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# try_run

Try compiling and then running some code.

    try_run(RUN_RESULT_VAR COMPILE_RESULT_VAR
            bindir srcfile [CMAKE_FLAGS <Flags>]
            [COMPILE_DEFINITIONS <flags>]
            [COMPILE_OUTPUT_VARIABLE comp]
            [RUN_OUTPUT_VARIABLE run]
            [OUTPUT_VARIABLE var]
            [ARGS <arg1> <arg2>...])

Try compiling a srcfile. Return TRUE or FALSE for success or failure in COMPILE_RESULT_VAR. Then if the compile succeeded, run the executable and return its exit code in RUN_RESULT_VAR. If the executable was built, but failed to run, then RUN_RESULT_VAR will be set to FAILED_TO_RUN. COMPILE_OUTPUT_VARIABLE specifies the variable where the output from the compile step goes. RUN_OUTPUT_VARIABLE specifies the variable where the output from the running executable goes.

For compatibility reasons OUTPUT_VARIABLE is still supported, which gives you the output from the compile and run step combined.

Cross compiling issues

When cross compiling, the executable compiled in the first step usually cannot be run on the build host. try_run() checks the CMAKE_CROSSCOMPILING variable to detect whether CMake is in crosscompiling mode. If that’s the case, it will still try to compile the executable, but it will not try to run the executable. Instead it will create cache variables which must be filled by the user or by presetting them in some CMake script file to the values the executable would have produced if it had been run on its actual target platform. These variables are RUN_RESULT_VAR (explanation see above) and if RUN_OUTPUT_VARIABLE (or OUTPUT_VARIABLE) was used, an additional cache variable RUN_RESULT_VAR__COMPILE_RESULT_VAR__TRYRUN_OUTPUT.This is intended to hold stdout and stderr from the executable.

In order to make cross compiling your project easier, use try_run only if really required. If you use try_run, use RUN_OUTPUT_VARIABLE (or OUTPUT_VARIABLE) only if really required. Using them will require that when crosscompiling, the cache variables will have to be set manually to the output of the executable. You can also “guard” the calls to try_run with if(CMAKE_CROSSCOMPILING) and provide an easy-to-preset alternative for this case.

Set variable CMAKE_TRY_COMPILE_CONFIGURATION to choose a build configuration.

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