The header file fcntl.h.h contains several functions that are useful for porting a program from UNIX. These functions are similar to the functions in many UNIX libraries. However, since the UNIX and Macintosh operating systems have some fundamental differences, they cannot be identical. The descriptions of the functions tell you what the differences are.

Generally, you don't want to use these functions in new programs. Instead, use their counterparts in the native API.

If you're porting a UNIX or DOS program, you might also need the functions in other UNIX compatibility headers.

"POSIX Functionality," for information on POSIX naming convetions.