In my last post I explained how I recently extended my build to support multiple platforms using CMake. During this process, there were several tasks that required some Googling (as the CMake documentation can be a bit hard to chew). I thought it would be useful to combine all of these little tips into a single post. Enjoy!

Adding a Directory to your Header Search Paths

To add a header search path, use the include_directories command. For example:

include_directories( ../external/boost/ )

Adding a Directory to your Library Search Paths

Same syntax as above, but use the link_directories command instead:

link_directories( ../external/libcinder/libs/ )

Linking To Third-Party Libraries

To link to a third-party library, you first need to add the library to your project as if it were a library you are building yourself. You can do this with the add_library command:

add_library( libcinder STATIC IMPORTED )

The third argument is the most important here - it tells CMake that this library is pre-built, and that there are therefore no sources to specify.

Once you’ve defined the library, you then have to tell CMake where the prebuilt library is located. This can be done by setting the IMPORTED_LOCATION property on your new library:

set_property( TARGET libcinder PROPERTY IMPORTED_LOCATION libcinder.a )

Now that you have defined your library, you can then have your executable target it by using the target_link_libraries command:

add_executable( AwesomeDemo ${ SOURCE_FILES } )
target_link_libraries( AwesomeDemo libcinder )

Specifying Different Debug and Release Libraries

Is is pretty likely that your third-party vendor has supplied different debug and release builds of their libraries. Here is an example of how to express this in CMake:

add_library( libcinder_d STATIC IMPORTED )
add_library( libcinder STATIC IMPORTED )

set_property( TARGET libcinder_d PROPERTY IMPORTED_LOCATION libcinder_d.a )
set_property( TARGET libcinder PROPERTY IMPORTED_LOCATION libcinder.a )

add_executable( AwesomeDemo ${ SOURCE_FILES } )
target_link_libraries( AwesomeDemo debug libcinder_d optimized libcinder )

What we’ve basically done here is define both external libraries. Then, when calling the target_link_libraries command we can use the debug and optimized keywords to specify the two versions accordingly.

How To Access Environment Variables

Environment variables can be accessed via the ENV CMake variable, for example:

include_directories( $ENV{ MAYA_PATH }/devkit/include )

How to detect Apple, Windows, and Linux

If you need to add platform specific commands to your CMakeLists then you can use the following syntax:

    # Add your apple commands here

IF (WIN32)
    # Add your windows commands here

    # Add your unix commands here

How to force i386 architecture on Apple Builds

By default, CMake targets the architecture that you are running on. This means that if you’re running on a 64-bit Intel CPU, your target architecture will be set to x86_64. Some external libraries don’t support 64-bit processors, in which case you need to find a way of forcing CMake to target 32-bit architectures only. This can controlled via the CMAKE_OSX_ARCHITECTURES environment variable. This environment variable takes a comma separated list of all the architectures you want to target. So, to force CMake to target 32-bit Intel chips, you would set CMAKE_OSX_ARCHITECTURES to i386.

How to build an executable project as an Apple app bundle

On Apple, by default the add_executable command will build an executable as a command line tool. In order to build the executable as an app bundle, use the MACOSX_BUNDLE keyword:

add_executable( AwesomeDemo MACOSX_BUNDLE ${ SOURCE_FILES } )