-Wall
Show all warnings.
-Werror
Show warnings as errors.
-fsyntax-only
Check the code for syntax errors, but don't do anything beyond that.
-pedantic
Issue all the warnings demanded by strict ISO C, reject all programs that use forbidden extensions, and some other programs that do not follow ISO C. Valid ISO C programs should compile properly with or without this option (though a rare few will require -ansi or a -std option specifying the required version of ISO C). However, without this option, certain GNU extensions and traditional C features are supported as well. With this option, they are rejected.
-pedantic-errors
Pedantic warnings are produced as errors.
-w
Inhibit all warning messages.