not able to use g++ from Fedora
gcc-c++ is not installed.
The yum list command shows all packages, not just the installed packages. The packages that are installed are prefixed with an ampersand or "@" sign. The packages that are not installed (but are available to be installed) lack the ampersand.
To see what is installed try the command rpm -qa. Or in your example rpm -qa | grep gcc
Oddly enough, if you didn't just grep for gcc, you would have been able to see the "Installed packages" and "Available packages" output lines between the two sets.