PATH
The precompiled version of a header file has a ".p" extension, rather than the standard ".h" extension. You should not refer to AppKit.p in your source files; just use AppKit.h and the preprocessor will use the precompiled form if it's available and appropriate.
When the preprocessor encounters an include directive, it automatically looks for a precompiled version of the header. If one is found, it checks whether the context is equivalent to the context in which the precompiled header was built--if it is, the precompiled header is used. However, if any of the following problems occur, the non-precompiled form is included instead:
Compile-time warnings (described at the end of this file) indicate the nature of any problems that occur. However, you may suppress these warning messages with -Wno-precomp . The intent of these messages is to point out problems that, if corrected, would improve compilation speed.
If you're developing a small project, you don't need to bother building your own precompiled headers--just use the precompiled system headers AppKit.p , Foundation.p , mach.p and so on. If these system precompiled header files don't exist on Mac OS X, you can create them by running the fixPrecomps utility. Also, it's easy to create your own precompiled headers if you wish to do so, however, as described in the next section.