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.
Last updated: 2009-10-21