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)
