Find_package is a very important instruction in Cmake.Simple to use, powerful。

Let's first introduce its operation process, taking the most used opencv as an example:

1.find_packageLook for OpenCV configuration files in some directories.

2. After finding it,find_packageWill set the header file directory to${OpenCV_INCLUDE_DIRS}In, set the link library to${OpenCV_LIBS}in.

3. Set the link library and header file directory of the executable file and compile the file.

Therefore, our CMakeLists can be written like this:

add_executable(Main main.cpp)
find_package(OpenCV REQUIRED)
include_directories(${OpenCV_INCLUDE_DIRS})
target_link_libraries(Main ${OpenCV_LIBS})

After understanding the usage, the natural problem is: How does the find_package command find the Opencv configuration file?

Two modes: module mode and configuration mode. Regardless of the mode, you want to find a *.cmake file.

Module mode means: first variable${CMAKE_MODULE_PATH}Start looking in all the directories in the directory, if not, then look at its own module directory /share/cmake-x.y/Modules/ ).This is called module mode.

The configuration mode means: look up each package directory in ~/.cmake/packages/ or /usr/local/share/, look for <capitalization of the library name>Config.cmake or <lowercase of the library name>-config.cmake (For example, the library Opencv, it will look for OpenCVConfig.cmake or opencv-config.cmake in /usr/local/share/OpenCV),This is called the configuration mode.

After finding *.cmake, the following variables are generally defined in cmake:

<NAME>_FOUND
<NAME>_INCLUDE_DIRS or <NAME>_INCLUDES
<NAME>_LIBRARIES or <NAME>_LIBRARIES or <NAME>_LIBS
<NAME>_DEFINITIONS

Pay attention to the above,Especially the word or. Therefore, in CmakeLists, "include_directories(${OpenCV_INCLUDE_DIRS})" should be replaced by "include_directories(${OpenCV_INCLUDES})". When linking libraries to executables, you can also change OpenCV_LIBS to OpenCV_LIBRARIES. and many more.

Regarding this piece of content, I personally think that it is enough to understand this. If you want to further investigate the details, some friends have given a better explanation, so I do not need to repeat or copy, directly list the address:

cmake tutorial 4 (use of find_package)