How do I use CMake ExternalProject_Add or alternatives in a cross-platform way?

Question

Problems

-DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}

This is enough for single-configuration projects. But for Xcode and Visual Studio, you need to set CMAKE_CONFIGURATION_TYPES plus call build . --config at the build stage. See my answer.

COMMAND cd <BINARY_DIR> && make install

This will work only for Makefile generators of course. To be cross-platform you can use:

--build . --target install --config inside INSTALL_COMMAND of ExternalProject_Add.

Take a look at this template file, and in particular the following lines:

ExternalProject_Add(
    "${current_project}"
    URL
    @HUNTER_PACKAGE_URL@
    URL_HASH
    SHA1=@HUNTER_PACKAGE_SHA1@
    DOWNLOAD_DIR
    "@HUNTER_PACKAGE_DOWNLOAD_DIR@"
    SOURCE_DIR
    "@HUNTER_PACKAGE_SOURCE_DIR@"
    INSTALL_DIR
    "@HUNTER_PACKAGE_INSTALL_PREFIX@"
        # Not used, just avoid creating Install/<name> empty directory
    BUILD_COMMAND ""
        # This command is empty because all necessary targets will
        # be built on install stage
    CMAKE_ARGS
    "-G@CMAKE_GENERATOR@"
    "-C@HUNTER_CACHE_FILE@"
    "-C@HUNTER_ARGS_FILE@"
    "-D${postfix_name}=${${postfix_name}}"
    "-DCMAKE_BUILD_TYPE=${configuration}"
    "-DCMAKE_CONFIGURATION_TYPES=${configuration}"
    "-DCMAKE_INSTALL_PREFIX=@HUNTER_PACKAGE_INSTALL_PREFIX@"
    "-DCMAKE_TOOLCHAIN_FILE=${CMAKE_TOOLCHAIN_FILE}"
    INSTALL_COMMAND
        "@CMAKE_COMMAND@"
        --build .
        --target install
        --config ${configuration}
        --
        ${jobs_option}
)

Alternative

or is there a better alternative?

Have you seen Hunter?

You can add zlib just like this:

hunter_add_package(ZLIB)
find_package(ZLIB CONFIG REQUIRED)
target_link_libraries(... ZLIB::zlib)

This code works everywhere. Third party dependencies will be downloaded automatically in the configuration step. Example of building with different generator/toolchains (build.py is just a CMake wrapper that sets CMAKE_TOOLCHAIN_FILE and -G/-B):

build.py --toolchain mingw --config Release # MinGW Makefiles
build.py --toolchain vs-12-2013 --config Debug # Visual Studio 12 2013
build.py --toolchain xcode --config Release # Xcode
build.py --toolchain libcxx --config Release # Makefile with -stdlib=libc++ toolchain
build.py --toolchain ios-8-2 --config Release # Xcode with iOS SDK 8.2 toolchain

You got full control what options, build types or number of jobs you want to have while building third-party packages. For instance, this is how you can build four types, Debug, Release, MinSizeRel, and RelWithDebInfo for zlib and link MinSizeRel to the current project:

> build.py --toolchain xcode --verbose --config MinSizeRel --fwd "HUNTER_CONFIGURATION_TYPES=Release;Debug;MinSizeRel;RelWithDebInfo"
/.../clang  /.../lib/libz-MinSizeRel.a ... -o /.../_builds/xcode/MinSizeRel/foo

> ls -la /.../.hunter/_Base/d1232c0/326318e/37e4682/Install/lib/libz*
   99056 /.../.hunter/_Base/d1232c0/326318e/37e4682/Install/lib/libz-MinSizeRel.a
  307872 /.../.hunter/_Base/d1232c0/326318e/37e4682/Install/lib/libz-RelWithDebInfo.a
  109536 /.../.hunter/_Base/d1232c0/326318e/37e4682/Install/lib/libz.a
  258904 /.../.hunter/_Base/d1232c0/326318e/37e4682/Install/lib/libzd.a