CMake¶

cmake不同工程类型的样例，所有样例可在GitHub仓库中找到

Exec工程¶

cmake通过目录下的CMakeLists.txt文件，将整个工程串联起来。在主目录的CMakeLists.txt文件中，通过add_subdirectory命令加入子一级的目录，以此类推。

主配置文件 ¶

主配置文件主要配置一些全局信息。例如，项目名称，C++库版本等。同时加入子一级目录。

cmake_minimum_required(VERSION 3.13)

# Setting a project name
project(exec VERSION 1.0
DESCRIPTION "EXEC Project"
LANGUAGES CXX)

# set the C++ standard
set(CMAKE_CXX_STANDARD 20)
# Use STD c++ instead of GNU
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)

message(STATUS "[ROOT] CMAKE_BINARY_DIR ${CMAKE_BINARY_DIR}")
message(STATUS "[ROOT] CMAKE_SOURCE_DIR ${CMAKE_SOURCE_DIR}")
message(STATUS "[ROOT] CMAKE_CXX_COMPILER ${CMAKE_CXX_COMPILER}")

######################
# Add Targets
######################
add_subdirectory(src)

Exec目标配置文件 ¶

为了统一，可选择set_target_properties命令，为此目标配置所有的编译信息

编译和链接选项通过分号隔离

默认文件输出路径就是CMAKE_CURRENT_BINARY_DIR

set_target_properties(EXEC PROPERTIES
    COMPILE_OPTIONS "-Wall;-Werror;-Wpedantic;-I."
    LINK_OPTIONS "-Wl,-Map=output.map,--print-memory-usage;-L."
    RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
)

如果不想用分号隔离编译和链接选项，可以通过separate_arguments命令将空格转换成分号，从而选项的写法就不会那么奇怪，下面的写法和上面的的写法是相同的，但是可读性更好也更不容易出错：

separate_arguments(COMPILE_OPTION UNIX_COMMAND "-Wall -Werror -Wpedantic -I.")
separate_arguments(LINK_OPTION UNIX_COMMAND "-Wl,-Map=output.map,--print-memory-usage -L.")
set_target_properties(EXEC PROPERTIES
    COMPILE_OPTIONS "${COMPILE_OPTION}"
    LINK_OPTIONS "${LINK_OPTION}"
    RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
)

开启verbose后，可得到完整的编译链接命令

编译命令

[ 50%] Building CXX object src/CMakeFiles/EXEC.dir/main.cpp.o
cd /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/exec/build/src && /usr/bin/c++   -g -Wall -Werror -Wpedantic -I. -std=c++20 -MD -MT src/CMakeFiles/EXEC.dir/main.cpp.o -MF CMakeFiles/EXEC.dir/main.cpp.o.d -o CMakeFiles/EXEC.dir/main.cpp.o -c /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/exec/src/main.cpp

链接命令

[100%] Linking CXX executable EXEC
cd /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/exec/build/src && /usr/bin/cmake -E cmake_link_script CMakeFiles/EXEC.dir/link.txt --verbose=1
/usr/bin/c++ -g -Wl,-Map=output.map,--print-memory-usage -L. CMakeFiles/EXEC.dir/main.cpp.o -o EXEC 
Memory region         Used Size  Region Size  %age Used

cmake目标¶

cmake配置完成后，可通过cmake生成对应的Makefile。此工程的目标有：

build> make help
The following are some of the valid targets for this Makefile:
... all (the default if no target is provided)
... clean
... depend
... edit_cache
... rebuild_cache
... EXEC

其中，EXEC是我们定义的目标，其他的是由cmake自己生成的。

动态库工程¶

动态库通过add_library命令添加目标，而EXEC工程通过add_executable添加工程。除了这个区别，其他配置两者基本一致。

动态库配置文件 ¶

为了方便查找动态库的头文件，通过target_include_directories命令，将目录文件输出

file(GLOB_RECURSE SRC_CPP ${CMAKE_CURRENT_SOURCE_DIR} "*.cpp")
# Set SHARED to build so library
add_library(mylib SHARED ${SRC_CPP})
# Set public so that its dependency can get the include directory
target_include_directories(mylib PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})

编译命令

先编译.o文件

再将所有.o文件链接成.so文件

[ 25%] Building CXX object src/CMakeFiles/mylib.dir/hello.cpp.o
cd /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/libso/build/src && /usr/bin/c++ -Dmylib_EXPORTS -I/home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/libso/src -g -fPIC -std=c++20 -MD -MT src/CMakeFiles/mylib.dir/hello.cpp.o -MF CMakeFiles/mylib.dir/hello.cpp.o.d -o CMakeFiles/mylib.dir/hello.cpp.o -c /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/libso/src/hello.cpp
[ 50%] Linking CXX shared library libmylib.so
cd /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/libso/build/src && /usr/bin/cmake -E cmake_link_script CMakeFiles/mylib.dir/link.txt --verbose=1
/usr/bin/c++ -fPIC -g -shared -Wl,-soname,libmylib.so -o libmylib.so CMakeFiles/mylib.dir/hello.cpp.o 
make[3]: Leaving directory '/home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/libso/build'

动态库测试配置文件 ¶

通过target_link_libraries命令就可以链接到动态库，由于动态库工程已经将其头文件目录PUBLIC输出，所以此处能找到头文件
```
target_link_libraries(myTest PRIVATE
    mylib
)
```

编译命令

[ 75%] Building CXX object test/CMakeFiles/myTest.dir/main.cpp.o
cd /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/libso/build/test && /usr/bin/c++  -I/home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/libso/src -g -std=c++20 -MD -MT test/CMakeFiles/myTest.dir/main.cpp.o -MF CMakeFiles/myTest.dir/main.cpp.o.d -o CMakeFiles/myTest.dir/main.cpp.o -c /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/libso/test/main.cpp
[100%] Linking CXX executable myTest
cd /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/libso/build/test && /usr/bin/cmake -E cmake_link_script CMakeFiles/myTest.dir/link.txt --verbose=1
/usr/bin/c++ -g CMakeFiles/myTest.dir/main.cpp.o -o myTest  -Wl,-rpath,/home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/libso/build/src ../src/libmylib.so 
make[3]: Leaving directory '/home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/libso/build'

静态库工程¶

静态库工程和动态工程除了在add_library命令中使用STATIC选项以外，其他和动态库工程完全一样。

静态库配置文件 ¶

通过add_library(mylib STATIC ${SRC_CPP})配置了静态库目标

编译命令

[ 25%] Building CXX object src/CMakeFiles/mylib.dir/hello.cpp.o
cd /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/liba/build/src && /usr/bin/c++  -I/home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/liba/src -g -std=c++20 -MD -MT src/CMakeFiles/mylib.dir/hello.cpp.o -MF CMakeFiles/mylib.dir/hello.cpp.o.d -o CMakeFiles/mylib.dir/hello.cpp.o -c /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/liba/src/hello.cpp
[ 50%] Linking CXX static library libmylib.a
cd /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/liba/build/src && /usr/bin/cmake -P CMakeFiles/mylib.dir/cmake_clean_target.cmake
cd /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/liba/build/src && /usr/bin/cmake -E cmake_link_script CMakeFiles/mylib.dir/link.txt --verbose=1
/usr/bin/ar qc libmylib.a CMakeFiles/mylib.dir/hello.cpp.o
/usr/bin/ranlib libmylib.a
make[3]: Leaving directory '/home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/liba/build'

源代码导入工程¶

将其他目录下的源代码和当前目录的源代码一起编译，可以排除因编译器版本不同，而造成目标文件的兼容问题。cmake提供了： * aux_source_directory(<dir> <variable>) * 用于将指定目录下所有的源文件记录在<varible>中，以便和当前目录的源文件同时编译

导入源代码配置文件 ¶

先通过aux_source_directory(${CMAKE_CURRENT_SOURCE_DIR}/src1 SRCS1)命令，将src1目录下的所有源代码文件记录在SRCS1变量中
再通过add_executable(SRC_IMPORT_EXEC ${SRCS1} ${SRCS2} main.cpp)命令，将其他目录下的源代码和当前目录下的源代码一起编译

自定义工程¶

除了常规目标(EXEC，静态库，动态库)，cmake还提供了一些命令用于用户自定义的目标：

add_custom_command
- 用于产生当前目标的依赖文件，本文的例子就用此命令执行了自动生成的代码，用于当前目标的编译
add_custom_target
- 创建一个非常规的目标。例如，我们可以用其创建一个doxygen目标用来生成代码文档
add_dependencies
- 建立自定义依赖关系。cmake对库依赖会自动建立依赖关系，但是如果我们想建立一个非常规的依赖关系，就需要用到此命令。例如，建立自定义目标的依赖关系
- 当依赖关系建立好后，系统会按照依赖关系进行按顺序编译

自定义目标配置文件 ¶

本例的编译顺序如下，可参考简单的Makefile文件：

先通过python的cog命令自动生成CPP源代码
再将main.cpp与生成的代码进行编译
最终生成一个可执行文件

自定义目标的配置文件如下：

set(CODEGEN_BINARY_DIR "${CMAKE_CURRENT_BINARY_DIR}/internal")
set(CODEGEN_SRC "${CODEGEN_BINARY_DIR}/animal.cpp")

add_executable(main main.cpp ${CODEGEN_SRC})

add_custom_command(
   OUTPUT ${CODEGEN_SRC}
   # Copy all files in this folder to $(CODEGEN_BINARY_DIR)
   COMMAND ${CMAKE_COMMAND} -E copy_directory
        ${CMAKE_CURRENT_SOURCE_DIR}/internal ${CODEGEN_BINARY_DIR}
   COMMAND make -C ${CODEGEN_BINARY_DIR}
   COMMENT "Generate C++ code with cog python tool"
   VERBATIM
)

set_target_properties(main PROPERTIES
   COMPILE_OPTIONS "-I${CODEGEN_BINARY_DIR}"
   LINK_OPTIONS ""
   RUNTIME_OUTPUT_DIRECTORY ""
)

internal文件夹用于代码生成，在执行前被拷贝到目标工作目录CMAKE_CURRENT_BINARY_DIR下
由于当前目标依赖生成的源文件，所以在编译的时候要加入头文件目录，以防止自动生成了依赖的头文件在编译时无法找到

编译命令

源文件自动生成命令

[ 25%] Generate C++ code with cog python tool
cd /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/custom/build/src && /usr/bin/cmake -E copy_directory /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/custom/src/internal /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/custom/build/src/internal
cd /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/custom/build/src && make -C /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/custom/build/src/internal
make[4]: Entering directory '/home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/custom/build/src/internal'
python3 -m cogapp -d -s " //cog generated" -o animal.cpp animal.cpp.cog
make[4]: Leaving directory '/home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/custom/build/src/internal'

编译链接命令

[ 50%] Building CXX object src/CMakeFiles/main.dir/main.cpp.o
cd /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/custom/build/src && /usr/bin/c++   -g -I/home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/custom/build/src/internal -std=c++20 -MD -MT src/CMakeFiles/main.dir/main.cpp.o -MF CMakeFiles/main.dir/main.cpp.o.d -o CMakeFiles/main.dir/main.cpp.o -c /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/custom/src/main.cpp
[ 75%] Building CXX object src/CMakeFiles/main.dir/internal/animal.cpp.o
cd /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/custom/build/src && /usr/bin/c++   -g -I/home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/custom/build/src/internal -std=c++20 -MD -MT src/CMakeFiles/main.dir/internal/animal.cpp.o -MF CMakeFiles/main.dir/internal/animal.cpp.o.d -o CMakeFiles/main.dir/internal/animal.cpp.o -c /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/custom/build/src/internal/animal.cpp
[100%] Linking CXX executable main
cd /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/custom/build/src && /usr/bin/cmake -E cmake_link_script CMakeFiles/main.dir/link.txt --verbose=1
/usr/bin/c++ -g CMakeFiles/main.dir/main.cpp.o CMakeFiles/main.dir/internal/animal.cpp.o -o main 
make[3]: Leaving directory '/home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/custom/build'

WebAssembly工程¶

另一篇文章“WebAssembly”介绍了WebAssembly和C/C++的用法。当时的例子是用Makefile集成编译的。通过emcmake结合cmake命令可以方便地将C/C++ cmake工程编译成“WebAssembly”工程，命令如下：

web: clean
    emcmake cmake -S . -B build
    cmake --build ./build --verbose

修改静态库工程¶

通过将静态库工程的cmake配置命令变成emcmake cmake，就可直接编译成“WebAssembly”工程，可参考其Makefile中的web目标。

编译命令

静态库

[ 25%] Building CXX object src/CMakeFiles/mylib.dir/hello.cpp.o
cd /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/liba/build/src && /home/yuxiangw/emsdk/upstream/emscripten/em++  @CMakeFiles/mylib.dir/includes_CXX.rsp -std=c++20 -MD -MT src/CMakeFiles/mylib.dir/hello.cpp.o -MF CMakeFiles/mylib.dir/hello.cpp.o.d -o CMakeFiles/mylib.dir/hello.cpp.o -c /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/liba/src/hello.cpp
[ 50%] Linking CXX static library libmylib.a
cd /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/liba/build/src && /usr/bin/cmake -P CMakeFiles/mylib.dir/cmake_clean_target.cmake
cd /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/liba/build/src && /usr/bin/cmake -E cmake_link_script CMakeFiles/mylib.dir/link.txt --verbose=1
/home/yuxiangw/emsdk/upstream/emscripten/emar qc libmylib.a CMakeFiles/mylib.dir/hello.cpp.o
/home/yuxiangw/emsdk/upstream/emscripten/emranlib libmylib.a
make[3]: Leaving directory '/home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/liba/build'

链接命令存在于CMakeFiles/mylib.dir/link.txt文件，通过emar命令进行压缩

/home/yuxiangw/emsdk/upstream/emscripten/emar qc libmylib.a CMakeFiles/mylib.dir/hello.cpp.o
/home/yuxiangw/emsdk/upstream/emscripten/emranlib libmylib.a

WASM和JS文件

[ 75%] Building CXX object test/CMakeFiles/myTest.dir/main.cpp.o
cd /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/liba/build/test && /home/yuxiangw/emsdk/upstream/emscripten/em++  @CMakeFiles/myTest.dir/includes_CXX.rsp -std=c++20 -MD -MT test/CMakeFiles/myTest.dir/main.cpp.o -MF CMakeFiles/myTest.dir/main.cpp.o.d -o CMakeFiles/myTest.dir/main.cpp.o -c /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/liba/test/main.cpp
[100%] Linking CXX executable myTest.js
cd /home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/liba/build/test && /usr/bin/cmake -E cmake_link_script CMakeFiles/myTest.dir/link.txt --verbose=1
/home/yuxiangw/emsdk/upstream/emscripten/em++ @CMakeFiles/myTest.dir/objects1.rsp -o myTest.js @CMakeFiles/myTest.dir/linklibs.rsp
make[3]: Leaving directory '/home/yuxiangw/GitHub/learning_book/docs/topics/cmake/code/liba/build'

同样，链接命令也存在与CMakeFiles/myTest.dir/link.txt文件中

CMake¶

Exec工程¶

主配置文件¶

Exec目标配置文件¶

cmake目标¶

动态库工程¶

动态库配置文件¶

动态库测试配置文件¶

静态库工程¶

静态库配置文件¶

源代码导入工程¶

导入源代码配置文件¶

自定义工程¶

自定义目标配置文件¶

WebAssembly工程¶

修改静态库工程¶

参考¶

主配置文件 ¶

Exec目标配置文件 ¶

动态库配置文件 ¶

动态库测试配置文件 ¶

静态库配置文件 ¶

导入源代码配置文件 ¶

自定义目标配置文件 ¶