Mac OS X for Unix Geeks

Header Files

There are two types of header files in Mac OS X.

Ordinary header files

These header files are inserted into source code by a preprocessor prior to compilation. Ordinary header files have a .h extension.

Precompiled header files

These header files have a .p extension.

Header files serve four functions:

• They contain C declarations.

• They contain macro definitions.

• They provide for conditional compilation.

• They provide line control when combining multiple source files into a single file that is subsequently compiled.

Tip

The mechanism for enabling strict POSIX.1 compliance is built into the system header files. The preprocessor variables _ANSI_SOURCE, __STRICT_ANSI_ _, and _POSIX_SOURCE are supported.

Unix developers will find the ordinary header files familiar, since they follow the BSD convention. The C preprocessor directive #include includes a header file in a C source file. There are essentially three forms of this syntax:

#include < headername .h>

This form is used when the header file is located in the directory /usr/include.

#include < directory/headername .h>

This form is used when the header file is located in the directory /usr/include/ directory, where directory is a subdirectory of /usr/include.

#include " headername .h"

This form is used when the header file is located in a user or nonstandard directory. The form should either be in the same directory as the source file you are compiling or in a directory specified by cc’s -I directory switch.

You can use ...