1. 添加文件夹与文件

在CMake_Tutorial文件夹中添加子目录MathFunctions，并在该目录中添加以下三个文件：

CMakeLists.txt
MathFunctions.h
mysqrt.cpp
文件内容分别如下：

1.1 CMakeLists.txt

add_library(MathFunctions mysqrt.cpp)

1.2 MathFunctions.h

double mysqrt(double x);

1.3 mysqrt.cpp

#include <iostream>
#include "MathFunctions.h"

// a hack square root calculation using simple operations
double mysqrt(double x)
{
  if (x <= 0)
  {
    return 0;
  }

  double result = x;

  // do ten iterations
  for (int i = 0; i < 10; ++i)
  {
    if (result <= 0)
    {
      result = 0.1;
    }
    double delta = x - (result * result);
    result = result + 0.5 * delta / result;
    std::cout << "Computing sqrt of " << x << " to be " << result << std::endl;
  }
  return result;
}

2. 修改顶层目录中的CMakeLists.txt

cmake_minimum_required(VERSION 3.20 FATAL_ERROR)
project(Tutorials)

# 指定C++版本
set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED True)

# 设置版本号
set(Tutorial_VERSION_MAJOR 1)
set(Tutorial_VERSION_MINOR 0)

# 添加配置文件，编译后 TutorialConfig.h.in 将被转化成 TutorialConfig.h 文件，该文件位于项目文件的根目录
configure_file(TutorialConfig.h.in TutorialConfig.h)

# 添加一个名称为 MathFunctions 的库
add_subdirectory(MathFunctions)

add_executable(Tutorial main.cpp)
# 包含特定的头文件查找目录，以便于找到TutorialConfig.h文件
target_include_directories(Tutorial PUBLIC 
                           ${PROJECT_BINARY_DIR}
                           ${PROJECT_SOURCE_DIR}/MathFunctions)
# 添加链接库文件
target_link_libraries(Tutorial PUBLIC MathFunctions)

3. 修改main.cpp文件

#include <iostream>
#include "TutorialConfig.h"
#include "MathFunctions.h"

int main(int argc, char** argv)
{
    std::cout << "Hello World!" << std::endl;
    // 版本信息
    std::cout << " Version: " << Tutorial_VERSION_MAJOR << "." << Tutorial_VERSION_MINOR << std::endl;

	// 指定C++标准
	std::cout << "C++ 11: " << std::atof("100") << std::endl;
	// 添加库
	std::cout << "MathFunctions: " << mysqrt(192.1) << std::endl;
    return EXIT_SUCCESS;
}