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]]])

program is the text of a C program, on which shell variable and backquote 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 and this macro calls AC_C_CROSS if it has not already been called. 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 target 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_C_CROSS 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.

Macro: AC_C_CROSS

If the C compiler being used does not produce executables that can run on the system where configure is being run, set the shell variable cross_compiling to `yes', otherwise `no'. In other words, this tests whether the build system type is different from the host system type (the target system type is irrelevant to this test). See section Manual Configuration, for more on support for cross compiling.

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