Finding the compiler version in your Unix system should be the first step before you attempt to compile any package from its source codes. In fact, if you're familiar with the common compilation routine, the configure script which you run to generate the Makefile before compiling anything does exactly that – it finds out which compilers (if any) you have installed on your system, and confirms their versions and capabilities.
If you want to find the compiler version yourself, here's what you do:
1) Confirm which compiler you're looking at
Most likely, it will be gcc, but since GCC isn't a GNU C Compiler anymore, but a GNU Compiler Collection, it can stand for any programming language from this suite. Here they are, just so that you know (a binary of each compiler is shown in bold):
gcc – GNU project C and C++ compiler
g++ – GNU project C and C++ compiler
gcj – GNU Compiler for Java
g77 – GNU project Fortran 77 compiler
gnat – GNU Ada Translator
2) Find where your compiler is installed
You have a pretty good chance of finding gcc binaries right under /usr/bin directory on most modern systems. Some older Unix distros will not have GCC installed by default, others like recent versions of Solaris and OpenSolaris, will have gcc under a different location. In Solaris 10, gcc binaries are under /usr/sfw/bin directory.
If the gcc binary isn't found, consider looking for the file using the find command, or query software repository to confirm if it's installed or now.
3) Run the compiler to find out its version
Most compilers will give you their version if -v option is specified:
$ gcc -v Using built-in specs. Target: x86_64-linux-gnu Configured with: ../src/configure -v --enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --enable-nls --program-suffix=-4.1 --enable-__cxa_atexit --enable-clocale=gnu --enable-libstdcxx-debug --enable-mpfr --enable-checking=release x86_64-linux-gnu Thread model: posix gcc version 4.1.2 (Ubuntu 4.1.2-0ubuntu4)