I would like to install a specific version of gdb and gcc with macports on mac os x leopard, not the last one, but the 6.8 for gdb. Is it possible?
It is possible. It's just convoluted and tedious. It's listed in the documentation these days.
Steps
Go to macports trac and find the package you're looking for. This is the link for subversion, which is the package I'll be using in the example.
Click the PortFile
Click Revision Log (top right)
Pour through the revisions until you find the version you're looking for. Remember the revision number.
In this example I'm looking for version 1.7 of subversion.
With that revision number noted. You need to checkout the version of that subdirectory at that revision.
cd /tmp
svn co http://svn.macports.org/repository/macports/trunk/dports/devel/subversion --revision 106629
Then cd into the folder and run the install
cd subversion
sudo port install
Then it should become selected by default. You can check with
sudo port installed subversion
The following ports are currently installed:
subversion @1.7.10_0 (active)
subversion @1.8.8_0
subversion @1.8.10_0