CMake

Tips

Sourcetrail

Create a Source Group from an existing Compilation Database file (compile_commands.json). It can be exported from CMake using -DCMAKE_EXPORT_COMPILE_COMMANDS=ON

CMake Reference/Tutorial

• Step 2: Adding a Library

• Step 3: Adding Usage Requirements for a Library

• Step 4: Installing and Testing

  • Install Rules

• Step 9: Selecting Static or Shared Libraries

• Step 10: Adding Generator Expressions

• Step 11: Adding Export Configuration

• Step 12: Packaging Debug and Release

• CMake Suggestions on Stackoverflow

1. 指定第三方库的查找路径

可以使用CMAKE_PREFIX_PATH变量指定第三方库的查找路径（指定的安装路径）

cd build
cmake -DCMAKE_PREFIX_PATH=/Users/josh/my_install_dir ..
make
# OR
cmake --install . --prefix ${PATH_TO_INSTALL}

2. 在源文件中检查某个符号是否是函数/变量/宏定义 CheckSymbolExists

在c中用
CheckSymbolExists 
在cpp中用
CheckCXXSymbolExists

3. add_subdirectory用法

直接指定要链接的子目录文件夹的相对路径即可，但是还要自己指定头文件

add_subdirectory(
  lib/sgmnv_tool
)

target_include_directories(
  ${PROJECT_NAME}
  PUBLIC
  lib/sgmnv_tool/include
)

target_link_libraries(
  ${PROJECT_NAME}
  sgmnv_tool
)

4. target_link_directories

可以配置库文件的查找目录，跟target_include_directories的效果类似

target_include_directories(
  ${PROJECT_NAME}
  PUBLIC
  src/
  src/rpc
  src/protobuf/
  src/grpcs/
  ${OpenCV_INCLUDE_DIRS}
  lib/sgmnv_tool/include
)

target_link_libraries(
  ${PROJECT_NAME}
  protobuf::libprotobuf
  gRPC::grpc++_reflection
  gRPC::grpc++
  ${OpenCV_LIBS}
  # sgmnv_tool
)

5. file命令

file命令可以使用通配符表达式方便的获取某一个文件夹下的全部源文件，例如

file(GLOB_RECURSE GRPC_SOURCES_FILE
  src/protobuf/*.cc
  src/rpc/*.cc
)

add_library(
  ${PROJECT_NAME}
  SHARED
  ${GRPC_SOURCES_FILE})

6. make打印过程中的信息

make VERBOSE=1

7. generator expression

参考链接： https://cmake.org/cmake/help/latest/manual/cmake-generator-expressions.7.html#string-valued-generator-expressions

表达式的样式 $<...>

调试方法

因为生成表达式是在编译阶段生成的，不是在执行cmake阶段生成的，所以不能用message显示，可以用下边的方法显示

add_custom_target(genexdebug COMMAND ${CMAKE_COMMAND} -E echo "$<...>")
或者
file(GENERATE OUTPUT filename CONTENT "$<...>")

8. cache

作用：缓存变量的值，在整个项目的的编译中都可以读取，一次缓存，多次编译都能读取，这个是存在build目录下CMakeCache.txt文件中的

通过set命令可以设置缓存，如果不加FORCE选项的话不会覆盖之前的值

  set(my_cache "lala" CACHE STRING "test cmake cache." FORCE)

通过unset可以删除这个缓存变量

unset(my_cache CACHE)

9. find_package()

作用：查找已经安装的包，首先在${CMAKE_MODULE_PATH}中查找，Findxxx.cmake，然后在<CMAKE_ROOT>/share/cmake-x.y/Modules/中查找Findxxx.cmake，如果这两个文件中都找不到Findxxx.cmake，则查找xxxConfig.cmake 或者xxx-config.cmake。

设置查找文件夹路径

set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_SOURCE_DIR}/cmake/Modules/")

找到后，会设置以下几个变量

xxx_FOUND
xxx_INCLUDE_DIRS or _INCLUDES
xxx_LIBRARIES or _LIBRARIES or _LIBS
xxx_DEFINITIONS

9. add_definitions

作用：在原文件中定义指定的宏，示例如下

OPTION(USE_MACRO
  "Build the project using macro"
  OFF)

if(USE_MACRO)

 add_definitions("-DUSE_MACRO")

endif(USE_MACRO)

使用时

开启：　cmake 　-DUSE_MACRO＝ON ..

关闭：　cmake 　-DUSE_MACRO＝OFF ..

10. target_compile_definitions

作用：#define xxxxx zzzz

用法：

target_compile_definitions(hello PUBLIC MY_DEFINE="nihao")

如果在编译的main.cpp中，写入如下代码的话

int main()
{
#ifdef MY_DEFINE
  cout<< MY_DEFINE << endl;
#else
  cout << "undefine" << endl;
#endif
  return 0;
}

会输出 nihao

11. 指定编译release版本或debug版本

注意：如果不使用CMAKE_BUILD_TYPE参数，则默认是Debug

-DCMAKE_BUILD_TYPE=Debug
# OR
-DCMAKE_BUILD_TYPE=Release

指定好CMAKE_BUILD_TYPE后，还要指定CMAKE_CXX_FLAGS_RELEASE或者CMAKE_CXX_FLAGS_DEBUG

# 设置Release版本的编译选项
SET(CMAKE_CXX_FLAGS_RELEASE "$ENV{CXXFLAGS} -O3 -Wall")
# 设置Debug版本的编译选项
SET(CMAKE_CXX_FLAGS_DEBUG "$ENV{CXXFLAGS} -O0 -g -Wall")

例子：

mkdir Release  
cd Release  
cmake -DCMAKE_BUILD_TYPE=Release ..  
make 

mkdir Debug  
cd Debug  
cmake -DCMAKE_BUILD_TYPE=Debug ..  
make  

12. MESSAGE

有些情况下需要指定消息的错误等级才能显示出来这个消息，用来调试用，例如

  message(FATAL_ERROR
        "The RMW implementation has been specified as "
        "'${requested_rmw_implementation}' "
        "through the environment variable 'RMW_IMPLEMENTATION', "
        "however this needs to match the RMW implementation "
        "'${default_rmw_implementation}', "
        "which was specified when the 'rmw_implementation' package was built.")

以下是全部的等级 参考链接： https://cmake.org/cmake/help/latest/command/message.html

FATAL_ERROR
CMake Error, stop processing and generation.

SEND_ERROR
CMake Error, continue processing, but skip generation.

WARNING
CMake Warning, continue processing.

AUTHOR_WARNING
CMake Warning (dev), continue processing.

DEPRECATION
CMake Deprecation Error or Warning if variable CMAKE_ERROR_DEPRECATED or CMAKE_WARN_DEPRECATED is enabled, respectively, else no message.

(none) or NOTICE
Important message printed to stderr to attract user’s attention.

STATUS
The main interesting messages that project users might be interested in. Ideally these should be concise, no more than a single line, but still informative.

VERBOSE
Detailed informational messages intended for project users. These messages should provide additional details that won’t be of interest in most cases, but which may be useful to those building the project when they want deeper insight into what’s happening.

DEBUG
Detailed informational messages intended for developers working on the project itself as opposed to users who just want to build it. These messages will not typically be of interest to other users building the project and will often be closely related to internal implementation details.

TRACE
Fine-grained messages with very low-level implementation details. Messages using this log level would normally only be temporary and would expect to be removed before releasing the project, packaging up the files, etc.

13. file命令（神器）

下边命令能将opencv的全部库文件都添加到link中

file(GLOB_RECURSE dyso "/Users/liushichao/Exercise/build_opencv_4.3.0/lib/*.dylib")
target_link_libraries(test_sort
${dyso}
)
MESSAGE("${dyso}")

14. if语句

执行cmake -DUSER_DEFINE=dadah ./，返回”err”.

if(NOT "${USER_DEFINE}" STREQUAL "dadah")
  MESSAGE("ok.")
else()
  MESSAGE("err.")
endif()

15. get_filename_component

获取第二个参数的绝对路径，存到第一个参数重，执行完后 ANDROID_NDK_EXPECTED_PATH 中存储的事当前路径的绝对路径

get_filename_component(ANDROID_NDK_EXPECTED_PATH
    "./" ABSOLUTE)

16. 使用环境变量

$ENV{xxx}可以获取环境变量xxx

MESSAGE("$ENV{PATH}")

17. cmake路径

为了统一路径中的分割符windows c:\xx linux /usr/xxx，cmake定义了统一的分割符/的路径表示方式，可以用file命令进行转换

file(TO_CMAKE_PATH "<path>" <variable>)
file(TO_NATIVE_PATH "<path>" <variable>)

18. 指定c++标准库版本

cmake_minimum_required(VERSION 3.10)

# set the project name and version
project(Tutorial VERSION 1.0)

# specify the C++ standard
set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED True)

19. include命令

通过定义xxx.cmake，可以重用cmake的代码 可以指定包含的文件的全路径，或者让cmake去搜索，搜索顺序：1. CMAKE_MODULE_PATH变量指定的路径 2. cmake自己的Modules文件夹/usr/local/Cellar/cmake/3.18.1/share/cmake/Modules

include(xxx.cmake)

20. find_path()

在/Users/liushichao/workspace下创建1.txt,执行下边代码，返回/Users/josh/workspace。 如果没有找到，返回TXT_PATH-NOTFOUND 这个TXT_PATH如果被设置后，以后不会被更新

find_path(TXT_PATH "1.txt" /Users/josh/workspace/123 /Users/josh/workspace)
MESSAGE("${TXT_PATH}")

21. configure_file

将输入文件，转换成输出文件，可以自定义变量，改变输出文件中的值 例如在cmakelist文件夹下定义一个foo.h.in文件，或者在其他目录里创建，然后cmakelist.txt文件中指明相对路径 在foo.h.in中可以加入如下定义

//foo.h.in

#cmakedefine XXXX "@XXXX@"
@bbb@

编辑CMakeLists.txt

//CMakeLists.txt

set(bbb "nihao")
set(XXXX "hahah")
configure_file(foo.h.in foo.h @ONLY)

会在执行cmake命令的目录里生成foo.h文件，内容如下

//foo.h

#define XXXX "hahah"
nihao

如果CMakeLists.txt文件中没有写set(bbb “nihao”) 也没写 set(XXXX “hahah”)，则生成的文件如下

//foo.h

/* #undef XXXX */

22. cmake的function

定义如下，第一个参数是函数名，第二个参数是传入的参数

function(func_name list)
  MESSAGE("${list}") #abc
  MESSAGE("${${list}}") #a;b;c
endfunction()

调用方法如下

set(abc a b c)
func_name(abc)

输出

abc
a;b;c