#pragma 处理警告

首先#pragma在本质上是声明,常用的功能就是注释,尤其是给Code分段注释;而且它还有另一个强大的功能是处理编译器警告,但却没有上一个功能用的那么多。

clang diagnostic 是#pragma 第一个常用命令:

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-相关命令"
    // 你自己的代码
#pragma clang diagnostic pop

常见的用法

1. 方法弃用告警

#pragma clang diagnostic push  
#pragma clang diagnostic ignored "-Wdeprecated-declarations"      
[TestFlight setDeviceIdentifier:[[UIDevice currentDevice] uniqueIdentifier]];  
#pragma clang diagnostic pop

2. 不兼容指针类型

#pragma clang diagnostic push   
#pragma clang diagnostic ignored "-Wincompatible-pointer-types"  
   //  
#pragma clang diagnostic pop

3. 循环引用

// completionBlock is manually nilled out in AFURLConnectionOperation to break the retain cycle.  
#pragma clang diagnostic push  
#pragma clang diagnostic ignored "-Warc-retain-cycles" 
    self.completionBlock = ^ {  
        ...  
    };  
#pragma clang diagnostic pop

4. 未使用变量

#pragma clang diagnostic push   
#pragma clang diagnostic ignored "-Wunused-variable"  
    int a;   
#pragma clang diagnostic pop

#pargma 用法详情:

  1. http://nshipster.cn/pragma/
  2. http://nshipster.com/clang-diagnostics/
  3. http://fuckingclangwarnings.com/
  4. http://clang.llvm.org/docs/UsersManual.html#diagnostics_pragmas

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