.h files are C programming source "headers".

These are files containing pre-processor (cpp) directives such as #define and #include; they declare function prototypes without defining (implementing) the functions, and define macros. They may also include some conditional definitions or inclusions. Functions and programs are defined (implemented) in .c files. They are compiled into .o (object) files which are, in turn, linked into .a (library archives) or .so (shared object libraries — like MS-Windows .DLLs) or executable binary files (usually having no filename extensions under UNIX/Linux).

Header files also become part of the standard API (applications programming interface) to the libraries that implement them. Thus it is commonly required to have .h files under /usr/include to provide the macro definitions and function prototypes for libraries under /usr/lib in order to compile programs at all. These are thus part of the programming "tool chain" on any UNIX/Linux system.

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• () JimDennis - 23 Sep 2003
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Revision Comment

• 24 Sep 2003 — typos, minor reformatting
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