CMake 基础学习

CMake 简介

CMake 是一个跨平台、开源的构建系统，一个集软件构建、测试、打包于一身的软件。它使用与平台和编译器独立的配置文件来对软件编译过程进行控制。

一 初识CMake

使用一个十分简单的例子：
在新建的项目文件夹下，建立如下两个文件

$ tree
.
├── CMakeLists.txt
└── main.cpp

CMakelists.txt 中的文件内容如下

# Set the minimum version of CMake that can be used
# To find the cmake version run
# $ cmake --version
cmake_minimum_required(VERSION 3.5)

# Set the project name
project (hello_cmake)

# Add an executable
add_executable(hello_cmake main.cpp)

main.cpp 中是一个简单的C++程序

#include<iostream>
using namespace std;
int main(){
    
    cout <<" hello word !"<<endl;
    return 0;
}

关于CMakelists.txt 中的内容后面再解释，我们先将整个程序编译运行出来。

二进制目录

运行cmake命令 的根文件夹或者顶级文件夹称为 CMAKE_BINARY_DIR，是所有二进制文件的根文件夹。CMake 及支持就地构建和生成二进制文件，也支持在源代码外构建和生成二进制文件。

就地构建

就地构建会在源代码所在的文件夹生成所有的临时文件，使得源代码和临时文件都混在一起，这样会很不方便。
我们执行 cmake . 命令， 注意符号 “ . ” 表示在当前目录执行。

$ cmake .
-- The C compiler identification is GNU 7.3.0
-- The CXX compiler identification is GNU 7.3.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /home/panlichen/miniconda3/envs/oneflow-dev-gcc7-v2/bin/x86_64-conda_cos6-linux-gnu-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: /home/panlichen/miniconda3/envs/oneflow-dev-gcc7-v2/bin/x86_64-conda_cos6-linux-gnu-c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /home/panlichen/zrk/hello_cmake

$ tree
.
├── CMakeCache.txt
├── CMakeFiles
│   ├── 3.18.2
│   │   ├── CMakeCCompiler.cmake
│   │   ├── CMakeCXXCompiler.cmake
│   │   ├── CMakeDetermineCompilerABI_C.bin
│   │   ├── CMakeDetermineCompilerABI_CXX.bin
│   │   ├── CMakeSystem.cmake
│   │   ├── CompilerIdC
│   │   │   ├── a.out
│   │   │   ├── CMakeCCompilerId.c
│   │   │   └── tmp
│   │   └── CompilerIdCXX
│   │       ├── a.out
│   │       ├── CMakeCXXCompilerId.cpp
│   │       └── tmp
│   ├── cmake.check_cache
│   ├── CMakeDirectoryInformation.cmake
│   ├── CMakeOutput.log
│   ├── CMakeTmp
│   ├── hello_cmake.dir
│   │   ├── build.make
│   │   ├── cmake_clean.cmake
│   │   ├── DependInfo.cmake
│   │   ├── depend.make
│   │   ├── flags.make
│   │   ├── link.txt
│   │   └── progress.make
│   ├── Makefile2
│   ├── Makefile.cmake
│   ├── progress.marks
│   └── TargetDirectories.txt
├── cmake_install.cmake
├── CMakeLists.txt
├── main.cpp
└── Makefile

8 directories, 28 files

可见已经成功生成了makefile文件，接下来我们make一下，并执行

$ make
$ ./hello_cmake
 hello word !

当修改代码时，没有增减源文件修改CMakeLists.txt 只需要重新make

源外构建 （推荐）

使用源外构建，你可以创建单个生成文件夹，该文件夹可以位于文件系统的任何位置。所有临时构建的目标文件都位于此目录中，以保持源码目录结构的整洁。

我们创建一个build 文件夹，在build 文件夹下执行 命令：
cmake + CMakeLists.txt 所在路径

$ tree ..
..
├── build
├── CMakeLists.txt
└── main.cpp


$ cmake .. 
-- The C compiler identification is GNU 7.3.0
-- The CXX compiler identification is GNU 7.3.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /home/panlichen/miniconda3/envs/oneflow-dev-gcc7-v2/bin/x86_64-conda_cos6-linux-gnu-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: /home/panlichen/miniconda3/envs/oneflow-dev-gcc7-v2/bin/x86_64-conda_cos6-linux-gnu-c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /home/panlichen/zrk/hello_cmake/build

$ make
Scanning dependencies of target hello_cmake
[ 50%] Building CXX object CMakeFiles/hello_cmake.dir/main.cpp.o
[100%] Linking CXX executable hello_cmake
[100%] Built target hello_cmake

$ ./hello_cmake 
 hello word !

源外构建后，目录结构如下

$ tree ..
..
├── build
│   ├── CMakeCache.txt
│   ├── CMakeFiles
│   │   ├── 3.18.2
│   │   │   ├── CMakeCCompiler.cmake
│   │   │   ├── CMakeCXXCompiler.cmake
│   │   │   ├── CMakeDetermineCompilerABI_C.bin
│   │   │   ├── CMakeDetermineCompilerABI_CXX.bin
│   │   │   ├── CMakeSystem.cmake
│   │   │   ├── CompilerIdC
│   │   │   │   ├── a.out
│   │   │   │   ├── CMakeCCompilerId.c
│   │   │   │   └── tmp
│   │   │   └── CompilerIdCXX
│   │   │       ├── a.out
│   │   │       ├── CMakeCXXCompilerId.cpp
│   │   │       └── tmp
│   │   ├── cmake.check_cache
│   │   ├── CMakeDirectoryInformation.cmake
│   │   ├── CMakeOutput.log
│   │   ├── CMakeTmp
│   │   ├── hello_cmake.dir
│   │   │   ├── build.make
│   │   │   ├── cmake_clean.cmake
│   │   │   ├── CXX.includecache
│   │   │   ├── DependInfo.cmake
│   │   │   ├── depend.internal
│   │   │   ├── depend.make
│   │   │   ├── flags.make
│   │   │   ├── link.txt
│   │   │   ├── main.cpp.o
│   │   │   └── progress.make
│   │   ├── Makefile2
│   │   ├── Makefile.cmake
│   │   ├── progress.marks
│   │   └── TargetDirectories.txt
│   ├── cmake_install.cmake
│   ├── hello_cmake
│   └── Makefile
├── CMakeLists.txt
└── main.cpp

9 directories, 32 files