From Teknologisk videncenter
From GCC manpage
Compiling C++ Programs
C++ source files conventionally use one of the suffixes .C, .cc, .cpp, .CPP, .c++, .cp, or .cxx; C++ header files often use .hh or .H; and preprocessed C++ files use the suffix .ii. GCC recognizes files with these names and compiles them as C++ programs even if you call the com- piler the same way as for compiling C programs (usually with the name gcc).
However, the use of gcc does not add the C++ library. g++ is a program that calls GCC and treats .c, .h and .i files as C++ source files instead of C source files unless -x is used, and automatically speci- fies linking against the C++ library. This program is also useful when precompiling a C header file with a .h extension for use in C++ compi- lations. On many systems, g++ is also installed with the name c++.
When you compile C++ programs, you may specify many of the same com- mand-line options that you use for compiling programs in any language; or command-line options meaningful for C and related languages; or options that are meaningful only for C++ programs.