方法棄用警告

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

中間代碼是棄用代碼只支持iOS7-iOS8，當前編譯器會報黃色警告。
當我們要支持不同版本時，為了去掉警告可以使用此方法。

不兼容指針類型

    #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  

未使用變量

#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
參考鏈接：
http://nshipster.com/pragma/
http://www.cocoachina.com/applenews/devnews/2013/0731/6707.html
看這個就行了 -》http://fuckingclangwarnings.com/