Writing a custom -config.cmake module file

Let use assume you want to use the foo library, and no FindFoo.cmake for foo-config.cmake exist.

(Because it is not known enough to be in standard CMake modules, or because the foo project does not use CMake as a build system, or for whatever reason)

In any case, if you do have access to a foo-config.cmake of a FindFoo.cmake, please just use it!

Note that qi_use_lib(foo) does not need a specific foo-config.cmake to work.

It is only necessary that the foo-config.cmake code exports FOO_INCLUDE_DIRS and FOO_LIBRARIES.

Simplest case

Here we assume that the foo library only needs an include directory, and the name of the library is the same in debug and in release.

The canonical foo-config.cmake should look like

clean(FOO)
fpath(FOO foo/foo.h)
flib(FOO foo)
export_lib(FOO)

Here we assume that the library is named foo.lib for Visual Studio, libfoo.a or libfoo.so for Linux, or libfoo.a or libfoo.dylib for Mac.

We also assume that the library is in a /lib directory and the header in a include directory, and from a prefix where CMake can find it, either because:

  • foo is in a package in a toolchain following the sdk layout
  • foo is installed on the system, so the prefix is /usr/ or /usr/local.

This should cover 90% of the use cases.

If the foo library is open source, do not hesitate to submit a patch to integrate foo-config.cmake with other qibuild cmake modules.

If not, you can simply add foo-config.cmake inside your project, for instance in src/bar/cmake/modules/foo-config.cmake, and modify src/bar/CMakeLists.txt too look like:

cmake_minimum_required(VERSION 2.8)
project(bar)
find_package(qibuild)

list(APPEND CMAKE_FIND_ROOT_PATH
 ${CMAKE_SOURCE_DIR}/cmake/modules)

qi_create_bin(bar bar.cpp)
qi_use_lib(bar foo)

Finding libraries with different names

You could have to handle the case where the library is named libfoo-1.2 on linux

In this case, simply add some calls to flib

flib(FOO foo)
if (UNIX)
  flib(FOO foo-1.12)
endif()

If the foo library depends on other libraries, for instance foo-base, foo-client , foo-server, you can use

flib(FOO foo foo-base foo-client foo-server)

Note: here we assume that libfoo.so, libfoo-base.so, libfoo-client.so and libfoo-server.so are part of the same package.

If foo depends on an library from an other package (say spam), you should write a spam-config.cmake and use something like

clean(FOO)
# calling flib, fpath as usual
qi_persistent_set(FOO_DEPENDS spam)
export_lib(FOO)

Finding include directories with prefixes

Assuming foo.h is in /usr/local/include/foo/foo.h, you can use either:

fpath(FOO foo/foo.h)

In this case, FOO_INCLUDE_DIRS will equal /usr/local/include, so you will have to use

#include <foo/foo.h>

Or you can use:

fpath(FOO foo.h PATH_SUFFIXES foo)

In this case, FOO_INCLUDE_DIRS will equal usr/local/include/foo, so you will have to use

#include <foo.h>

Headers-only libraries

Some libraries are only made of headers! Let’s assume this is the case for foo.

What you have to do here is:

fpath(FOO foo/foo.h)
export_header(FOO)

In a nutshell:

  • No flib needed.
  • export_header instead of export_lib

Finding in non standards paths

Sometimes want you want to find is not under a standard location, such as /usr/local/include or /usr/include.

So, for instance let’s assume the foo library is in /opt/bar/lib/libfoo.so and the header in /opt/bar/include/foo/foo.h

All you have to do is to specify PATHS as you would do if you used the normal find_path CMake method.

So in our case

fpath(FOO foo/foo.h PATHS /opt/bar/include)
flib(FOO NAMES foo PATHS /opt/bar/lib)

Finding pkg-config libraries

If the foo library comes with a foo-1.0.pc file, you should use the PkgConfig module from CMake, like this

clean(FOO)
find_package(PkgConfig)
pkg_check_modules(FOO foo-1.0)
export_lib_pkgconfig(FOO)
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