When running gcc(1), -Wall is the CommandLine option that maximises warnings Generally the first thing that people look for when debugging or helping others with C/C++ code it that it is compiling with -Wall.

-Wall warns about a great many things which are normally harmless in normal circumstances but can be dangerous at others. -pedantic warns against things that are technically wrong but cannot lead to problems for gcc(1) and -pedantic-errors issues errors for such quibbles. -pedantic and -pedantic-errors are not usually used unless the code is being written with the intention of porting it to exotic hardware.