使用pragma消除警告 (绝不可强行消除，因为有可能是个运行时错误)

#pragma clang diagnostic push

#pragma clang diagnostic ignored "命令字符串"

    代码块

#pragma clang diagnostic pop

1. "-Warc-performSelector-leaks" performselector可能造成内存泄漏

    SEL sel = @selector(gl_getImage:);

    [self performSelector:sel withObject:nil];

    以上警告也可使用消除

    IMP imp = [app methodForSelector:sel];

    void (*func)(id , SEL ,NSInteger) = (void *)imp;

    func(app,selector,0);

2. "-Wreceiver-is-weak" 调用者接收者是weak属性

3. "-Wunused-variable" 变量未使用

    或者 __unused int m = 2; //Unused variable 'm'

4. "-Wdeprecated-declarations" 方法弃用

    [UIAlertView alertView........]

5. "-Warc-retain-cycles" 循环引用

    while(true){}

6. "-Wincompatible-pointer-types" 指针不兼容的

7. "-Wundeclared-selector" 方法在本类中未申明

   eg. SEL sel = @selector(gl_getImage)

   不过以上方法导致的警告也可使用runtime机制消除

       SEL sel = sel_registerName("gl_getImage:")

       SEL sel = NSSelectorFromString(@"gl_getImage:");

8. "-Wunreachable-code" 代码将永不被执行

    NSLog(@"m");

    return;

    NSLog(@"n"); //Code will never be executed

如果想将项目中所有某类型的警告都消除

11. 配置文件 buildSettings->Other Warning Flags

    加入配置字符

    11.1 code will never be executed

        -Wno-unreachable-code   全局禁用警告

        -Wunreachable-code      全局启用警告

    11.2 Unused Entity Issue / unused function 'xxxxx'

        -Wno-unused-function    全局禁用

        -Wunused-function       全局启用

    11.3 ......