I have written a library that I used to compile using a self-written Makefile, but now I want to switch to cmake. The tree looks like this (I removed all the irrelevant files):
.
├── include
│ ├── animation.h
│ ├── buffers.h
│ ├── ...
│ ├── vertex.h
│ └── world.h
└── src
├── animation.cpp
├── buffers.cpp
├── ...
├── vertex.cpp
└── world.cpp
So what I am trying to do is just to compile the source into a shared library and then install it with the header files.
Most examples that I have found compile executables with some shared libraries but never just a plain shared library. It would also be helpful if someone could just tell me a very simple library that uses cmake, so I can use this as an example.
Always specify the minimum required version of cmake
cmake_minimum_required(VERSION 3.9)
You should declare a project. cmake
says it is mandatory and it will define convenient variables PROJECT_NAME
, PROJECT_VERSION
and PROJECT_DESCRIPTION
(this latter variable necessitate cmake 3.9):
project(mylib VERSION 1.0.1 DESCRIPTION "mylib description")
Declare a new library target. Please avoid the use of file(GLOB ...)
. This feature does not provide attended mastery of the compilation process. If you are lazy, copy-paste output of ls -1 sources/*.cpp
:
add_library(mylib SHARED
sources/animation.cpp
sources/buffers.cpp
[...]
)
Set VERSION
property (optional but it is a good practice):
set_target_properties(mylib PROPERTIES VERSION ${PROJECT_VERSION})
You can also set SOVERSION
to a major number of VERSION
. So libmylib.so.1
will be a symlink to libmylib.so.1.0.0
.
set_target_properties(mylib PROPERTIES SOVERSION 1)
Declare public API of your library. This API will be installed for the third-party application. It is a good practice to isolate it in your project tree (like placing it include/
directory). Notice that, private headers should not be installed and I strongly suggest to place them with the source files.
set_target_properties(mylib PROPERTIES PUBLIC_HEADER include/mylib.h)
If you work with subdirectories, it is not very convenient to include relative paths like "../include/mylib.h"
. So, pass a top directory in included directories:
target_include_directories(mylib PRIVATE .)
or
target_include_directories(mylib PRIVATE include)
target_include_directories(mylib PRIVATE src)
Create an install rule for your library. I suggest to use variables CMAKE_INSTALL_*DIR
defined in GNUInstallDirs
:
include(GNUInstallDirs)
And declare files to install:
install(TARGETS mylib
LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
PUBLIC_HEADER DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
You may also export a pkg-config
file. This file allows a third-party application to easily import your library:
pkg-config
PKG_CHECK_MODULES
pkg_check_modules
Create a template file named mylib.pc.in
(see pc(5) manpage for more information):
prefix=@CMAKE_INSTALL_PREFIX@
exec_prefix=@CMAKE_INSTALL_PREFIX@
libdir=${exec_prefix}/@CMAKE_INSTALL_LIBDIR@
includedir=${prefix}/@CMAKE_INSTALL_INCLUDEDIR@
Name: @PROJECT_NAME@
Description: @PROJECT_DESCRIPTION@
Version: @PROJECT_VERSION@
Requires:
Libs: -L${libdir} -lmylib
Cflags: -I${includedir}
In your CMakeLists.txt
, add a rule to expand @
macros (@ONLY
ask to cmake to not expand variables of the form ${VAR}
):
configure_file(mylib.pc.in mylib.pc @ONLY)
And finally, install generated file:
install(FILES ${CMAKE_BINARY_DIR}/mylib.pc DESTINATION ${CMAKE_INSTALL_DATAROOTDIR}/pkgconfig)
You may also use cmake EXPORT
feature. However, this feature is only compatible with cmake
and I find it difficult to use.
Finally the entire CMakeLists.txt
should looks like:
cmake_minimum_required(VERSION 3.9)
project(mylib VERSION 1.0.1 DESCRIPTION "mylib description")
include(GNUInstallDirs)
add_library(mylib SHARED src/mylib.c)
set_target_properties(mylib PROPERTIES
VERSION ${PROJECT_VERSION}
SOVERSION 1
PUBLIC_HEADER api/mylib.h)
configure_file(mylib.pc.in mylib.pc @ONLY)
target_include_directories(mylib PRIVATE .)
install(TARGETS mylib
LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
PUBLIC_HEADER DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
install(FILES ${CMAKE_BINARY_DIR}/mylib.pc
DESTINATION ${CMAKE_INSTALL_DATAROOTDIR}/pkgconfig)