Each Core Foundation opaque type has one or more creation functions, functions that create and return an object of that type initialized in a particular way. All creation functions take as their first parameter a reference to an allocator object (CFAllocatorRef
). Some functions may also have allocator parameters for specialized allocation and deallocation purposes.
You have several options for the allocator-reference parameters:
You can pass the constant kCFAllocatorSystemDefault
; this specifies the generic system allocator (which is the initial default allocator).
You can pass NULL
to specify the current default allocator (which might be a custom allocator or the generic system allocator). This is the same as passing kCFAllocatorDefault
.
You can pass the constant kCFAllocatorNull
which indicates an allocator that does not allocate—it is an error to attempt to use it. Some creation functions have a parameter for a special allocator used to reallocate or free a backing store; by specifying kCFAllocatorNull
for the parameter, you prevent automatic reallocation or deallocation.
You can get a reference to the allocator used by another Core Foundation object with the CFGetAllocator
function and pass that reference in. This technique allows you to put related objects in a memory “zone” by using the same allocator for allocating them.
You can pass a reference to a custom allocator (see “Creating Custom Allocators”).
If you are to use a custom allocator and you want to make it the default allocator, it is advisable to first get a reference to the current default allocator using the CFAllocatorGetDefault
function and store that in a local variable. When you are finished using your custom allocator, use the CFAllocatorSetDefault
function to reset the stored allocator as the default allocator.
© 2008 Apple Inc. All Rights Reserved. (Last updated: 2008-10-15)