CFMutableData manages dynamic binary data. The basic interface for managing binary data is provided by CFData. CFMutableData adds functions to modify the contents of a binary data object.
CFMutableData is “toll-free bridged” with its Cocoa Foundation counterpart,
NSMutableData. What this means is that the Core Foundation type is interchangeable in function or method calls with the bridged Foundation object. In other words, in a method where you see an
NSMutableData * parameter, you can pass in a
CFMutableDataRef, and in a function where you see a
CFMutableDataRef parameter, you can pass in an
NSMutableData instance. This also applies to concrete subclasses of
NSMutableData. See Toll-Free Bridged Types for more information on toll-free bridging.