c99(1posix)
NAME
c99 --- compile standard C programs
SYNOPSIS
c99 [options...] pathname [[pathname] [I directory]
[L directory] [l library]]...
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 input
files referenced by pathname operands and l option-arguments 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 input files 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 Section 1.1.1.4,
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
POSIX.12008, Section 12.2, Utility Syntax Guidelines, except that:
* Options can be interspersed with operands.
* The order of specifying the L and l options, and the order of
specifying l options with respect to pathname operands 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.
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.
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.
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. If the I option is used to
specify a directory that is one of the usual places searched
by default, the results are unspecified. 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. If the L option is used to specify a
directory that is one of the usual places searched by
default, the results are unspecified. 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.
l library
Search the library named liblibrary.a. A library shall be
searched when its name is encountered, so the placement of a
l option 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.
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.
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.
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 POSIX.12008 has been removed
(stripped). If both g and s options are present, the action
taken is unspecified.
U name Remove any initial definition of name.
Multiple instances of the D, I, L, l, and U options can be
specified.
OPERANDS
The application shall ensure that at least one pathname operand is
specified. The following forms for pathname 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.
STDIN
Not used.
INPUT FILES
Each 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 POSIX.12008, 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 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. 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 pathname operand ending in .c (or possibly other
unspecified suffixes) is given, for each such file:
"%s:\n", <pathname>
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 pathname operand ending in .c (or possibly other unspecified
suffixes) is given, for each such file:
"%s:\n", <pathname>
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. If the pathname of an object file or executable file to be created by c99 resolves to an existing directory entry for a file that is not a regular file, it is unspecified whether c99 shall attempt to create the file or shall issue a diagnostic and exit with a non-zero exit status.
EXTENDED DESCRIPTION
Standard Libraries
The c99 utility shall recognize the following l options for standard
libraries:
l c This option shall make available all interfaces referenced in
the System Interfaces volume of POSIX.12008, with the
possible exception of those interfaces listed as residing in
<aio.h>, <arpa/inet.h>, <complex.h>, <fenv.h>, <math.h>,
<mqueue.h>, <netdb.h>, <net/if.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>, interfaces marked as optional in
<sys/mman.h>, interfaces marked as ADV (Advisory Information)
in <fcntl.h>, and interfaces beginning with the prefix clock_
or time_ in <time.h>. This option shall not be required to
be present to cause a search of this library.
l l This option shall make available all interfaces required by
the C-language output of lex that are not made available
through the l c option.
l pthread
This option shall make available all interfaces 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 option.
l m This option shall make available all interfaces referenced in
<math.h>, <complex.h>, and <fenv.h>. An implementation may
search this library in the absence of this option.
l rt This option shall make available all interfaces referenced in
<aio.h>, <mqueue.h>, <sched.h>, <semaphore.h>, and <spawn.h>,
interfaces marked as optional in <sys/mman.h>, interfaces
marked as ADV (Advisory Information) in <fcntl.h>, and
interfaces beginning with the prefix clock_ and time_ in
<time.h>. An implementation may search this library in the
absence of this option.
l trace This option shall make available all interfaces referenced in
<trace.h>. An implementation may search this library in the
absence of this option.
l xnet This option shall make available all interfaces referenced in
<arpa/inet.h>, <netdb.h>, <net/if.h>, <netinet/in.h>, and
<sys/socket.h>. An implementation may search this library in
the absence of this option.
l y This option shall make available all interfaces required by
the C-language output of yacc that are not made available
through the l c option.
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
option to be passed to the link editor after the last pathname operand
or l option, causing it to be searched after all other object files
and libraries are loaded.
It is unspecified whether the libraries libc.a, libl.a, libm.a,
libpthread.a, librt.a, libtrace.a, libxnet.a, or liby.a exist as
regular files. The implementation may accept as l option-arguments
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.
Header Search
If a file with the same name as one of the standard headers defined in
the Base Definitions volume of POSIX.12008, Chapter 13, Headers, not
provided as part of the implementation, is placed in any of the usual
places that are searched by default for headers, the results 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 4-4: Programming Environments: Type Sizes
Programming Environment Bits in Bits in Bits in Bits in
getconf Name int long pointer off_t
_POSIX_V7_ILP32_OFF32 32 32 32 32
_POSIX_V7_ILP32_OFFBIG 32 32 32 64
_POSIX_V7_LP64_OFF64 32 64 64 64
_POSIX_V7_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 ptrdiff_t tcflag_t
cc_t size_t wchar_t
mode_t speed_t wint_t
nfds_t ssize_t
pid_t suseconds_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 Table 4-4, 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_V7_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 except l
but before any operands or l options, and the appropriate libraries at
the end of the operands and l options.
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 4-5: Programming Environments: c99 Arguments
Programming Environment c99 Arguments
getconf Name Use getconf Name
_POSIX_V7_ILP32_OFF32 C Compiler Flags POSIX_V7_ILP32_OFF32_CFLAGS
Linker/Loader Flags POSIX_V7_ILP32_OFF32_LDFLAGS
Libraries POSIX_V7_ILP32_OFF32_LIBS
_POSIX_V7_ILP32_OFFBIG C Compiler Flags POSIX_V7_ILP32_OFFBIG_CFLAGS
Linker/Loader Flags POSIX_V7_ILP32_OFFBIG_LDFLAGS
Libraries POSIX_V7_ILP32_OFFBIG_LIBS
_POSIX_V7_LP64_OFF64 C Compiler Flags POSIX_V7_LP64_OFF64_CFLAGS
Linker/Loader Flags POSIX_V7_LP64_OFF64_LDFLAGS
Libraries POSIX_V7_LP64_OFF64_LIBS
_POSIX_V7_LPBIG_OFFBIG C Compiler Flags POSIX_V7_LPBIG_OFFBIG_CFLAGS
Linker/Loader Flags POSIX_V7_LPBIG_OFFBIG_LDFLAGS
Libraries POSIX_V7_LPBIG_OFFBIG_LIBS
In addition to the type size programming environments above, all
implementations also support a multi-threaded programming environment
that is orthogonal to all of the programming environments listed above.
The getconf utility can be used to get flags for the threaded
programming environment, as indicated in Table 4-6, Threaded
Programming Environment: c99 Arguments.
Table 4-6: Threaded Programming Environment: c99 Arguments
Programming Environment c99 Arguments
getconf Name Use getconf Name
_POSIX_THREADS C Compiler Flags POSIX_V7_THREADS_CFLAGS
Linker/Loader Flags POSIX_V7_THREADS_LDFLAGS
These programming environment flags may be used in conjunction with any
of the type size programming environments supported by the
implementation.
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 POSIX.12008, 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. 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 POSIX.12008 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. In the ISO C standard the mapping from physical source characters to the C source character set is implementation-defined. Implementations may strip white-space characters before the terminating <newline> of a (physical) line as part of this mapping and, as a consequence of this, one or more white-space characters (and no other characters) between a <backslash> character and the <newline> character that terminates the line produces implementation-defined results. Portable applications should not use such constructs. Some c99 compilers not conforming to POSIX.12008 do not support trigraphs by default.
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:
offbig_env=$(getconf _POSIX_V7_ILP32_OFFBIG)
if [ $offbig_env != "-1" ] && [ $offbig_env != "undefined" ]
then
c99 $(getconf POSIX_V7_ILP32_OFFBIG_CFLAGS) \
$(getconf POSIX_V7_THREADS_CFLAGS) -D_XOPEN_SOURCE=700 \
$(getconf POSIX_V7_ILP32_OFFBIG_LDFLAGS) \
$(getconf POSIX_V7_THREADS_LDFLAGS) foo.c -o foo \
$(getconf POSIX_V7_ILP32_OFFBIG_LIBS) \
-l pthread
else
echo ILP32_OFFBIG programming environment not supported
exit 1
fi
3. The following examples clarify the use and interactions of L and
l options.
Consider the case in which module a.c calls function f() in library
libQ.a, and module b.c calls function g() in library libp.a.
Assume that both libraries reside in /a/b/c. The command line to
compile and link in the desired way is:
c99 L /a/b/c main.o a.c l Q b.c l p
In this case the L option need only precede the first l option,
since both libQ.a and libp.a reside in the same directory.
Multiple L options can be used when library name collisions occur.
Building on the previous example, suppose that the user wants to
use a new libp.a, in /a/a/a, but still wants f() from
/a/b/c/libQ.a:
c99 L /a/a/a L /a/b/c main.o a.c l Q b.c l p
In this example, the linker searches the L options in the order
specified, and finds /a/a/a/libp.a before /a/b/c/libp.a when
resolving references for b.c. The order of the l options is still
important, however.
4. The following example shows how an application can use a
programming environment where the widths of the following types:
blksize_t, cc_t, mode_t, nfds_t, pid_t, ptrdiff_t, size_t, speed_t,
ssize_t, suseconds_t, tcflag_t, wchar_t, wint_t
are no greater than the width of type long:
# First choose one of the listed environments ...
# ... if there are no additional constraints, the first one will do:
CENV=$(getconf POSIX_V7_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_V7_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=200809L \
$(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 POSIX2:1993 standard. Some of the changes from c89 include the ability to intersperse options and operands (which many c89 implementations allowed despite it not being specified), the description of l as an option instead of an operand, and the modification to the contents of the Standard Libraries section to account for new headers and options; for example, <spawn.h> added to the description of l rt, and l trace added for the Tracing option. POSIX.12008 specifies that the c99 utility must be able to use regular files for *.o files and for a.out files. Implementations are free to overwrite existing files of other types when attempting to create object files and executable files, but are not required to do so. If something other than a regular file is specified and using it fails for any reason, c99 is required to issue a diagnostic message and exit with a non-zero exit status. But for some file types, the problem may not be noticed for a long time. For example, if a FIFO named a.out exists in the current directory, c99 may attempt to open a.out and will hang in the open() call until another process opens the FIFO for reading. Then c99 may write most of the a.out to the FIFO and fail when it tries to seek back close to the start of the file to insert a timestamp (FIFOs are not seekable files). The c99 utility is also allowed to issue a diagnostic immediately if it encounters an a.out or *.o file that is not a regular file. For portable use, applications should ensure that any a.out, o option-argument, or *.o files corresponding to any *.c files do not conflict with names already in use that are not regular files or symbolic links that point to regular files. On many systems, multi-threaded applications run in a programming environment that is distinct from that used by single-threaded applications. This multi-threaded programming environment (in addition to needing to specify l pthread at link time) may require additional flags to be set when headers are processed at compile time (D_REENTRANT being common). This programming environment is orthogonal to the type size programming environments discussed above and listed in Table 4-4, Programming Environments: Type Sizes. This version of the standard adds getconf utility calls to provide the C compiler flags and linker/loader flags needed to support multi-threaded applications. Note that on a system where single-threaded applications are a special case of a multi-threaded application, both of these getconf calls may return NULL strings; on other implementations both of these strings may be non-NULL strings. The C standardization committee invented trigraphs (e.g., "??!" to represent '|') to address character portability problems in development environments based on national variants of the 7-bit ISO/IEC 646:1991 standard character set. However, these environments were already obsolete by the time the first ISO C standard was published, and in practice trigraphs have not been used for their intended purpose, and usually are intended to have their original meaning in K&R C. For example, in practice a C-language source string like "What??!" is usually intended to end in two <question-mark> characters and an <exclamation-mark>, not in '|'.
FUTURE DIRECTIONS
None.
SEE ALSO
Section 1.1.1.4, File Read, Write, and Creation, ar, getconf, make, nm, strip, umask The Base Definitions volume of POSIX.12008, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines, Chapter 13, Headers The System Interfaces volume of POSIX.12008, exec, sysconf()
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html . Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .
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