1.9 — Header files. Code files (with a .cpp extension) are not the only files commonly seen in programs.
The other type of file is called a header file, sometimes known as an include file. Header files almost always have a .h extension. The purpose of a header file is to hold declarations for other files to use. Using standard library header files. Using g++ Most of this document was taken nearly verbatim from Paul Hilfinger.
Any errors introduced, however, are David Wolfe's. Introduction GNU provides are a publicly-available optimizing compilers (translator) for C, C++, Ada 95, and Objective C that currently runs under various implementations of Unix (plus VMS as well as OS/2 and perhaps other PC systems) on a variety of processors too numerous to mention.
C++ How to compile a c++ header file.