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(autoconf.info)System Services

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System Services
===============

   The following macros check for operating system services or
capabilities.

 - Macro: AC_CYGWIN
     Checks for the Cygwin environment.  If present, sets shell variable
     `CYGWIN' to `yes'.  If not present, sets `CYGWIN' to the empty
     string.

 - Macro: AC_EXEEXT
     Defines substitute variable `EXEEXT' based on the output of the
     compiler, after .c, .o, and .obj files have been excluded.
     Typically set to empty string if Unix, `.exe' or `.EXE' if Win32.

 - Macro: AC_OBJEXT
     Defines substitute variable `OBJEXT' based on the output of the
     compiler, after .c files have been excluded.  Typically set to
     `.o' if Unix, `.obj' if Win32.

 - Macro: AC_MINGW32
     Checks for the MingW32 compiler environment.  If present, sets
     shell variable `MINGW32' to `yes'.  If not present, sets `MINGW32'
     to the empty string.

 - Macro: AC_PATH_X
     Try to locate the X Window System include files and libraries.  If
     the user gave the command line options `--x-includes=DIR' and
     `--x-libraries=DIR', use those directories.  If either or both
     were not given, get the missing values by running `xmkmf' on a
     trivial `Imakefile' and examining the `Makefile' that it produces.
     If that fails (such as if `xmkmf' is not present), look for them
     in several directories where they often reside.  If either method
     is successful, set the shell variables `x_includes' and
     `x_libraries' to their locations, unless they are in directories
     the compiler searches by default.

     If both methods fail, or the user gave the command line option
     `--without-x', set the shell variable `no_x' to `yes'; otherwise
     set it to the empty string.

 - Macro: AC_PATH_XTRA
     An enhanced version of `AC_PATH_X'.  It adds the C compiler flags
     that X needs to output variable `X_CFLAGS', and the X linker flags
     to `X_LIBS'.  If X is not available, adds `-DX_DISPLAY_MISSING' to
     `X_CFLAGS'.

     This macro also checks for special libraries that some systems
     need in order to compile X programs.  It adds any that the system
     needs to output variable `X_EXTRA_LIBS'.  And it checks for
     special X11R6 libraries that need to be linked with before
     `-lX11', and adds any found to the output variable `X_PRE_LIBS'.


 - Macro: AC_SYS_INTERPRETER
     Check whether the system supports starting scripts with a line of
     the form `#! /bin/csh' to select the interpreter to use for the
     script.  After running this macro, shell code in `configure.in'
     can check the shell variable `interpval'; it will be set to `yes'
     if the system supports `#!', `no' if not.

 - Macro: AC_SYS_LONG_FILE_NAMES
     If the system supports file names longer than 14 characters, define
     `HAVE_LONG_FILE_NAMES'.

 - Macro: AC_SYS_RESTARTABLE_SYSCALLS
     If the system automatically restarts a system call that is
     interrupted by a signal, define `HAVE_RESTARTABLE_SYSCALLS'.