9/5 cmake初步学习 Tutorial step1 and step2

cmake官方文件第一步：
https://cmake.org/cmake/help/latest/guide/tutorial/A%20Basic%20Starting%20Point.html

一个简单的开方程序用cmake来组织：
CMakeLists:

cmake_minimum_required(VERSION 3.10)

# set the project name
project(Tutorial VERSION 1.0)
set (Tutorial_VERSION_MAJOR 1)
set (Tutorial_VERSION_MINOR 0)

configure_file (
  "${PROJECT_SOURCE_DIR}/TutorialConfig.h.in"#根据.h.in生成.h文件
  "${PROJECT_BINARY_DIR}/TutorialConfig.h"
  )

include_directories("${PROJECT_BINARY_DIR}")#预处理需要的目录（要用的代码的目录）
# add the executable
add_executable(Tutorial tutorial.cpp)

TutorialConfig.h.in：

#define Tutorial_VERSION_MAJOR @Tutorial_VERSION_MAJOR@
#define Tutorial_VERSION_MINOR @Tutorial_VERSION_MINOR@

执行的指令是

mkdir build
cmake ..
cmake --build .

注意生成的TutorialConfig.h是在build下，用TutorialConfig.h.in做模板生成的。

第二步：
https://cmake.org/cmake/help/latest/guide/tutorial/Adding%20a%20Library.html
https://juejin.cn/post/6844903557196414989
把sqrt函数用自己的函数实现，并把函数打包。

CMakeLists.txt

# step2
add_library(MathFunctions mysqrt.cxx)

主CMakeLists增加:

include_directories ("${PROJECT_SOURCE_DIR}/MathFunctions")# 包含子目录的源文件
add_subdirectory (MathFunctions) # 调用子目录的CMakeLists
 
# add the executable
add_executable (Tutorial tutorial.cpp)
target_link_libraries (Tutorial MathFunctions)# 链接库文件

再增加开关,控制是否使用自己的库
TutorialConfig.h.in增加

#cmakedefine USE_MYMATH

cmakedefine 会被替换成 define，改为define也可以。

主目录下的CMakeLists修改：

cmake_minimum_required(VERSION 3.10)

# set the project name
project(Tutorial VERSION 1.0)
set (Tutorial_VERSION_MAJOR 1)
set (Tutorial_VERSION_MINOR 0)

configure_file (
  "${PROJECT_SOURCE_DIR}/TutorialConfig.h.in"
  "${PROJECT_BINARY_DIR}/TutorialConfig.h"
  )

include_directories("${PROJECT_BINARY_DIR}")
# include_directories ("${PROJECT_SOURCE_DIR}/MathFunctions")
# add_subdirectory (MathFunctions) 
 
# add the executable
# add_executable (Tutorial tutorial.cpp)
# target_link_libraries (Tutorial MathFunctions)

option (USE_MYMATH 
      "Use tutorial provided math implementation" ON)

if (USE_MYMATH)
  include_directories ("${PROJECT_SOURCE_DIR}/MathFunctions")
  add_subdirectory (MathFunctions)
  set (EXTRA_LIBS MathFunctions)# 字符串可以加引号，也可以不加
endif (USE_MYMATH)# endif要接表达式
    # add the executable
add_executable (Tutorial tutorial.cpp)
target_link_libraries (Tutorial  ${EXTRA_LIBS})

option:提供一个选项供用户选择为 ON 或 OFF。如果没有提供初始值，则使用 OFF。