4.9 KiB
Using GoogleTest from various build systems
GoogleTest comes with pkg-config files that can be used to determine all necessary flags for compiling and linking to GoogleTest (and GoogleMock). Pkg-config is a standardised plain-text format containing
- the includedir (-I) path
- necessary macro (-D) definitions
- further required flags (-pthread)
- the library (-L) path
- the library (-l) to link to
All current build systems support pkg-config in one way or another. For all
examples here we assume you want to compile the sample
samples/sample3_unittest.cc.
CMake
Using pkg-config in CMake is fairly easy:
cmake_minimum_required(VERSION 3.0)
cmake_policy(SET CMP0048 NEW)
project(my_gtest_pkgconfig VERSION 0.0.1 LANGUAGES CXX)
find_package(PkgConfig)
pkg_search_module(GTEST REQUIRED gtest_main)
add_executable(testapp samples/sample3_unittest.cc)
target_link_libraries(testapp ${GTEST_LDFLAGS})
target_compile_options(testapp PUBLIC ${GTEST_CFLAGS})
include(CTest)
add_test(first_and_only_test testapp)
It is generally recommended that you use target_compile_options + _CFLAGS
over target_include_directories + _INCLUDE_DIRS as the former includes not
just -I flags (GoogleTest might require a macro indicating to internal headers
that all libraries have been compiled with threading enabled. In addition,
GoogleTest might also require -pthread in the compiling step, and as such
splitting the pkg-config Cflags variable into include dirs and macros for
target_compile_definitions() might still miss this). The same recommendation
goes for using _LDFLAGS over the more commonplace _LIBRARIES, which happens
to discard -L flags and -pthread.
Help! pkg-config can't find GoogleTest!
Let's say you have a CMakeLists.txt along the lines of the one in this
tutorial and you try to run cmake. It is very possible that you get a failure
along the lines of:
-- Checking for one of the modules 'gtest_main'
CMake Error at /usr/share/cmake/Modules/FindPkgConfig.cmake:640 (message):
None of the required 'gtest_main' found
These failures are common if you installed GoogleTest yourself and have not
sourced it from a distro or other package manager. If so, you need to tell
pkg-config where it can find the .pc files containing the information. Say you
installed GoogleTest to /usr/local, then it might be that the .pc files are
installed under /usr/local/lib64/pkgconfig. If you set
export PKG_CONFIG_PATH=/usr/local/lib64/pkgconfig
pkg-config will also try to look in PKG_CONFIG_PATH to find gtest_main.pc.
Using pkg-config in a cross-compilation setting
Pkg-config can be used in a cross-compilation setting too. To do this, let's
assume the final prefix of the cross-compiled installation will be /usr, and
your sysroot is /home/MYUSER/sysroot. Configure and install GTest using
mkdir build && cmake -DCMAKE_INSTALL_PREFIX=/usr ..
Install into the sysroot using DESTDIR:
make -j install DESTDIR=/home/MYUSER/sysroot
Before we continue, it is recommended to always define the following two variables for pkg-config in a cross-compilation setting:
export PKG_CONFIG_ALLOW_SYSTEM_CFLAGS=yes
export PKG_CONFIG_ALLOW_SYSTEM_LIBS=yes
otherwise pkg-config will filter -I and -L flags against standard prefixes
such as /usr (see https://bugs.freedesktop.org/show_bug.cgi?id=28264#c3 for
reasons why this stripping needs to occur usually).
If you look at the generated pkg-config file, it will look something like
libdir=/usr/lib64
includedir=/usr/include
Name: gtest
Description: GoogleTest (without main() function)
Version: 1.10.0
URL: https://github.com/google/googletest
Libs: -L${libdir} -lgtest -lpthread
Cflags: -I${includedir} -DGTEST_HAS_PTHREAD=1 -lpthread
Notice that the sysroot is not included in libdir and includedir! If you try
to run pkg-config with the correct
PKG_CONFIG_LIBDIR=/home/MYUSER/sysroot/usr/lib64/pkgconfig against this .pc
file, you will get
$ pkg-config --cflags gtest
-DGTEST_HAS_PTHREAD=1 -lpthread -I/usr/include
$ pkg-config --libs gtest
-L/usr/lib64 -lgtest -lpthread
which is obviously wrong and points to the CBUILD and not CHOST root. In
order to use this in a cross-compilation setting, we need to tell pkg-config to
inject the actual sysroot into -I and -L variables. Let us now tell
pkg-config about the actual sysroot
export PKG_CONFIG_DIR=
export PKG_CONFIG_SYSROOT_DIR=/home/MYUSER/sysroot
export PKG_CONFIG_LIBDIR=${PKG_CONFIG_SYSROOT_DIR}/usr/lib64/pkgconfig
and running pkg-config again we get
$ pkg-config --cflags gtest
-DGTEST_HAS_PTHREAD=1 -lpthread -I/home/MYUSER/sysroot/usr/include
$ pkg-config --libs gtest
-L/home/MYUSER/sysroot/usr/lib64 -lgtest -lpthread
which contains the correct sysroot now. For a more comprehensive guide to also
including ${CHOST} in build system calls, see the excellent tutorial by Diego
Elio Pettenò: https://autotools.io/pkgconfig/cross-compiling.html