"g++" and "c++" compiler

g++ is the gnu c++ compiler where c++ is the system c++ compiler, in the case of ubuntu C++ is a link to g++ however in another system it could very well be a link to a non gcc compiler. as someone else said vi vs vim. just because a link to vi exists on the system doesn't mean that it's vim could be any vi clone.

On my machine, c++ is a link:

$ readlink /usr/bin/c++
/etc/alternatives/c++
$ readlink /etc/alternatives/c++
/usr/bin/g++

So c++ is just a link to g++.

This is typical Ubuntu symlink mayhem.

If you ls -l /usr/bin/c++, you will see it is actually a symbolic link. to:

/etc/alternatives/c++

Which in turn, is also a symbolic link to:

/usr/bin/g++

So, on Ubuntu systems, c++ is g++. The reasoning behind the link indirection is that there are multiple packages that could provide a c++ compiler (such as different versions of g++). You'll see this a lot on Ubuntu. For example, qmake is a link to a file in /etc/alternatives, which is (on my system) a link back to /usr/bin/qmake-qt3.

c++ is a standard name of a C++ compiler on a system.

On a GNU system you almost surely have GCC (GNU compiler collection) installed, which includes a C++ compiler named g++ ('g' for GNU). But to be POSIX-compatible, they install this compiler as c++ also, sometimes c++ is a symbolic link to g++ sometimes it's a hard link, sometimes it's just the same file installed twice.

This can be not the case for other systems like FreeBSD or NetBSD. It's possible that those systems don't have GCC (and other GNU stuff) installed.

On my system these two files are just identical:

% diff `which c++` `which g++`
% echo $?
0

This means that c++ at least invokes the same compiler, but theoretically it can interpret some command line options differently or have some different defaults. Someone with more knowledge is free to extend the answer in this regard.