Abseil CMake Build Instructions

Abseil comes with a CMake build script (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

If you want to build the Abseil tests, integrate the Abseil dependency Google Test 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.
Download Abseil and copy it into a subdirectory in your CMake project or add Abseil as a git submodule in your CMake project.
You can then use the CMake command add_subdirectory() to include Abseil directly in your CMake project.
Add the absl:: target you wish to use to the target_link_libraries() section of your executable or of your library.
Here is a short CMakeLists.txt example of an application project using Abseil.

cmake_minimum_required(VERSION 3.8.2)
project(my_app_project)

# Pick the C++ standard to compile with.
# Abseil currently supports C++11, C++14, and C++17.
set(CMAKE_CXX_STANDARD 11)
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_minimum_required(VERSION 3.8.2)
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:

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 Synposis

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

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