c++ - OSX - replace gcc version 4.2.1 with 4.9 installed via Homebrew

Question

This has been plaguing me for awhile now. I am trying to compile a huge C++ file (I know it works as I it works fine on my Arch Linux computer at work). When I checked my GCC version on my mac It returns the following

Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 6.0 (clang-600.0.57) (based on LLVM 3.5svn)
Target: x86_64-apple-darwin14.1.0
Thread model: posix

I have also installed the most recent GCC version using Homebrew with

brew install gcc49

My question now is how do I apply that newly installed GCC version to be the default version that the terminal uses?

I am also aware that when you use homebrew to isntall gcc it names it gcc-49 so that there is no confusion between packages.

I have no idea how to replace the 4.2.1 version that comes with XCode with the 4.9 version I have installed.

Thanks

Edit: Switched to my mac to get the full return statement of gcc --version

Edit 2: My end game here is to be able to navigate to the directory and be able to type

make
sudo make install

to install the daemon that has been made. Right now that returns tons of errors with random packages and the Standard Library

Answer 1

By default, homebrew places the executables (binaries) for the packages it installs into /usr/local/bin - which is a pretty sensible place for binaries installed by local users when you think about it - compared to /bin which houses standardisded binaries belonging to the core OS. So, your brew command should have installed gcc-4.9 into /usr/local/bin. The question is now how to use it... you have several options.

Option 1

If you just want to compile one or two things today and tomorrow, and then probably not use the compiler again, you may as well just invoke the gcc installed by homebrew with the full path like this:

/usr/local/bin/gcc-4.9 --version

Option 2

If you are going to be using gcc quite a lot, it gets a bit tiresome explicitly typing the full path every time, so you could put the following into your ~/.bash_profile

export PATH=/usr/local/bin:$PATH

and then start a new Terminal and it will know it needs to look in /usr/local/bin, so you will be able to get away with simply typing

gcc-4.9 --version

Option 3

If you just want to use gcc to invoke the compiler, without worrying about the actual version, you can do Option 2 above and additionally create a symbolic link like this

cd /usr/local/bin
ln -s  gcc-4.9  gcc

That will allow you to run the homebrew-installed gcc by simply typing gcc at the command line, like this

gcc --version

Note:

If you later want to install, say gcc-4.13 or somesuch, you would do your brew install as before, then change the symbolic link like this:

cd /usr/local/bin
rm gcc               # remove old link from gcc to gcc-4.9
ln -s gcc-4.13 gcc   # make new link from gcc to gcc-4.13

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Note that if you are actually using C++ rather than C, you will need to adapt the above for g++ in place of gcc.