g++ are compiler-drivers of the GNU Compiler Collection (which was once upon a time just the GNU C Compiler).
Even though they automatically determine which backends (
cc1plus …) to call depending on the file-type, unless overridden with
-x language, they have some differences.
The probably most important difference in their defaults is which libraries they link against automatically.
According to GCC’s online documentation link options and how g++ is invoked,
g++ is equivalent to
gcc -xc++ -lstdc++ -shared-libgcc (the 1st is a compiler option, the 2nd two are linker options). This can be checked by running both with the
-v option (it displays the backend toolchain commands being run).