What is a header file?

Most C programmers are already quite familiar with header files. These are also frequently referred to as " .h " (pronounced "dot h") files because the filename usually has a .h suffix. When a large program is designed, the header file is used to store information that several routines within the program will want to address. For example, the programmer might want to define some common constants in a header file. He might also place commonly used structures in the header file as well as some external variables and function declarations. Macros are also commonly defined in header files.

The source for the routines that will use or include the information from the header file will begin with #include statements, at the head of the source ”thus the name header file. Header files can also use the #include statement to bring in other header files at compilation.