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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, @ovar{action-if-true}, @ovar{action-if-false}, @ovar{action-if-cross-compiling})

program is the text of a C program, on which shell variable and back quote substitutions are performed. If it 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; the exit status of the program is available in the shell variable `$?'. 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.

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 Manual Configuration). Alternatively, set up a test results cache file with the correct values for the host system (see section 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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