概述
cmake是一种跨平台编译工具，除了可以编译c，c++代码也可以编译其他语言的代码，其主要就是通过cmake执行CMakeLists.txt从而生成Makefile。下面就自己了解到的简单的一点知识，做以记录。更多可查看官网：https://cmake.org。
cmake简单使用
- 创建项目文件夹。
在终端输入指令：mkdir testCmake-helloworld
- 创建项目文件及CMakeLists.txt。
在终端输入：
cd testCmake-helloworld
touch CMakeLists.txt
vim main.cpp
打开main.cpp后，在其中写入如下内容：
main.cppmain.cpp
#include <iostream>
using namespace std;
int main(int argc,char*argv[])
{
cout<<"hello world!!"<<endl;
return 0;
}
保存后退出。
终端输入：vim CMakeLists.txt
向CMakeLists.txt写入如下内容：
cmake_minimum_required(VERSION 2.8)
project(hello)
add_executable(hello main.cpp)
保存退出，查看当前的文件列表：
$ ls
CMakeLists.txt build-hello-cmake main.cpp
可以看到有两个文件CMakeLists.txt 和main.cpp，一个文件夹build-hello-cmake，此时可以进入到构建目录build-hello-cmake中，输入下述指令：
cmake ..
终端会显示如下：
CMake Deprecation Warning at CMakeLists.txt:1 (cmake_minimum_required):
Compatibility with CMake < 2.8.12 will be removed from a future version of
CMake.
Update the VERSION argument <min> value or use a ...<max> suffix to tell
CMake that the project does not need compatibility with older versions.
-- The C compiler identification is AppleClang 13.0.0.13000029
-- The CXX compiler identification is AppleClang 13.0.0.13000029
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /Users/admin/Program/testCmake-helloworld/build-hello-cmake
接着终端输入：
make
终端显示如下：
[ 50%] Building CXX object CMakeFiles/hello.dir/main.cpp.o
[100%] Linking CXX executable hello
[100%] Built target hello
此时构建完成，在目录build-hello-cmake中生成可执行程序hello。当前路径下执行下述指令：
# admin @ bogon in ~/Program/testCmake-helloworld/build-hello-cmake [17:21:33]
$ ./hello
hello world!!
会输出程序的运行结果。
上述是cmake执行构建的过程，总体来说就是下列指令：
mkdir 构建目录名
cd 构建目录名
cmake CMakeLists.txt所在的路径
make
其构建项目最常用的四句指令就是上述所写。首先在项目目录下创建一个空文件夹，作为构建目录，即：mkdir 构建目录名;然后进入构建目录，即：cd 构建目录名；接下来执行cmake,但是在cmake的后面需要指明CMakeLists.txt所在的路径，最后执行make指令，整个项目生成可执行程序。
当不在构建目录里执行cmake时，可以按照下述方法来执行cmake:
admin @ bogon in ~/Program/testCmake-helloworld [17:31:29]
$ cmake -S ./ -B ./build-hello-cmake
CMake Deprecation Warning at CMakeLists.txt:1 (cmake_minimum_required):
Compatibility with CMake < 2.8.12 will be removed from a future version of
CMake.
Update the VERSION argument <min> value or use a ...<max> suffix to tell
CMake that the project does not need compatibility with older versions.
-- The C compiler identification is AppleClang 13.0.0.13000029
-- The CXX compiler identification is AppleClang 13.0.0.13000029
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /Users/admin/Program/testCmake-helloworld/build-hello-cmake
其中-S指明了源文件所在的路径，-B指明了构建生成的文件所在的路径。
这样就可以在非构建目录下执行cmake，但生成的文件依旧存入到构建目录中。同样接下来也在项目目录下使用指令make,指令如下：
# admin @ bogon in ~/Program/testCmake-helloworld [17:33:09]
$ make -C ./build-hello-cmake
[ 50%] Building CXX object CMakeFiles/hello.dir/main.cpp.o
[100%] Linking CXX executable hello
[100%] Built target hello
make指令中-C指明了生成可执行文件所在的路径。
以上仅供参考。
