你可以使用'-W'开始的选项来请求许多特定的警告，例如-Wimplicit要求对隐式声明发出警告。所有这些特定的警告选项也有一个以“-Wno-“开头的否定形式来关闭警告;例如︰-Wno-explicit。
来源：https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html
You can request many specific warnings with options beginning with ‘-W’, for example -Wimplicit to request warnings on implicit declarations. Each of these specific warning options also has a negative form beginning ‘-Wno-’ to turn off warnings; for example,
-Wno-implicit. This manual lists only one of the two forms, whichever is not the default. For further language-specific options also refer to C++ Dialect Options and Objective-C and Objective-C++ Dialect Options.