x. The notation came from Algol 68 [Wijngaarden 75] via McIlroy, who had incorporated it into his version of TMG. (In B and early C, the operator was spelled =+ instead of += ; this mistake, repaired in 1976, was induced by a seductively easy way of handling the first form in B's lexical analyzer.) 

  Thompson went a step further by inventing the ++ and -- operators, which increment or decrement; their prefix or postfix position determines whether the alteration occurs before or after noting the value of the operand. They were not in the earliest versions of B, but appeared along the way. People often guess that they were created to use the auto-increment and auto-decrement address modes provided by the DEC PDP-11 on which C and Unix first became popular. This is historically impossible, since there was no PDP-11 when B was developed. The PDP-7, however, did have a few `auto-increment' memory cells, with the property that an indirect memory reference through them incremented the cell. This feature probably suggested such operators to Thompson; the generalization to make them both prefix and postfix was his own. Indeed, the auto-increment cells were not used directly in implementation of the operators, and a stronger motivation for the innovation was probably his observation that the translation of ++x was smaller than that of x=x+1. 

  The B compiler on the PDP-7 did not generate machine instructions, but instead `threaded code' [Bell 72], an interpretive scheme in which the compiler's output consists of a sequence of addresses of code fragments that perform the elementary operations. The operations typically­in particular for B­act on a simple stack machine.

  On the PDP-7 Unix system, only a few things were written in B except B itself, because the machine was too small and too slow to do more than experiment; rewriting the operating system and the utilities wholly into B was too expensive a step to seem feasible. At some point Thompson relieved the address-space crunch by offering a `virtual B' compiler that allowed the interpreted program to occupy more than 8K bytes by paging the code and data within the interpreter, but it was too slow to be practical for the common utilities. Still, some utilities written in B appeared, including an early version of the variable-precision calculator dc familiar to Unix users [McIlroy 79]. The most ambitious enterprise I undertook was a genuine cross-compiler that translated B to GE-635 machine instructions, not threaded code. It was a small tour de force: a full B compiler, written in its own language and generating code for a 36-bit mainframe, that ran on an 18-bit machine with 4K words of user address space. This project was possible only because of the simplicity of the B language and its run-time system. 

  Although we entertained occasional thoughts about implementing one of the major languages of the time like Fortran, PL/I, or Algol 68, such a project seemed hopelessly large for our resources: much simpler and smaller tools were called for. All these languages influenced our work, but it was more fun to do things on our own.

  By 1970, the Unix project had shown enough promise that we were able to acquire the new DEC PDP-11. The processor was among the first of its line delivered by DEC, and three months passed before its disk arrived. Making B programs run on it using the threaded technique required only writing the code fragments for the operators, and a simple assembler which I coded in B; soon, dc became the first interesting program to be tested, before any operating system, on our PDP-11. Almost as rapidly, still waiting for the disk, Thompson recoded the Unix kernel and some basic commands in PDP-11 assembly language. Of the 24K bytes of memory on the machine, the earliest PDP-11 Unix system used 12K bytes for the operating system, a tiny space for user programs, and the remainder as a RAM disk. This version was only for testing, not for real work; the machine marked time by enumerating closed knight's tours on chess boards of various sizes. Once its disk appeared, we quickly migrated to it after transliterating assembly-language commands to the PDP-11 dialect, and porting those already in B. 

  By 1971, our miniature computer center was beginning to have users. We all wanted to create interesting software more easily. Using assembler was dreary enough that B, despite its performance problems, had been supplemented by a small library of useful service routines and was being used for more and more new programs. Among the more notable results of this period was Steve Johnson's first version of the yacc parser-generator [Johnson 79a]. 

• 'Programming in C A Tutorial' (1974)

• Short history of the language C.

• Brian W. Kernighan home page

• ***** Why Pascal is Not My Favorite Programming Language by B. W. Kernighan  -- Must read. A rebellious paper written at the time of when structured programming and verification religious movement was close to its top, and to criticize Pascal what rather dangerous undertaking. Kerningan has problems with finding a publisher.

• The C9X Charter as revised at the June 1995 meeting in Copenhagen

• Original Principles

  Before embarking on a revision of the C Standard, it is useful to reflect on the charter of the original drafting committee. According to the original Rationale Document in the section entitled ``Purpose:''

  The work of the Committee was in large part a balancing act. The Committee has tried to improve portability while retaining the definition of certain features of C as machine-dependent. It attempted to incorporate valuable new ideas without disrupting the basic structure and fabric of the language. It tried to develop a clear and consistent language without invalidating existing programs. All of the goals were important and each decision was weighed in the light of sometimes contradictory requirements in an attempt to reach a workable compromise.

  In specifying a standard language, the Committee used several guiding principles, the most important of which are:

  1. Existing code is important, existing implementations are not. A large body of C code exists of considerable commercial value. Every attempt has been made to ensure that the bulk of this code will be acceptable to any implementation conforming to the Standard. The Committee did not want to force most programmers to modify their C programs just to have them accepted by a conforming translator.

  On the other hand, no one implementation was held up as the exemplar by which to define C: It is assumed that all existing implementations must change somewhat to conform to the Standard.

  2. C code can be portable. Although the C language was originally born with the UNIX operating system on the DEC PDP-11, it has since been implemented on a wide variety of computers and operating systems. It has also seen considerable use in cross-compilation of code for embedded systems to be executed in a free-standing environment. The Committee has attempted to specify the language and the library to be as widely implementable as possible, while recognizing that a system must meet certain minimum criteria to be considered a viable host or target for the language.

  3. C code can be non-portable. Although it strove to give programmers the opportunity to write truly portable programs, the Committee did not want to force programmers into writing portably, to preclude the use of C as a ``high-level assembler;'' the ability to write machine-specific code is one of the strengths of C. It is this principle which largely motivates drawing the distinction between strictly conforming program and conforming program.

  4. Avoid ``quiet changes.'' Any change to widespread practice altering the meaning of existing code causes problems. Changes that cause code to be so ill-formed as to require diagnostic messages are at least easy to detect. As much as seemed possible, consistent with its other goals, the Committee has avoided changes that quietly alter one valid program to another with different semantics, that cause a working program to work differently without notice. In important places where this principle is violated, the Rationale points out a QUIET CHANGE.

  5. A standard is a treaty between implementor and programmer. Some numerical limits have been added to the Standard to give both implementors and programmers a better understanding of what must be provided by an implementation, of what can be expected and depended upon to exist. These limits are presented as minimum maxima (i.e., lower limits placed on the values of upper limits specified by an implementation) with the understanding that any implementor is at liberty to provide higher limits than the Standard mandates. Any program that takes advantage of these more tolerant limits is not strictly conforming, however, since other implementations are at liberty to enforce the mandated limits.

  6. Keep the spirit of C. The Committee kept as a major goal to preserve the traditional spirit of C. There are many facets of the spirit of C, but the essence is a community sentiment of the underlying principles upon which the C language is based. Some of the facets of the spirit of C can be summarized in phrases like

  (a) Trust the programmer.

  (b) Don't prevent the programmer from doing what needs to be done.

  (c) Keep the language small and simple.

  (d) Provide only one way to do an operation.

  (e) Make it fast, even if it is not guaranteed to be portable.

  The last proverb needs a little explanation. The potential for efficient code generation is one of the most important strengths of C. To help ensure that no code explosion occurs for what appears to be a very simple operation, many operations are defined to be how the target machine's hardware does it rather than by a general abstract rule. An example of this willingness to live with what the machine does can be seen in the rules that govern the widening of char objects for use in expressions: whether the values of char objects widen to signed or unsigned quantities typically depends on which byte operation is more efficient on the target machine.

  One of the goals of the Committee was to avoid interfering with the ability of translators to generate compact, efficient code. In several cases the Committee has introduced features to improve the possible efficiency of the generated code; for instance, floating point operations may be performed in single-precision if both operands are float rather than double.

  Additional Principles

  At the WG14 meeting in Tokyo, Japan, in July 1994, the original principles were re-endorsed and the following new ones were added:

  7. Support international programming. During the initial standardization process, support for internationalization was something of an afterthought. Now that internationalization has proved to be an important topic it should have equal visibility with other topics. As a result, all revision proposals submitted shall be reviewed with regard to their impact on internationalization as well as for other technical merit.

  8. Codify existing practice to address evident deficiencies. Only those concepts that have some prior art should be accepted. (Prior art may come from implementations of languages other than C.) Unless some proposed new feature addresses an evident deficiency that is actually felt by more than a few C programmers, no new inventions should be entertained.

  9. Minimize incompatibilities with C90 (ISO/IEC 9899:1990). It should be possible for existing C implementations to gradually migrate to future conformance, rather than requiring a replacement of the environment. It should also be possible for the vast majority of existing conforming C programs to run unchanged.

  10. Minimize incompatibilities with C++. The committee recognizes the need for a clear and defensible plan with regard to how it intends to address the compatibility issue with C++. The committee endorses the principle of maintaining the largest common subset clearly and from the outset. Such a principle should satisfy the requirement to maximize overlap of the languages while maintaining a distinction between them and allowing them to evolve separately.

  Regarding our relationship with C++, the committee is content to let C++ be the ``big'' and ambitious language. While some features of C++ may well be embraced, it is not the committee's intention that C become C++.

  11. Maintain conceptual simplicity. The committee prefers an economy of concepts that do the job. Members should identify the issues and prescribe the minimal amount of machinery that will solve them. The committee recognizes the importance of being able to describe and teach new concepts in a straightforward and concise manner.
   

• Project status and milestones Work Item 9899 - Programming Language C
  Milestones:         1998-08   FCD sent for ballot.
                      1999-03   FDIS to be sent for ballot.
                      1999-12   International standard 9899 published
   

• [Feb 24, 2001] kuro5hin.org Are you Ready For C99

  ANSI and the ISO ratified the newest draft of the C standard in 1999 and unleashed the biggest changes to the language to date. New keywords, library functions, and macros are just the tip of the iceberg when it comes to the new improved C. In fact, the language is so different it is no longer compatible with C++. This article attempts to give an overview of the major changes made to the C language and also attempts to discover why no one yet seems to be affected by the new standard.

• Dennis Ritchie's opinion of the C99 standard
• Using the GNU Compiler Collection (GCC)

  For each language compiled by GCC for which there is a standard, GCC attempts to follow one or more versions of that standard, possibly with some exceptions, and possibly with some extensions.

  GCC supports three versions of the C standard, although support for the most recent version is not yet complete.

  The original ANSI C standard (X3.159-1989) was ratified in 1989 and published in 1990. This standard was ratified as an ISO standard (ISO/IEC 9899:1990) later in 1990. There were no technical differences between these publications, although the sections of the ANSI standard were renumbered and became clauses in the ISO standard. This standard, in both its forms, is commonly known as C89, or occasionally as C90, from the dates of ratification. The ANSI standard, but not the ISO standard, also came with a Rationale document. To select this standard in GCC, use one of the options -ansi, -std=c89 or -std=iso9899:1990; to obtain all the diagnostics required by the standard, you should also specify -pedantic (or -pedantic-errors if you want them to be errors rather than warnings). See Options Controlling C Dialect.

  Errors in the 1990 ISO C standard were corrected in two Technical Corrigenda published in 1994 and 1996. GCC does not support the uncorrected version.

  An amendment to the 1990 standard was published in 1995. This amendment added digraphs and __STDC_VERSION__ to the language, but otherwise concerned the library. This amendment is commonly known as AMD1; the amended standard is sometimes known as C94 or C95. To select this standard in GCC, use the option -std=iso9899:199409 (with, as for other standard versions, -pedantic to receive all required diagnostics).

  A new edition of the ISO C standard was published in 1999 as ISO/IEC 9899:1999, and is commonly known as C99. GCC has incomplete support for this standard version; see http://gcc.gnu.org/c99status.html for details. To select this standard, use -std=c99 or -std=iso9899:1999. (While in development, drafts of this standard version were referred to as C9X.)

  Errors in the 1999 ISO C standard were corrected in a Technical Corrigendum published in 2001. GCC does not support the uncorrected version.

  By default, GCC provides some extensions to the C language that on rare occasions conflict with the C standard. See Extensions to the C Language Family. Use of the -std options listed above will disable these extensions where they conflict with the C standard version selected. You may also select an extended version of the C language explicitly with -std=gnu89 (for C89 with GNU extensions) or -std=gnu99 (for C99 with GNU extensions). The default, if no C language dialect options are given, is -std=gnu89; this will change to -std=gnu99 in some future release when the C99 support is complete. Some features that are part of the C99 standard are accepted as extensions in C89 mode.

  The ISO C standard defines (in clause 4) two classes of conforming implementation. A conforming hosted implementation supports the whole standard including all the library facilities; a conforming freestanding implementation is only required to provide certain library facilities: those in <float.h>, <limits.h>, <stdarg.h>, and <stddef.h>; since AMD1, also those in <iso646.h>; and in C99, also those in <stdbool.h> and <stdint.h>. In addition, complex types, added in C99, are not required for freestanding implementations. The standard also defines two environments for programs, a freestanding environment, required of all implementations and which may not have library facilities beyond those required of freestanding implementations, where the handling of program startup and termination are implementation-defined, and a hosted environment, which is not required, in which all the library facilities are provided and startup is through a function int main (void) or int main (int, char *[]). An OS kernel would be a freestanding environment; a program using the facilities of an operating system would normally be in a hosted implementation.

  GCC aims towards being usable as a conforming freestanding implementation, or as the compiler for a conforming hosted implementation. By default, it will act as the compiler for a hosted implementation, defining __STDC_HOSTED__ as 1 and presuming that when the names of ISO C functions are used, they have the semantics defined in the standard. To make it act as a conforming freestanding implementation for a freestanding environment, use the option -ffreestanding; it will then define __STDC_HOSTED__ to 0 and not make assumptions about the meanings of function names from the standard library. To build an OS kernel, you may well still need to make your own arrangements for linking and startup. See Options Controlling C Dialect.

  GCC does not provide the library facilities required only of hosted implementations, nor yet all the facilities required by C99 of freestanding implementations; to use the facilities of a hosted environment, you will need to find them elsewhere (for example, in the GNU C library). See Standard Libraries.

BCPL

• Clive Feather gives a brief introduction to BCPL

• Alan Watson on BCPL

Etc

Society

Groupthink : Two Party System as Polyarchy : Corruption of Regulators : Bureaucracies : Understanding Micromanagers and Control Freaks : Toxic Managers :   Harvard Mafia : Diplomatic Communication : Surviving a Bad Performance Review : Insufficient Retirement Funds as Immanent Problem of Neoliberal Regime : PseudoScience : Who Rules America : Neoliberalism  : The Iron Law of Oligarchy : Libertarian Philosophy

Quotes

War and Peace : Skeptical Finance : John Kenneth Galbraith :Talleyrand : Oscar Wilde : Otto Von Bismarck : Keynes : George Carlin : Skeptics : Propaganda  : SE quotes : Language Design and Programming Quotes : Random IT-related quotes :  Somerset Maugham : Marcus Aurelius : Kurt Vonnegut : Eric Hoffer : Winston Churchill : Napoleon Bonaparte : Ambrose Bierce :  Bernard Shaw : Mark Twain Quotes

Bulletin:

Vol 25, No.12 (December, 2013) Rational Fools vs. Efficient Crooks The efficient markets hypothesis : Political Skeptic Bulletin, 2013 : Unemployment Bulletin, 2010 :  Vol 23, No.10 (October, 2011) An observation about corporate security departments : Slightly Skeptical Euromaydan Chronicles, June 2014 : Greenspan legacy bulletin, 2008 : Vol 25, No.10 (October, 2013) Cryptolocker Trojan (Win32/Crilock.A) : Vol 25, No.08 (August, 2013) Cloud providers as intelligence collection hubs : Financial Humor Bulletin, 2010 : Inequality Bulletin, 2009 : Financial Humor Bulletin, 2008 : Copyleft Problems Bulletin, 2004 : Financial Humor Bulletin, 2011 : Energy Bulletin, 2010 : Malware Protection Bulletin, 2010 : Vol 26, No.1 (January, 2013) Object-Oriented Cult : Political Skeptic Bulletin, 2011 : Vol 23, No.11 (November, 2011) Softpanorama classification of sysadmin horror stories : Vol 25, No.05 (May, 2013) Corporate bullshit as a communication method  : Vol 25, No.06 (June, 2013) A Note on the Relationship of Brooks Law and Conway Law

History:

Fifty glorious years (1950-2000): the triumph of the US computer engineering : Donald Knuth : TAoCP and its Influence of Computer Science : Richard Stallman : Linus Torvalds  : Larry Wall  : John K. Ousterhout : CTSS : Multix OS Unix History : Unix shell history : VI editor : History of pipes concept : Solaris : MS DOS :  Programming Languages History : PL/1 : Simula 67 : C : History of GCC development :  Scripting Languages : Perl history   : OS History : Mail : DNS : SSH : CPU Instruction Sets : SPARC systems 1987-2006 : Norton Commander : Norton Utilities : Norton Ghost : Frontpage history : Malware Defense History : GNU Screen : OSS early history

Classic books:

The Peter Principle : Parkinson Law : 1984 : The Mythical Man-Month :  How to Solve It by George Polya : The Art of Computer Programming : The Elements of Programming Style : The Unix Hater’s Handbook : The Jargon file : The True Believer : Programming Pearls : The Good Soldier Svejk : The Power Elite

Most popular humor pages:

Manifest of the Softpanorama IT Slacker Society : Ten Commandments of the IT Slackers Society : Computer Humor Collection : BSD Logo Story : The Cuckoo's Egg : IT Slang : C++ Humor : ARE YOU A BBS ADDICT? : The Perl Purity Test : Object oriented programmers of all nations : Financial Humor : Financial Humor Bulletin, 2008 : Financial Humor Bulletin, 2010 : The Most Comprehensive Collection of Editor-related Humor : Programming Language Humor : Goldman Sachs related humor : Greenspan humor : C Humor : Scripting Humor : Real Programmers Humor : Web Humor : GPL-related Humor : OFM Humor : Politically Incorrect Humor : IDS Humor : "Linux Sucks" Humor : Russian Musical Humor : Best Russian Programmer Humor : Microsoft plans to buy Catholic Church : Richard Stallman Related Humor : Admin Humor : Perl-related Humor : Linus Torvalds Related humor : PseudoScience Related Humor : Networking Humor : Shell Humor : Financial Humor Bulletin, 2011 : Financial Humor Bulletin, 2012 : Financial Humor Bulletin, 2013 : Java Humor : Software Engineering Humor : Sun Solaris Related Humor : Education Humor : IBM Humor : Assembler-related Humor : VIM Humor : Computer Viruses Humor : Bright tomorrow is rescheduled to a day after tomorrow : Classic Computer Humor

The Last but not Least Technology is dominated by two types of people: those who understand what they do not manage and those who manage what they do not understand ~Archibald Putt. Ph.D

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Last modified: March 12, 2019