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

You can also check one of the predefined Macros, for example whether your GCC asks for ANSI C (STRICT__ANSI) by default (i.e. without any cli arguments).

Answer 2

Use the -std= flag to specify a language dialect: c89, c99, c++98, etc. Note that c90 is equivalent to c89.

As a shorthand -ansi causes -std=c89 in C mode and -std=c++98 in C++ mode.

Use -pedantic to enable all diagnostics that the standards require.

The defaults are gnu89 for C and gnu++98 for C++. Consult the manual for detailed descriptions of the various dialects.

Answer 3

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.

Answer 4

Try below command and search for std

gcc -v --help | less

It will show you all the available options for your gcc.