cmake find_package

[Reprinted]

cmake find_package

cmake find_package basic principle

When compiling a software that needs to use a third -party library, we need to know where to find the header file, then cmakelist.txt needs to specify the header file directory and library file:

include_directories(/usr/include/curl)
target_link_libraries(myprogram path/curl.so)

With the help provided by Cmake. Use the FindCURL.CMAKE in the modules directory of Cmake, then cmakelists.txt:

find_package（CURL REQUIRED）
include_directories($CURL_INCLUDE_DIR)
target_link_libraries(myprogram path/curl.so)

So how do CMAKE find?

Find_package () command will first find Find.cmake in the module path, which is a typical way to find libraries. The specific search path is cmake: variable $ {cmake_module_path}. If not, then check its own module directory /Share/cmake-x.y/modules/ ($cmake_root specific values ​​can be output through the Message command in Cmake). This is called module mode.

In order to support various common libraries and packages, CMAKE has a lot of modules. The list of modules that can be supported by CMAKE -HELP-MODULE-List: View the module path directly

How to write your own cmake module module

Directory structure examples are as follows

├── cmake
│   └── FindDEMO9LIB.cmake
├── CMakeLists.txt
├── demo9.cpp
├── demo9.h
└── demo9_main.cpp

For the system pre -defined Find.cmake module, the method of use is generally as shown in the above example:
Each module defines the following variables
• _FOUND
• _INCLUDE_DIR or _INCLUDES
• _LIBRARY or _LIBRARIES

You can determine whether the module is found through _found. If it is not found, it is not found. According to the needs of the project, you can close some characteristics, give reminders or suspend compilation. The above example is to report deadly errors and terminate the construction.

system message

1, cmake_major_version, cmake main version number, such as 2 in 2.4.6
2, cmake_minor_version, cmake second version number, such as 4 in 2.4.6
3, cmake_patch_version, cmake patch level, such as 6 in 2.4.6
4, cmake_system, system name, such as Linux-2.6.22
5, cmake_system_name, does not include the system name, such as Linux
6, cmake_system_version, system version, such as 2.6.22
7, cmake_system_processor, processor name, such as i686.
8, unix, on all the UNIX platforms to True, including OS X and Cygwin
9, win32, all Win32 platforms are true, including Cygwin

Main switch options

1. Cmake_allow_loose_loop_ConStructs is used to control the writing method of if else statement, which will be mentioned in the next section of grammar.
2，BUILD_SHARED_LIBS
This switch is used to control the default library compilation method. If it is not set, the default library is static library with the default library of compiled by ADD_Library without specifying the type of library. If set (build_shared_libs on), the default is a dynamic library.
３，CMAKE_C_FLAGS
Set the C compilation option, you can also add instructions add_definitions ().
4，CMAKE_CXX_FLAGS
Set the C ++ compilation option, you can also add instructions add_definitions ().

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Some knowledge about cmake

Specifically, this is the values ​​of the project root directory (CMAKELISTS.txt at the root directory of the project, $ {Project_source_dir} indicating the corresponding path value of the Cmake/Modules subdirectory under the cmakelists.txt). Use by commands such as include () and find_package ()

• The role of the include () command:
• Including file
  • For example: include (utils.cmake)
  • Basically equivalent to #include in C/C ++
  • Need .cmake suffix
• Including modules
  • For example: Include (xxx)
  • That is to say, in the directory corresponding to the CMAKE_MODULE_PATH variable, or find xxx.cmake files in the module directory that comes with the CMAKE installation package
  • No .cmake suffix

Specifically, this is provided by the CMAKE installation packageExternalProject.cmake(For example, mine/usr/local/share/cmake/Modules/ExternalProject.cmake) The file includes in. ExternalProject, as the name suggests, introduce external engineering, all kinds of third -party libraries can be considered to use it to get it

• In other words, only in these three cases is the config mode:

• find_package()SpecifyCONFIGKeyword

• find_package()SpecifyNO_MODULEKeyword

• find_package()The keywords are not used in "Basic Signature" (that is, all supporting configurations in the Module mode)

find_package()SpecifyNO_MODULE` Keywords

• find_package()The keywords are not used in "Basic Signature" (that is, all supporting configurations in the Module mode)

In other words, as long as I do not specify "config", no "no_module", or the keyword in "Full Signature", then I am in the Module mode