## 检测操作系统

CMake是可以跨平台的，所以必须了解如何优雅地操作系统。

```txt
cmake_minimum_required(VERSION 3.5 FATAL_ERROR)
project(wang6)

if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
    message(STATUS "Configuring on Linux")
elseif(CMAKE_SYSTEM_NAME STREQUAL "Darwin")
    message(STATUS "Configuring on macOS")
elseif(CMAKE_SYSTEM_NAME STREQUAL "Windows")
    message(STATUS "Configuring on Windows")
elseif(CMAKE_SYSTEM_NAME STREQUAL "AIX")
    message(STATUS "Configuring on IBM AIX")
else()
    message(STATUS "Configuring on ${CMAKE_SYSTEM_NAME}")
endif()
```

测试一下项目：

```bash
mkdir -p build
cd build
cmake ..
```


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