7.6.4 Options for Controlling Warnings and Errors

Warnings are diagnostic messages that report constructions that are not inherently erroneous but that are risky or suggest there may have been an error.

You can request many specific warnings with options beginning -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.