The following macros check for operating system services or capabilities.
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 (or an executable pointed to by the XMKMF
environment variable) on a trivial Imakefile and examining the
makefile that it produces. Setting XMKMF to ‘false’
disables this method.
If this method fails to find the X Window System, configure
looks for the files 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.
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. Define X_DISPLAY_MISSING if X is not
available.
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.
Check whether the system supports starting scripts with a line of the
form ‘#!/bin/sh’ to select the interpreter to use for the script.
After running this macro, shell code in configure.ac can check
the shell variable interpval; it is set to ‘yes’
if the system supports ‘#!’, ‘no’ if not.
If the default off_t type is a 32-bit integer,
and therefore cannot be used with files 2 GiB or larger,
make a wider off_t available if the system supports it.
Similarly, widen other types related to sizes of files and file systems
if possible. These types may include blkcnt_t, dev_t,
ino_t, fsblkcnt_t, fsfilcnt_t, and rlim_t.
Also, arrange for a configure option --enable-year2038
to request widening the type time_t as needed to represent file
wand other timestamps after mid-January 2038. This widening is possible
only on 32-bit GNU/Linux x86 and ARM systems with glibc 2.34 or later.
If year-2038 support is requested but configure fails to find a way
to widen time_t and inspection of the system suggests that
this feature is available somehow, configure will error out.
If you want the default to be --enable-year2038, you can use
AC_SYS_YEAR2038 or AC_SYS_YEAR2038_RECOMMENDED
instead of AC_SYS_LARGEFILE.
In other words, older packages that have long used AC_SYS_LARGEFILE
can have year-2038 support on 32-bit GNU/Linux x86 and ARM systems either by
regenerating configure with current Autoconf and configuring with
--enable-year2038, or by using AC_SYS_YEAR2038 or
AC_SYS_YEAR2038_RECOMMENDED and configuring without
--disable-year2038.
A future version of Autoconf might change the AC_SYS_LARGEFILE
default to --enable-year2038; if and when that happens,
AC_SYS_LARGEFILE and AC_SYS_YEAR2038 will become equivalent.
See AC_SYS_YEAR2038.
Set the shell variable ac_have_largefile to ‘yes’ or
no depending on whether a wide off_t is available,
regardless of whether arrangements were necessary.
Similarly, set the shell variable ac_have_year2038 to yes
or no depending on whether a wide-enough time_t is available.
Define preprocessor macros if necessary to make types wider;
for example, on GNU/Linux systems the macros _FILE_OFFSET_BITS
and _TIME_BITS can be defined. Some of these macros work only if
defined before the first system header is included;
therefore, when using this macro in concert with
AC_CONFIG_HEADERS, make sure that config.h is included
before any system headers.
On obsolete IRIX systems, also change the output variable CC to
add compiler options needed for wide off_t.
Large-file support can be disabled by configuring with the
--disable-largefile option, and year-2038 support can
be enabled and disabled via the --enable-year2038 and
--disable-year2038 options. These options have no effect on
systems where types are wide enough by default.
Large-file support is required for year-2038 support: if you configure
with --disable-largefile on a platform with 32-bit
time_t, then year-2038 support is not available.
Disabling large-file or year-2038 support can have surprising effects,
such as causing functions like readdir and stat to fail
even on a small file because its inode number or timestamp is out of range.
Regardless of whether you use this macro, portable programs should not
assume that any of the types listed above fit into a long int.
For example, it is not portable to print an arbitrary off_t or
time_t value X with printf ("%ld", (long int) X).
The standard C library functions fseek and ftell
do not use off_t. If you need to use either of these functions,
you should use AC_FUNC_FSEEKO as well as AC_SYS_LARGEFILE,
and then use their Posix replacements fseeko and ftello.
See AC_FUNC_FSEEKO.
When using AC_SYS_LARGEFILE in different packages that are linked
together and that have interfaces that depend on the width of off_t,
time_t or related types, the simplest thing is to configure all
components the same way. For example, if an application uses
AC_SYS_LARGEFILE and is configured with
--enable-year2038, libraries it links to with an off_t-
or time_t-dependent interface should be configured equivalently.
Alternatively, you can modify libraries to support both 32- and 64-bit
interfaces though this is more work and few libraries other than the C
library itself are modified in this way.
Applications and libraries should be configured compatibly.
If off_t, time_t or related types appear in a library’s
public interface, enabling or disabling the library’s large-file or
year-2038 support may break binary compatibility with applications or
with other libraries. Similarly, if an application links to a such a
library, enabling or disabling the application’s large-file support may
break binary compatibility with that library.
If the system supports file names longer than 14 characters, define
HAVE_LONG_FILE_NAMES.
Check to see if the Posix termios headers and functions are available on the
system. If so, set the shell variable ac_cv_sys_posix_termios to
‘yes’. If not, set the variable to ‘no’.
This is like AC_SYS_LARGEFILE except it defaults to enabling
instead of disabling year-2038 support. Year-2038 support for
applications and libraries should be configured compatibly.
See AC_SYS_LARGEFILE.
This macro has the same effect as AC_SYS_YEAR2038,
but also declares that the program being configured
should support timestamps after mid-January 2038.
If a large time_t is unavailable, configure will error
out unless the --disable-year2038 option is specified.
Year-2038 support for applications and libraries should be configured compatibly. See AC_SYS_YEAR2038.