Abseil Common Libraries (C++).zip

# Abseil CMake Build Instructions Abseil comes with a CMake build script ([CMakeLists.txt](../CMakeLists.txt)) that can be used on a wide range of platforms ("C" stands for cross-platform.). If you don't have CMake installed already, you can download it for free from <https://www.cmake.org/>. CMake works by generating native makefiles or build projects that can be used in the compiler environment of your choice. For API/ABI compatibility reasons, we strongly recommend building Abseil in a subdirectory of your project or as an embedded dependency. ## Incorporating Abseil Into a CMake Project The recommendations below are similar to those for using CMake within the googletest framework (<https://github.com/google/googletest/blob/master/googletest/README.md#incorporating-into-an-existing-cmake-project>) ### Step-by-Step Instructions 1. If you want to build the Abseil tests, integrate the Abseil dependency [Google Test](https://github.com/google/googletest) into your CMake project. To disable Abseil tests, you have to pass either `-DBUILD_TESTING=OFF` or `-DABSL_BUILD_TESTING=OFF` when configuring your project with CMake. 2. Download Abseil and copy it into a subdirectory in your CMake project or add Abseil as a [git submodule](https://git-scm.com/docs/git-submodule) in your CMake project. 3. You can then use the CMake command [`add_subdirectory()`](https://cmake.org/cmake/help/latest/command/add_subdirectory.html) to include Abseil directly in your CMake project. 4. Add the **absl::** target you wish to use to the [`target_link_libraries()`](https://cmake.org/cmake/help/latest/command/target_link_libraries.html) section of your executable or of your library.<br> Here is a short CMakeLists.txt example of an application project using Abseil. ```cmake cmake_minimum_required(VERSION 3.10) project(my_app_project) # Pick the C++ standard to compile with. # Abseil currently supports C++14, C++17, and C++20. set(CMAKE_CXX_STANDARD 14) set(CMAKE_CXX_STANDARD_REQUIRED ON) add_subdirectory(abseil-cpp) add_executable(my_exe source.cpp) target_link_libraries(my_exe absl::base absl::synchronization absl::strings) ``` Note that if you are developing a library designed for use by other clients, you should instead leave `CMAKE_CXX_STANDARD` unset (or only set if being built as the current top-level CMake project) and configure the minimum required C++ standard at the target level. If you require a later minimum C++ standard than Abseil does, it's a good idea to also enforce that `CMAKE_CXX_STANDARD` (which will control Abseil library targets) is set to at least that minimum. For example: ```cmake cmake_minimum_required(VERSION 3.10) project(my_lib_project) # Leave C++ standard up to the root application, so set it only if this is the # current top-level CMake project. if(CMAKE_SOURCE_DIR STREQUAL my_lib_project_SOURCE_DIR) set(CMAKE_CXX_STANDARD 17) set(CMAKE_CXX_STANDARD_REQUIRED ON) endif() add_subdirectory(abseil-cpp) add_library(my_lib source.cpp) target_link_libraries(my_lib absl::base absl::synchronization absl::strings) # Enforce that my_lib requires C++17. Important to document for clients that they # must set CMAKE_CXX_STANDARD to 17 or higher for proper Abseil ABI compatibility # (since otherwise, Abseil library targets could be compiled with a lower C++ # standard than my_lib). target_compile_features(my_lib PUBLIC cxx_std_17) if(CMAKE_CXX_STANDARD LESS 17) message(FATAL_ERROR "my_lib_project requires CMAKE_CXX_STANDARD >= 17 (got: ${CMAKE_CXX_STANDARD})") endif() ``` Then the top-level application project that uses your library is responsible for setting a consistent `CMAKE_CXX_STANDARD` that is sufficiently high. ### Running Abseil Tests with CMake Use the `-DABSL_BUILD_TESTING=ON` flag to run Abseil tests. Note that BUILD_TESTING must also be on (the default). You will need to provide Abseil with a Googletest dependency. There are two options for how to do this: * Use `-DABSL_USE_GOOGLETEST_HEAD`. This will automatically download the latest Googletest source into the build directory at configure time. Googletest will then be compiled directly alongside Abseil's tests. * Manually integrate Googletest with your build. See https://github.com/google/googletest/blob/master/googletest/README.md#using-cmake for more information on using Googletest in a CMake project. For example, to run just the Abseil tests, you could use this script: ``` cd path/to/abseil-cpp mkdir build cd build cmake -DABSL_BUILD_TESTING=ON -DABSL_USE_GOOGLETEST_HEAD=ON .. make -j ctest ``` Currently, we only run our tests with CMake in a Linux environment, but we are working on the rest of our supported platforms. See https://github.com/abseil/abseil-cpp/projects/1 and https://github.com/abseil/abseil-cpp/issues/109 for more information. ### Available Abseil CMake Public Targets Here's a non-exhaustive list of Abseil CMake public targets: ```cmake absl::algorithm absl::base absl::debugging absl::flat_hash_map absl::flags absl::memory absl::meta absl::numeric absl::random_random absl::strings absl::synchronization absl::time absl::utility ``` ## Traditional CMake Set-Up For larger projects, it may make sense to use the traditional CMake set-up where you build and install projects separately. First, you'd need to build and install Google Test: ``` cmake -S /source/googletest -B /build/googletest -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/installation/dir -DBUILD_GMOCK=ON cmake --build /build/googletest --target install ``` Then you need to configure and build Abseil. Make sure you enable `ABSL_USE_EXTERNAL_GOOGLETEST` and `ABSL_FIND_GOOGLETEST`. You also need to enable `ABSL_ENABLE_INSTALL` so that you can install Abseil itself. ``` cmake -S /source/abseil-cpp -B /build/abseil-cpp -DCMAKE_PREFIX_PATH=/installation/dir -DCMAKE_INSTALL_PREFIX=/installation/dir -DABSL_ENABLE_INSTALL=ON -DABSL_USE_EXTERNAL_GOOGLETEST=ON -DABSL_FIND_GOOGLETEST=ON cmake --build /temporary/build/abseil-cpp ``` (`CMAKE_PREFIX_PATH` is where you already have Google Test installed; `CMAKE_INSTALL_PREFIX` is where you want to have Abseil installed; they can be different.) Run the tests: ``` ctest --test-dir /temporary/build/abseil-cpp ``` And finally install: ``` cmake --build /temporary/build/abseil-cpp --target install ``` # CMake Option Synopsis ## Enable Standard CMake Installation `-DABSL_ENABLE_INSTALL=ON` ## Google Test Options `-DABSL_BUILD_TESTING=ON` must be set to enable testing - Have Abseil download and build Google Test for you: `-DABSL_USE_EXTERNAL_GOOGLETEST=OFF` (default) - Download and build latest Google Test: `-DABSL_USE_GOOGLETEST_HEAD=ON` - Download specific Google Test version (ZIP archive): `-DABSL_GOOGLETEST_DOWNLOAD_URL=https://.../version.zip` - Use Google Test from specific local directory: `-DABSL_LOCAL_GOOGLETEST_DIR=/path/to/googletest` - Use Google Test included elsewhere in your project: `-DABSL_USE_EXTERNAL_GOOGLETEST=ON` - Use standard CMake `find_package(CTest)` to find installed Google Test: `-DABSL_USE_EXTERNAL_GOOGLETEST=ON -DABSL_FIND_GOOGLETEST=ON`