Mac OS X Tiger for Unix Geeks, 3rd Edition

Chapter 12. Libraries, Headers, and Frameworks

This chapter discusses the linking phase of building Unix-based software under Mac OS X, in particular, header files and libraries.

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 .h.gch 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 POSIX.4 compliance is built into the system header files. The preprocessor variables _ANSI_SOURCE, _ _STRICT_ANSI_ _, and _POSIX_SOURCE are supported. Because Mac OS X itself is not POSIX.4 compliant, you cannot achieve strict POSIX.4 compliance. Using these mechanisms, however, is best way to approximate POSIX.4 compliance.

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/ ...