#pragma GCC diagnostic 编译器警告

方法弃用警告

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
            backgroundConfiguration = [NSURLSessionConfiguration backgroundSessionConfiguration:self.backgroundSessionIdentifier];
#pragma GCC diagnostic pop

中间代码是弃用代码只支持iOS7-iOS8，当前编译器会报黄色警告。
当我们要支持不同版本时，为了去掉警告可以使用此方法。

不兼容指针类型

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

retain cycle

#pragma clang diagnostic push  
#pragma clang diagnostic ignored "-Warc-retain-cycles"  
    self.completionBlock = ^ {  
        ...  
    };  
#pragma clang diagnostic pop 
    #pragma clang diagnostic pop  

未使用变量

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

原文：http://blog.csdn.net/mamong/article/details/24542107
参考链接：
http://nshipster.com/pragma/
http://www.cocoachina.com/applenews/devnews/2013/0731/6707.html
看这个就行了 -》http://fuckingclangwarnings.com/