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Using CMake with pkg-config ​

One of the difficulties with using C/C++ is related to the integration of various libraries and dependencies needed for an application. pkg-config is a metadata system that helps ease this process by providing information about how to integrate libraries into a program. While there are a number of ways to use pkg-config and cmake, here I outline a few specific methods that have worked well for me in the past.

Creating a Library that has pkg-config ​

Say your project is called foo, such that your top-level CMakeLists.txt contains the block

cmake
project(foo
    VERSION 0.1.6
    DESCRIPTION "Foo C++ library"
)
project(foo
    VERSION 0.1.6
    DESCRIPTION "Foo C++ library"
)

In your project, create a pkg-config.in file with the following contents.

prefix=@CMAKE_INSTALL_PREFIX@
exec_prefix="${prefix}"
libdir="${prefix}"/lib
includedir="${prefix}"/include

Name: lib@CMAKE_PROJECT_NAME@
Version: @CMAKE_PROJECT_VERSION@
Description: @CMAKE_PROJECT_DESCRIPTION@
Libs: -L${libdir} -lfoo
Libs.private: -ldep1 -ldep2
Cflags: -I${includedir}/libfoo
prefix=@CMAKE_INSTALL_PREFIX@
exec_prefix="${prefix}"
libdir="${prefix}"/lib
includedir="${prefix}"/include

Name: lib@CMAKE_PROJECT_NAME@
Version: @CMAKE_PROJECT_VERSION@
Description: @CMAKE_PROJECT_DESCRIPTION@
Libs: -L${libdir} -lfoo
Libs.private: -ldep1 -ldep2
Cflags: -I${includedir}/libfoo

The Libs.private field is used to identify any dependencies of the library itself, while the Libs field identifies the install location of the library (-L) and the library name (-l), respectively. See this thread for another explanation of -L and -l. Note, the variables nested between @ symbols will be replaced once the project is built.

Next, in the top-level CMakeLists.txt, add the following lines

cmake
configure_file(pc.in lib${CMAKE_PROJECT_NAME}.pc @ONLY)
install(
    FILES ${PROJECT_BINARY_DIR}/lib${CMAKE_PROJECT_NAME}.pc
    DESTINATION "local/lib/pkgconfig"
)
configure_file(pc.in lib${CMAKE_PROJECT_NAME}.pc @ONLY)
install(
    FILES ${PROJECT_BINARY_DIR}/lib${CMAKE_PROJECT_NAME}.pc
    DESTINATION "local/lib/pkgconfig"
)

When the project is built with something like cpack, this will create a file at /usr/local/lib/pkgconfig/libfoo.pc.

Using a Library in a Program ​

Say you're writing a program that uses ZeroMQ. Depending on your system, the ZeroMQ pkg-config file may be located at /usr/lib/x86_64-linux-gnu/pkgconfig/libzmq.pc.

This file contains the following information.

prefix=/usr
exec_prefix=${prefix}
libdir=${prefix}/lib/x86_64-linux-gnu
includedir=${prefix}/include

Name: libzmq
Description: 0MQ c++ library
Version: 4.3.2
Libs: -L${libdir} -lzmq
Libs.private: -lstdc++  -lpthread -lrt
Requires.private:  krb5-gssapi libsodium openpgm-5.2 >= 5.2 norm
Cflags: -I${includedir}
prefix=/usr
exec_prefix=${prefix}
libdir=${prefix}/lib/x86_64-linux-gnu
includedir=${prefix}/include

Name: libzmq
Description: 0MQ c++ library
Version: 4.3.2
Libs: -L${libdir} -lzmq
Libs.private: -lstdc++  -lpthread -lrt
Requires.private:  krb5-gssapi libsodium openpgm-5.2 >= 5.2 norm
Cflags: -I${includedir}

To use ZeroMQ with *pkg-config, in your top-level *CMakeLists.txt* add the following block.

cmake
find_package(PkgConfig REQUIRED)
pkg_search_module(LIBZMQ REQUIRED IMPORTED_TARGET libzmq)
find_package(PkgConfig REQUIRED)
pkg_search_module(LIBZMQ REQUIRED IMPORTED_TARGET libzmq)

Then, add the include directory and link library to your executable target.

cmake
target_include_directories(${CMAKE_PROJECT_NAME}
  PRIVATE
    ${LIBZMQ_INCLUDE_DIRS}
)

target_link_libraries(${CMAKE_PROJECT_NAME}
  PUBLIC
    PkgConfig::LIBZMQ
)
target_include_directories(${CMAKE_PROJECT_NAME}
  PRIVATE
    ${LIBZMQ_INCLUDE_DIRS}
)

target_link_libraries(${CMAKE_PROJECT_NAME}
  PUBLIC
    PkgConfig::LIBZMQ
)
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