CMake from entry to entry

I. Overview

1, CMake role

CMake is a cross-platform, open-source build system. It is a set of software building, testing, packing and one software. For example, you can build a profile build of Visual Studio .sln files in the Makefile or Linux based on the source code and pre-configured, start the compilation process start unit testing, packaging, executable files and depend to a specified directory.

2, CMake advantage

1. Cross-platform support for Windows, Linux, Mac, Android system;
2. Scalability, and support for control logic syntax, conditional compilation;

Two, CMake example of Helloworld

CMake build process configuration items by CMakeLists.txt file, which is usually located in the root directory of the project. Other file formats as well xxx.cmake, similar to the function of such files in the C ++ header file, may be include into the CMakeLists.txt to scale the configuration of the build.

1, the project directory, configuration CMakeLists.txt

• Create a src directory that contains hello.cpp file;
• The root directory is created CMakeLists.txt;
• build directory is an empty directory, the process of building (construction process will produce some profiles, in order to prevent contamination source, constructed in a separate folder);

The figure CMakeLists.txt document explains:

• project(hello) Configuring project called hello;
• add_executable(hello src/hello.cpp)Configured to generate an executable file, the executable file is named hello, a file link is involved src/hello.cpp;

2. Build Solution

By using cmake command, specify the root directory CMakeLists.txt position to generate project solutions.

Above will generate a Visual Studio solution hello.slnengineering and hello project configuration hello.vcxproj.

3, building

Previous simply generate a solution, we want hello.exedoes not get created. Can be opened with a graphical interface hello.vcprojgeneration may be generated directly from the command line.

In the build directory execute cmake --build .:

Three, CMake common keywords

1, project management

(1) include_directory

Configuration header file path, can be configured with multiple paths simultaneously. such as:include_directory(CMAKE_SOURCE_DIR/include1 CMAKE_CURRENT_SOURCE_DIR/../include2)

The above contains two variables CMAKE_SOURCE_DIR, CMAKE_CURRENT_SOURCE_DIR:

• CMAKE_SOURCE_DIR: CMakeLists.txt the beginning of the path, such as using the cmake ..build, referring to the CMakeLists.txt path under the project root directory;
• CMAKE_CURRENT_SOURCE_DIR: Current CMakeLists.txt the path (there may be a plurality of CMakeLists.txt);

(2) add_executable、add_library

How the former configured to generate an executable file, which is how to generate the configuration database file. Such as:

add_executable(可执行文件名 源码列表)
add_library(动态链接库名称 SHARED 源码列表)
add_library(静态链接库名称 STATIC 源码列表)
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In the implementation of the link, usually specify additional libraries. CMake by library_directorythe specified link library path, through the target_link_librariesdesignated link library name, equivalent to the Makefileinside -Land -las:

library_directory(CMAKE_BINARY_DIR/lib)    # CMAKE_BINARY_DIR是执行cmake命令的目录
target_link_libraries(二进制文件名 链接库名列表)
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(3) add_subdirectory、include

For the above helloworldsimple to use, you might think to write Makefilesimpler, but if the entire solution like this, you would write Makefileit?

A single solution project is too big, CMake using divide and conquer to solve. CMake by using a single configuration file for each module, at the root of the introduction of these profiles.

• add_subdirectoryThe argument is a module directory. CMake will find in the catalog CMakeLists.txtfile, and perform inside the configuration script;
• includeThe argument is a file name, usually similar xxx.cmakedocuments;

2, switch options

By performing CMake cmake命令when -Doption, a control switch of a compiler option. For example, the following CMakeLists.txt:

project(hello)
option("ENABLE_FEATURE", "whether enable some feature", OFF)    # 定义一个开关，是否开启某一个指定功能，默认关闭

if(ENABLE_FEATURE)
add_executable(hello src/hello.cpp feature.cpp)    # 假设特定功能就是多链接一个文件
else
add_executable(hello src/hello.cpp)
endif
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Use when building cmake .. -DENABLE_FEATURE=ONopen specified function, if there is no -Doption or to ONchange OFF, then closes the specified function.

option defined options can only be used in CMakeLists.txt , 如果想在源码中识别是否定义了某一个开关呢? add_definition can perform this function. such as:

if(ENABLE_FEATURE)
add_definition(FEATURE)    # 如果ENABLE_FEATURE开启，则定义FEATURE宏
elsec
endif
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By increasing macro definitions in the source code of the macro is determined to achieve the same switching function.

3, debugging information

(1) message

Print information. Format:message(<mode> "debug info: value of arg: ${arg}") . message function has at least the following modes (MODE):STATUS , , , . Which mode stops the build in failure and quit.INFOWARNINGFATAL_ERRORFATAL_ERROR

4, other variables CMake

(1) CMAKE_C_FLAGS、CMAKE_CXX_FLAGS

Resolution control C / C ++ compiler options. For example: set(CMAKE_CXX_FLAGS "std-c++11 ${CMAKE_CXX_FLAGS}")# extension CMAKE_CXX_FLAGSvalue, adding support for C ++ 11's.

(2) CMAKE_BUILD_TYPE

Specify the type of building, passing by when building using cmake command. such as:cmake .. -DCMAKE_BUILD_TYPE=Release