What does the version number of gcc mean ?

[John Love-Jensen]

Hi d hongqian,

> I want to know  the version of gcc 's  mean. For example: the gcc
> 3.4.6, what's the difference between the 3.4.6 and 3.4.5.
> and what's difference between 3.3.0 and 3.2.0 and  what's the
> difference between 3.0.0 and 4.0.0.

Look at the GCC release notes.

Using Google (for example), search for:
release notes site:gcc.gnu.org

> If I want to update my gcc, how many things should also be update
> so that the system could be stable.

q.v.:
http://gcc.gnu.org/install/prerequisites.html

HTH,
--Eljay