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6.4.1 Running Test Programs

Use the following macro if you need to test run-time behavior of the system while configuring.

Macro: AC_TRY_RUN (program, [action-if-true], [action-if-false], [action-if-cross-compiling])
If program compiles and links successfully and returns an exit status of 0 when executed, run shell commands action-if-true. Otherwise, run shell commands action-if-false.

This macro double quotes program, the text of a program in the current language (see section 6.7 Language Choice), on which shell variable and back quote substitutions are performed. This macro uses CFLAGS or CXXFLAGS, CPPFLAGS, LDFLAGS, and LIBS when compiling.

If the C compiler being used does not produce executables that run on the system where configure is being run, then the test program is not run. If the optional shell commands action-if-cross-compiling are given, they are run instead. Otherwise, configure prints an error message and exits.

In the action-if-false section, the exit status of the program is available in the shell variable `$?', but be very careful to limit yourself to positive values smaller than 127; bigger values shall be saved into a file by the program. Note also that you have simply no guarantee that this exit status is issued by the program, or by the failure of its compilation. In other words, use this feature if sadist only, it was reestablished because the Autoconf maintainers grew tired of receiving "bug reports".

Try to provide a pessimistic default value to use when cross-compiling makes run-time tests impossible. You do this by passing the optional last argument to AC_TRY_RUN. autoconf prints a warning message when creating configure each time it encounters a call to AC_TRY_RUN with no action-if-cross-compiling argument given. You may ignore the warning, though users will not be able to configure your package for cross-compiling. A few of the macros distributed with Autoconf produce this warning message.

To configure for cross-compiling you can also choose a value for those parameters based on the canonical system name (see section 11. Manual Configuration). Alternatively, set up a test results cache file with the correct values for the host system (see section 7.3 Caching Results).

To provide a default for calls of AC_TRY_RUN that are embedded in other macros, including a few of the ones that come with Autoconf, you can call AC_PROG_CC before running them. Then, if the shell variable cross_compiling is set to `yes', use an alternate method to get the results instead of calling the macros.

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