C99 - The Open Group Publications Catalog

The Open Group Base Specifications Issue 6 IEEE Std 1003.1, 2004 Edition Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.A newer edition of this document exists here

NAME

c99 - compile standard C programs

SYNOPSIS

[CD] c99 [-c][-D name[=value]]...[-E][-g][-I directory] ... [-L directory] ... [-o outfile][-Ooptlevel][-s][-U name]... operand ...

DESCRIPTION

The c99 utility is an interface to the standard C compilation system; it shall accept source code conforming to the ISO C standard. The system conceptually consists of a compiler and link editor. The files referenced by operands shall be compiled and linked to produce an executable file. (It is unspecified whether the linking occurs entirely within the operation of c99; some implementations may produce objects that are not fully resolved until the file is executed.)

If the -c option is specified, for all pathname operands of the form file .c, the files:

$(basename pathname .c).o

shall be created as the result of successful compilation. If the -c option is not specified, it is unspecified whether such .o files are created or deleted for the file .c operands.

If there are no options that prevent link editing (such as -c or -E), and all operands compile and link without error, the resulting executable file shall be written according to the -o outfile option (if present) or to the file a.out.

The executable file shall be created as specified in File Read, Write, and Creation , except that the file permission bits shall be set to:

S_IRWXO | S_IRWXG | S_IRWXU

and the bits specified by the umask of the process shall be cleared.

OPTIONS

The c99 utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines, except that:

• The -l library operands have the format of options, but their position within a list of operands affects the order in which libraries are searched.

• The order of specifying the -I and -L options is significant.

• Conforming applications shall specify each option separately; that is, grouping option letters (for example, -cO) need not be recognized by all implementations.

The following options shall be supported:

-c Suppress the link-edit phase of the compilation, and do not remove any object files that are produced. -g Produce symbolic information in the object or executable files; the nature of this information is unspecified, and may be modified by implementation-defined interactions with other options. -s Produce object or executable files, or both, from which symbolic and other information not required for proper execution using the exec family defined in the System Interfaces volume of IEEE Std 1003.1-2001 has been removed (stripped). If both -g and -s options are present, the action taken is unspecified. -o outfile Use the pathname outfile, instead of the default a.out, for the executable file produced. If the -o option is present with -c or -E, the result is unspecified. -D name[=value] Define name as if by a C-language #define directive. If no = value is given, a value of 1 shall be used. The -D option has lower precedence than the -U option. That is, if name is used in both a -U and a -D option, name shall be undefined regardless of the order of the options. Additional implementation-defined names may be provided by the compiler. Implementations shall support at least 2048 bytes of -D definitions and 256 names. -E Copy C-language source files to standard output, expanding all preprocessor directives; no compilation shall be performed. If any operand is not a text file, the effects are unspecified. -I directory Change the algorithm for searching for headers whose names are not absolute pathnames to look in the directory named by the directory pathname before looking in the usual places. Thus, headers whose names are enclosed in double-quotes ( "" ) shall be searched for first in the directory of the file with the #include line, then in directories named in -I options, and last in the usual places. For headers whose names are enclosed in angle brackets ( "<>" ), the header shall be searched for only in directories named in -I options and then in the usual places. Directories named in -I options shall be searched in the order specified. Implementations shall support at least ten instances of this option in a single c99 command invocation. -L directory Change the algorithm of searching for the libraries named in the -l objects to look in the directory named by the directory pathname before looking in the usual places. Directories named in -L options shall be searched in the order specified. Implementations shall support at least ten instances of this option in a single c99 command invocation. If a directory specified by a -L option contains files with names starting with any of the strings "libc.", "libl.", "libpthread.", "libm.", "librt.", "libtrace.", "libxnet.", or "liby.", the results are unspecified. -O optlevel Specify the level of code optimization. If the optlevel option-argument is the digit '0', all special code optimizations shall be disabled. If it is the digit '1', the nature of the optimization is unspecified. If the -O option is omitted, the nature of the system's default optimization is unspecified. It is unspecified whether code generated in the presence of the -O 0 option is the same as that generated when -O is omitted. Other optlevel values may be supported. -U name Remove any initial definition of name.

Multiple instances of the -D, -I, -U, and -L options can be specified.

OPERANDS

An operand is either in the form of a pathname or the form -l library. The application shall ensure that at least one operand of the pathname form is specified. The following operands shall be supported:

file.c A C-language source file to be compiled and optionally linked. The application shall ensure that the operand is of this form if the -c option is used. file.a A library of object files typically produced by the ar utility, and passed directly to the link editor. Implementations may recognize implementation-defined suffixes other than .a as denoting object file libraries. file.o An object file produced by c99 -c and passed directly to the link editor. Implementations may recognize implementation-defined suffixes other than .o as denoting object files.

The processing of other files is implementation-defined.

-l library (The letter ell.) Search the library named: liblibrary.a

A library shall be searched when its name is encountered, so the placement of a -l operand is significant. Several standard libraries can be specified in this manner, as described in the EXTENDED DESCRIPTION section. Implementations may recognize implementation-defined suffixes other than .a as denoting libraries.

STDIN

Not used.

INPUT FILES

The input file shall be one of the following: a text file containing a C-language source program, an object file in the format produced by c99 -c, or a library of object files, in the format produced by archiving zero or more object files, using ar. Implementations may supply additional utilities that produce files in these formats. Additional input file formats are implementation-defined.

ENVIRONMENT VARIABLES

The following environment variables shall affect the execution of c99:

LANG Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.) LC_ALL If set to a non-empty string value, override the values of all the other internationalization variables. LC_CTYPE Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments and input files). LC_MESSAGES Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error. NLSPATH [XSI] Determine the location of message catalogs for the processing of LC_MESSAGES . TMPDIR Provide a pathname that should override the default directory for temporary files, if any. [XSI] On XSI-conforming systems, provide a pathname that shall override the default directory for temporary files, if any.

ASYNCHRONOUS EVENTS

Default.

STDOUT

If more than one file operand ending in .c (or possibly other unspecified suffixes) is given, for each such file:

"%s:\n", <file>

may be written. These messages, if written, shall precede the processing of each input file; they shall not be written to the standard output if they are written to the standard error, as described in the STDERR section.

If the -E option is specified, the standard output shall be a text file that represents the results of the preprocessing stage of the language; it may contain extra information appropriate for subsequent compilation passes.

STDERR

The standard error shall be used only for diagnostic messages. If more than one file operand ending in .c (or possibly other unspecified suffixes) is given, for each such file:

"%s:\n", <file>

may be written to allow identification of the diagnostic and warning messages with the appropriate input file. These messages, if written, shall precede the processing of each input file; they shall not be written to the standard error if they are written to the standard output, as described in the STDOUT section.

This utility may produce warning messages about certain conditions that do not warrant returning an error (non-zero) exit value.

OUTPUT FILES

Object files or executable files or both are produced in unspecified formats.

EXTENDED DESCRIPTION

Standard Libraries

The c99 utility shall recognize the following -l operands for standard libraries:

-l c This operand shall make visible all functions referenced in the System Interfaces volume of IEEE Std 1003.1-2001, with the possible exception of those functions listed as residing in <aio.h>, <arpa/inet.h>, <complex.h>, <fenv.h>, <math.h>, <mqueue.h>, <netdb.h>, <netinet/in.h>, <pthread.h>, <sched.h>, <semaphore.h>, <spawn.h>, <sys/socket.h>, pthread_kill(), and pthread_sigmask() in <signal.h>, <trace.h>, functions marked as extensions other than as part of the MF or MPR extensions in <sys/mman.h>, functions marked as ADV in <fcntl.h>, and functions marked as CS, CPT, and TMR in <time.h>. This operand shall not be required to be present to cause a search of this library. -l l This operand shall make visible all functions required by the C-language output of lex that are not made available through the -l c operand. -l pthread This operand shall make visible all functions referenced in <pthread.h> and pthread_kill() and pthread_sigmask() referenced in <signal.h>. An implementation may search this library in the absence of this operand. -l m This operand shall make visible all functions referenced in <math.h>, <complex.h>, and <fenv.h>. An implementation may search this library in the absence of this operand. -l rt This operand shall make visible all functions referenced in <aio.h>, <mqueue.h>, <sched.h>, <semaphore.h>, and <spawn.h>, functions marked as extensions other than as part of the MF or MPR extensions in <sys/mman.h>, functions marked as ADV in <fcntl.h>, and functions marked as CS, CPT, and TMR in <time.h>. An implementation may search this library in the absence of this operand. -l trace This operand shall make visible all functions referenced in <trace.h>. An implementation may search this library in the absence of this operand. -l xnet This operand makes visible all functions referenced in <arpa/inet.h>, <netdb.h>, <netinet/in.h>, and <sys/socket.h>. An implementation may search this library in the absence of this operand. -l y This operand shall make visible all functions required by the C-language output of yacc that are not made available through the -l c operand.

In the absence of options that inhibit invocation of the link editor, such as -c or -E, the c99 utility shall cause the equivalent of a -l c operand to be passed to the link editor as the last -l operand, causing it to be searched after all other object files and libraries are loaded.

It is unspecified whether the libraries libc.a, libm.a, librt.a, libpthread.a, libl.a, liby.a, or libxnet.a exist as regular files. The implementation may accept as -l operands names of objects that do not exist as regular files.

External Symbols

The C compiler and link editor shall support the significance of external symbols up to a length of at least 31 bytes; the action taken upon encountering symbols exceeding the implementation-defined maximum symbol length is unspecified.

The compiler and link editor shall support a minimum of 511 external symbols per source or object file, and a minimum of 4095 external symbols in total. A diagnostic message shall be written to the standard output if the implementation-defined limit is exceeded; other actions are unspecified.

Programming Environments

All implementations shall support one of the following programming environments as a default. Implementations may support more than one of the following programming environments. Applications can use sysconf() or getconf to determine which programming environments are supported.

Table: Programming Environments: Type Sizes

Programming Environment	Bits in	Bits in	Bits in	Bits in
getconf Name	int	long	pointer	off_t
_POSIX_V6_ILP32_OFF32	32	32	32	32
_POSIX_V6_ILP32_OFFBIG	32	32	32	>=64
_POSIX_V6_LP64_OFF64	32	64	64	64
_POSIX_V6_LPBIG_OFFBIG	>=32	>=64	>=64	>=64

All implementations shall support one or more environments where the widths of the following types are no greater than the width of type long:

blksize_t, cc_t, mode_t, nfds_t, pid_t, ptrdiff_t, size_t, speed_t, ssize_t, suseconds_t, tcflag_t, useconds_t, wchar_t, wint_t

The executable files created when these environments are selected shall be in a proper format for execution by the exec family of functions. Each environment may be one of the ones in Programming Environments: Type Sizes , or it may be another environment. The names for the environments that meet this requirement shall be output by a getconf command using the POSIX_V6_WIDTH_RESTRICTED_ENVS argument, as a <newline>-separated list of names suitable for use with the getconf -v option. If more than one environment meets the requirement, the names of all such environments shall be output on separate lines. Any of these names can then be used in a subsequent getconf command to obtain the flags specific to that environment with the following suffixes added as appropriate:

_CFLAGS To get the C compiler flags. _LDFLAGS To get the linker/loader flags. _LIBS To get the libraries.

This requirement may be removed in a future version.

When this utility processes a file containing a function called main(), it shall be defined with a return type equivalent to int. Using return from the initial call to main() shall be equivalent (other than with respect to language scope issues) to calling exit() with the returned value. Reaching the end of the initial call to main() shall be equivalent to calling exit(0). The implementation shall not declare a prototype for this function.

Implementations provide configuration strings for C compiler flags, linker/loader flags, and libraries for each supported environment. When an application needs to use a specific programming environment rather than the implementation default programming environment while compiling, the application shall first verify that the implementation supports the desired environment. If the desired programming environment is supported, the application shall then invoke c99 with the appropriate C compiler flags as the first options for the compile, the appropriate linker/loader flags after any other options but before any operands, and the appropriate libraries at the end of the operands.

Conforming applications shall not attempt to link together object files compiled for different programming models. Applications shall also be aware that binary data placed in shared memory or in files might not be recognized by applications built for other programming models.

Table: Programming Environments: c99 and cc Arguments

Programming Environment	c99 and cc Arguments
getconf Name	Use	getconf Name
_POSIX_V6_ILP32_OFF32	C Compiler Flags	POSIX_V6_ILP32_OFF32_CFLAGS
Linker/Loader Flags	POSIX_V6_ILP32_OFF32_LDFLAGS
Libraries	POSIX_V6_ILP32_OFF32_LIBS
_POSIX_V6_ILP32_OFFBIG	C Compiler Flags	POSIX_V6_ILP32_OFFBIG_CFLAGS
Linker/Loader Flags	POSIX_V6_ILP32_OFFBIG_LDFLAGS
Libraries	POSIX_V6_ILP32_OFFBIG_LIBS
_POSIX_V6_LP64_OFF64	C Compiler Flags	POSIX_V6_LP64_OFF64_CFLAGS
Linker/Loader Flags	POSIX_V6_LP64_OFF64_LDFLAGS
Libraries	POSIX_V6_LP64_OFF64_LIBS
_POSIX_V6_LPBIG_OFFBIG	C Compiler Flags	POSIX_V6_LPBIG_OFFBIG_CFLAGS
Linker/Loader Flags	POSIX_V6_LPBIG_OFFBIG_LDFLAGS
Libraries	POSIX_V6_LPBIG_OFFBIG_LIBS

EXIT STATUS

The following exit values shall be returned:

0 Successful compilation or link edit. >0 An error occurred.

CONSEQUENCES OF ERRORS

When c99 encounters a compilation error that causes an object file not to be created, it shall write a diagnostic to standard error and continue to compile other source code operands, but it shall not perform the link phase and return a non-zero exit status. If the link edit is unsuccessful, a diagnostic message shall be written to standard error and c99 exits with a non-zero status. A conforming application shall rely on the exit status of c99, rather than on the existence or mode of the executable file.

The following sections are informative.

APPLICATION USAGE

Since the c99 utility usually creates files in the current directory during the compilation process, it is typically necessary to run the c99 utility in a directory in which a file can be created.

On systems providing POSIX Conformance (see the Base Definitions volume of IEEE Std 1003.1-2001, Chapter 2, Conformance), c99 is required only with the C-Language Development option; XSI-conformant systems always provide c99.

Some historical implementations have created .o files when -c is not specified and more than one source file is given. Since this area is left unspecified, the application cannot rely on .o files being created, but it also must be prepared for any related .o files that already exist being deleted at the completion of the link edit.

Some historical implementations have permitted -L options to be interspersed with -l operands on the command line. For an application to compile consistently on systems that do not behave like this, it is necessary for a conforming application to supply all -L options before any of the -l options.

There is the possible implication that if a user supplies versions of the standard functions (before they would be encountered by an implicit -l c or explicit -l m), that those versions would be used in place of the standard versions. There are various reasons this might not be true (functions defined as macros, manipulations for clean name space, and so on), so the existence of files named in the same manner as the standard libraries within the -L directories is explicitly stated to produce unspecified behavior.

All of the functions specified in the System Interfaces volume of IEEE Std 1003.1-2001 may be made visible by implementations when the Standard C Library is searched. Conforming applications must explicitly request searching the other standard libraries when functions made visible by those libraries are used.

EXAMPLES

1. The following usage example compiles foo.c and creates the executable file foo:

   c99 -o foo foo.c

   The following usage example compiles foo.c and creates the object file foo.o:

   c99 -c foo.c

   The following usage example compiles foo.c and creates the executable file a.out:

   c99 foo.c

   The following usage example compiles foo.c, links it with bar.o, and creates the executable file a.out. It may also create and leave foo.o:

   c99 foo.c bar.o

2. The following example shows how an application using threads interfaces can test for support of and use a programming environment supporting 32-bit int, long, and pointer types and an off_t type using at least 64 bits:

   if [ $(getconf _POSIX_V6_ILP32_OFFBIG) != "-1" ] then c99 $(getconf POSIX_V6_ILP32_OFFBIG_CFLAGS) -D_XOPEN_SOURCE=600 \ $(getconf POSIX_V6_ILP32_OFFBIG_LDFLAGS) foo.c -o foo \ $(getconf POSIX_V6_ILP32_OFFBIG_LIBS) -l pthread else echo ILP32_OFFBIG programming environment not supported exit 1 fi

3. The following examples clarify the use and interactions of -L options and -l operands.

   Consider the case in which module a.c calls function f() in library libQ.a, and module b.c calls function g() in library libp.a. Assume that both libraries reside in /a/b/c. The command line to compile and link in the desired way is:

   c99 -L /a/b/c main.o a.c -l Q b.c -l p

   In this case the -l Q operand need only precede the first -l p operand, since both libQ.a and libp.a reside in the same directory.

   Multiple -L operands can be used when library name collisions occur. Building on the previous example, suppose that the user wants to use a new libp.a, in /a/a/a, but still wants f() from /a/b/c/libQ.a:

   c99 -L /a/a/a -L /a/b/c main.o a.c -l Q b.c -l p

   In this example, the linker searches the -L options in the order specified, and finds /a/a/a/libp.a before /a/b/c/libp.a when resolving references for b.c. The order of the -l operands is still important, however.

4. The following example shows how an application can use a programming environment where the widths of the following types:

   blksize_t, cc_t, mode_t, nfds_t, pid_t, ptrdiff_t, size_t, speed_t, ssize_t, suseconds_t, tcflag_t, useconds_t, wchar_t, wint_t

   are no greater than the width of type long:

   # First choose one of the listed environments ... # ... if there are no additional constraints, the first one will do: CENV=$(getconf POSIX_V6_WIDTH_RESTRICTED_ENVS | head -n l) # ... or, if an environment that supports large files is preferred, # look for names that contain "OFF64" or "OFFBIG". (This chooses # the last one in the list if none match.) for CENV in $(getconf POSIX_V6_WIDTH_RESTRICTED_ENVS) do case $CENV in *OFF64*|*OFFBIG*) break ;; esac done # The chosen environment name can now be used like this: c99 $(getconf ${CENV}_CFLAGS) -D _POSIX_C_SOURCE=200112L \ $(getconf ${CENV}_LDFLAGS) foo.c -o foo \ $(getconf ${CENV}_LIBS)

RATIONALE

The c99 utility is based on the c89 utility originally introduced in the ISO POSIX-2:1993 standard.

Some of the changes from c89 include the modification to the contents of the Standard Libraries section to account for new headers and options; for example, <spawn.h> added to the -l rt operand, and the -l trace operand added for the Tracing functions.

FUTURE DIRECTIONS

None.

SEE ALSO

File Read, Write, and Creation, ar, getconf, make, nm, strip, umask(), the System Interfaces volume of IEEE Std 1003.1-2001, exec, sysconf(), the Base Definitions volume of IEEE Std 1003.1-2001, Chapter 13, Headers

CHANGE HISTORY

First released in Issue 6. Included for alignment with the ISO/IEC 9899:1999 standard.

IEEE Std 1003.1-2001/Cor 1-2002, item XCU/TC1/D6/12 is applied, correcting the EXTENDED DESCRIPTION of -l c and -l m. Previously, the text did not take into account the presence of the c99 math headers.

IEEE Std 1003.1-2001/Cor 1-2002, item XCU/TC1/D6/13 is applied, changing the reference to the libxnet library to libxnet.a.

IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/5 is applied, updating the OPTIONS section, so that the names of files contained in the directory specified by the -L option are not assumed to end in the .a suffix. The set of library prefixes is also updated.

IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/6 is applied, removing the lead underscore from the POSIX_V6_WIDTH_RESTRICTED_ENVS variable in the EXTENDED DESCRIPTION and the EXAMPLES sections.

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