Advanced Mac OS X Programming: The Big Nerd Ranch Guide

Permission-Check Algorithms

Here is a quick overview of how permissions interact with the file operations discussed earlier:

• You must have read permission to open a file for reading with O_RDONLY or O_RDWR.

• You must have write permission to open a file for writing with O_WRONLY and O_RDWR.

• You must have write permission to O_TRUNC a file.

• You must have write and execute permission on a directory to create a new file. You need write permission so you can modify the directory entry, and you need execute permission so the directory can be searched.

• You must have write and execute permission on a directory to delete a file. You do not actually need read/write permissions on the file itself because the operation just manipulates the directory’s ...