## 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
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`.



### Plain Makefiles ###

Since `pkg-config` is a small Unix command-line utility, it can be used
in handwritten `Makefile`s too:

``` Makefile
GTEST_CFLAGS = `pkg-config --cflags gtest_main`
GTEST_LIBS = `pkg-config --libs gtest_main`

.PHONY: tests all

tests: all
	./testapp

all: testapp

testapp: testapp.o
	$(CXX) $(CXXFLAGS) $(LDFLAGS) $< -o $@ $(GTEST_LIBS)

testapp.o: samples/sample3_unittest.cc
	$(CXX) $(CPPFLAGS) $(CXXFLAGS) $< -c -o $@ $(GTEST_CFLAGS)
```


### 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`.
