How to find out which ANSI C standard my gcc works with by default?

Question

I read here it is C90 with extensions. How can I know for sure?

Answer 1

Read the manpage. On my computer (OSX 10.7, gcc version 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2335.15.00)):

-std=
        Determine the language standard. This option is currently only supported
        when compiling C or C++.

        A value for this option must be provided; possible values are

....

        gnu89
                Default, ISO C90 plus GNU extensions (including some C99 features).

....

        gnu++98
                The same as -std=c++98 plus GNU extensions. This is the default for C++ code.