I've got some code written by someone else, which has
g++ -W -Wall foobar.cc
gcc is not indicting -W is an unknown option. The gcc documentation says
-w
(lower case) is to suppress all warnings, but I can't find -W (upper case)
documented.
The index gets you to
http://gcc.gnu.org/onlinedocs/gcc-4.5.1/gcc/Warning-Options.html#index-W-236
-Wextra
This enables some extra warning flags that are not enabled by -Wall.
(This option used to be called -W. The older name is still supported,
but the newer name is more descriptive.)
Most people still use -W, it's so nice and short ;-)
Segher