//强制去掉警告信息
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wunused-variable"
NSString *testStr = @"test";
#pragma clang diagnostic pop
push和pop之间为忽略的范围，如果不写就是从#pragma clang diagnostic ignored "-Wunused-variable"开始忽略；
"-Wunused-variable"忽略警告的类型，要结合具体警告
