1## Using GoogleTest from various build systems 2 3GoogleTest comes with pkg-config files that can be used to determine all 4necessary flags for compiling and linking to GoogleTest (and GoogleMock). 5Pkg-config is a standardised plain-text format containing 6 7* the includedir (-I) path 8* necessary macro (-D) definitions 9* further required flags (-pthread) 10* the library (-L) path 11* the library (-l) to link to 12 13All current build systems support pkg-config in one way or another. For all 14examples here we assume you want to compile the sample 15`samples/sample3_unittest.cc`. 16 17### CMake 18 19Using `pkg-config` in CMake is fairly easy: 20 21```cmake 22find_package(PkgConfig) 23pkg_search_module(GTEST REQUIRED gtest_main) 24 25add_executable(testapp) 26target_sources(testapp PRIVATE samples/sample3_unittest.cc) 27target_link_libraries(testapp PRIVATE ${GTEST_LDFLAGS}) 28target_compile_options(testapp PRIVATE ${GTEST_CFLAGS}) 29 30enable_testing() 31add_test(first_and_only_test testapp) 32``` 33 34It is generally recommended that you use `target_compile_options` + `_CFLAGS` 35over `target_include_directories` + `_INCLUDE_DIRS` as the former includes not 36just -I flags (GoogleTest might require a macro indicating to internal headers 37that all libraries have been compiled with threading enabled. In addition, 38GoogleTest might also require `-pthread` in the compiling step, and as such 39splitting the pkg-config `Cflags` variable into include dirs and macros for 40`target_compile_definitions()` might still miss this). The same recommendation 41goes for using `_LDFLAGS` over the more commonplace `_LIBRARIES`, which happens 42to discard `-L` flags and `-pthread`. 43 44### Help! pkg-config can't find GoogleTest! 45 46Let's say you have a `CMakeLists.txt` along the lines of the one in this 47tutorial and you try to run `cmake`. It is very possible that you get a failure 48along the lines of: 49 50``` 51-- Checking for one of the modules 'gtest_main' 52CMake Error at /usr/share/cmake/Modules/FindPkgConfig.cmake:640 (message): 53 None of the required 'gtest_main' found 54``` 55 56These failures are common if you installed GoogleTest yourself and have not 57sourced it from a distro or other package manager. If so, you need to tell 58pkg-config where it can find the `.pc` files containing the information. Say you 59installed GoogleTest to `/usr/local`, then it might be that the `.pc` files are 60installed under `/usr/local/lib64/pkgconfig`. If you set 61 62``` 63export PKG_CONFIG_PATH=/usr/local/lib64/pkgconfig 64``` 65 66pkg-config will also try to look in `PKG_CONFIG_PATH` to find `gtest_main.pc`. 67 68### Using pkg-config in a cross-compilation setting 69 70Pkg-config can be used in a cross-compilation setting too. To do this, let's 71assume the final prefix of the cross-compiled installation will be `/usr`, and 72your sysroot is `/home/MYUSER/sysroot`. Configure and install GTest using 73 74``` 75mkdir build && cmake -DCMAKE_INSTALL_PREFIX=/usr .. 76``` 77 78Install into the sysroot using `DESTDIR`: 79 80``` 81make -j install DESTDIR=/home/MYUSER/sysroot 82``` 83 84Before we continue, it is recommended to **always** define the following two 85variables for pkg-config in a cross-compilation setting: 86 87``` 88export PKG_CONFIG_ALLOW_SYSTEM_CFLAGS=yes 89export PKG_CONFIG_ALLOW_SYSTEM_LIBS=yes 90``` 91 92otherwise `pkg-config` will filter `-I` and `-L` flags against standard prefixes 93such as `/usr` (see https://bugs.freedesktop.org/show_bug.cgi?id=28264#c3 for 94reasons why this stripping needs to occur usually). 95 96If you look at the generated pkg-config file, it will look something like 97 98``` 99libdir=/usr/lib64 100includedir=/usr/include 101 102Name: gtest 103Description: GoogleTest (without main() function) 104Version: 1.11.0 105URL: https://github.com/google/googletest 106Libs: -L${libdir} -lgtest -lpthread 107Cflags: -I${includedir} -DGTEST_HAS_PTHREAD=1 -lpthread 108``` 109 110Notice that the sysroot is not included in `libdir` and `includedir`! If you try 111to run `pkg-config` with the correct 112`PKG_CONFIG_LIBDIR=/home/MYUSER/sysroot/usr/lib64/pkgconfig` against this `.pc` 113file, you will get 114 115``` 116$ pkg-config --cflags gtest 117-DGTEST_HAS_PTHREAD=1 -lpthread -I/usr/include 118$ pkg-config --libs gtest 119-L/usr/lib64 -lgtest -lpthread 120``` 121 122which is obviously wrong and points to the `CBUILD` and not `CHOST` root. In 123order to use this in a cross-compilation setting, we need to tell pkg-config to 124inject the actual sysroot into `-I` and `-L` variables. Let us now tell 125pkg-config about the actual sysroot 126 127``` 128export PKG_CONFIG_DIR= 129export PKG_CONFIG_SYSROOT_DIR=/home/MYUSER/sysroot 130export PKG_CONFIG_LIBDIR=${PKG_CONFIG_SYSROOT_DIR}/usr/lib64/pkgconfig 131``` 132 133and running `pkg-config` again we get 134 135``` 136$ pkg-config --cflags gtest 137-DGTEST_HAS_PTHREAD=1 -lpthread -I/home/MYUSER/sysroot/usr/include 138$ pkg-config --libs gtest 139-L/home/MYUSER/sysroot/usr/lib64 -lgtest -lpthread 140``` 141 142which contains the correct sysroot now. For a more comprehensive guide to also 143including `${CHOST}` in build system calls, see the excellent tutorial by Diego 144Elio Pettenò: <https://autotools.io/pkgconfig/cross-compiling.html> 145