A header file is a file containing C declarations and macro definitions (see Macros) to be shared between several source files. You request the use of a header file in your program with the C preprocessing directive `#include'.
| Header Uses | What header files are used for. |
| Include Syntax | How to write `#include' directives. |
| Include Operation | What `#include' does. |
| Once-Only | Preventing multiple inclusion of one header file. |
| Inheritance | Including one header file in another header file. |