CFType Reference

Derived from
None
Framework
CoreFoundation/CoreFoundation.h
Declared in
CFBase.h
CFString.h
Companion guides
Core Foundation Design Concepts
Memory Management Programming Guide for Core Foundation

Overview

All other Core Foundation opaque types derive from CFType. The functions, callbacks, data types, and constants defined for CFType can be used by any derived opaque type. Hence, CFType functions are referred to as “polymorphic functions.” You use CFType functions to retain and release objects, to compare and inspect objects, get descriptions of objects and opaque types, and to get object allocators.

Functions by Task

Memory Management

Determining Equality

Hashing

Miscellaneous Functions

Functions

CFCopyDescription

Returns a textual description of a Core Foundation object.

CFStringRef CFCopyDescription (
   CFTypeRef cf
);
Parameters
cf

The CFType object (a generic reference of type CFTypeRef) from which to derive a description.

Return Value

A string that contains a description of cf. Ownership follows the Create Rule.

Discussion

The nature of the description differs by object. For example, a description of a CFArray object would include descriptions of each of the elements in the collection.

You can use this function for debugging Core Foundation objects in your code. Note, however, that the description for a given object may be different in different releases of the operating system. Do not create dependencies in your code on the content or format of the information returned by this function.

Availability
  • Available in iOS 2.0 and later.
Declared In
CFBase.h

CFCopyTypeIDDescription

Returns a textual description of a Core Foundation type, as identified by its type ID, which can be used when debugging.

CFStringRef CFCopyTypeIDDescription (
   CFTypeID type_id
);
Parameters
theType

An integer of type CFTypeID that uniquely identifies a Core Foundation opaque type.

Return Value

A string containing a type description. Ownership follows the Create Rule.

Discussion

You can use this function for debugging Core Foundation objects in your code. Note, however, that the description for a given object may be different in different releases of the operating system. Do not create dependencies in your code on the content or format of the information returned by this function.

Availability
  • Available in iOS 2.0 and later.
Declared In
CFBase.h

CFEqual

Determines whether two Core Foundation objects are considered equal.

Boolean CFEqual (
   CFTypeRef cf1,
   CFTypeRef cf2
);
Parameters
cf1

A CFType object to compare to cf2.

cf2

A CFType object to compare to cf1.

Return Value

true if cf1 and cf2 are of the same type and considered equal, otherwise false.

Discussion

Equality is something specific to each Core Foundation opaque type. For example, two CFNumber objects are equal if the numeric values they represent are equal. Two CFString objects are equal if they represent identical sequences of characters, regardless of encoding.

Availability
  • Available in iOS 2.0 and later.
Related Sample Code
Declared In
CFBase.h

CFGetAllocator

Returns the allocator used to allocate a Core Foundation object.

CFAllocatorRef CFGetAllocator (
   CFTypeRef cf
);
Parameters
cf

The CFType object to examine.

Return Value

The allocator used to allocate memory for cf.

Discussion

When you are creating a Core Foundation object sometimes you want to ensure that the block of memory allocated for the object is from the same allocator used for another object. One way to do this is to reuse the allocator assigned to an existing Core Foundation object when you call a “creation” function.

Availability
  • Available in iOS 2.0 and later.
Declared In
CFBase.h

CFGetRetainCount

Returns the reference count of a Core Foundation object.

CFIndex CFGetRetainCount (
   CFTypeRef cf
);
Parameters
cf

The CFType object to examine.

Return Value

A number representing the reference count of cf.

Discussion

You increment the reference count using the CFRetain function, and decrement the reference count using the CFRelease function.

This function may useful for debugging memory leaks. You normally do not use this function, otherwise.

Availability
  • Available in iOS 2.0 and later.
Declared In
CFBase.h

CFGetTypeID

Returns the unique identifier of an opaque type to which a Core Foundation object belongs.

CFTypeID CFGetTypeID (
   CFTypeRef cf
);
Parameters
cf

The CFType object to examine.

Return Value

A value of type CFTypeID that identifies the opaque type of cf.

Discussion

This function returns a value that uniquely identifies the opaque type of any Core Foundation object. You can compare this value with the known CFTypeID identifier obtained with a “GetTypeID” function specific to a type, for example CFDateGetTypeID. These values might change from release to release or platform to platform.

Availability
  • Available in iOS 2.0 and later.
Related Sample Code
Declared In
CFBase.h

CFHash

Returns a code that can be used to identify an object in a hashing structure.

CFHashCode CFHash (
   CFTypeRef cf
);
Parameters
cf

A CFType object to examine.

Return Value

An integer of type CFHashCode that represents a hashing value for cf.

Discussion

Two objects that are equal (as determined by the CFEqual function) have the same hashing value. However, the converse is not true: two objects with the same hashing value might not be equal. That is, hashing values are not necessarily unique.

The hashing value for an object might change from release to release or from platform to platform.

Availability
  • Available in iOS 2.0 and later.
Declared In
CFBase.h

CFMakeCollectable

Makes a newly-allocated Core Foundation object eligible for garbage collection.

CFTypeRef CFMakeCollectable (
   CFTypeRef cf
);
Parameters
cf

A CFType object to make collectable. This value must not be NULL.

Return Value

cf.

Discussion

For more details, see Garbage Collection Programming Guide.

Special Considerations

If cf is NULL, this will cause a runtime error and your application will crash.

Availability
  • Available in iOS 2.0 and later.
Declared In
CFBase.h

CFRelease

Releases a Core Foundation object.

void CFRelease (
   CFTypeRef cf
);
Parameters
cf

A CFType object to release. This value must not be NULL.

Discussion

If the retain count of cf becomes zero the memory allocated to the object is deallocated and the object is destroyed. If you create, copy, or explicitly retain (see the CFRetain function) a Core Foundation object, you are responsible for releasing it when you no longer need it (see Memory Management Programming Guide for Core Foundation).

Special Considerations

If cf is NULL, this will cause a runtime error and your application will crash.

Availability
  • Available in iOS 2.0 and later.
Related Sample Code
Declared In
CFBase.h

CFRetain

Retains a Core Foundation object.

CFTypeRef CFRetain (
   CFTypeRef cf
);
Parameters
cf

The CFType object to retain. This value must not be NULL

Return Value

The input value, cf.

Discussion

You should retain a Core Foundation object when you receive it from elsewhere (that is, you did not create or copy it) and you want it to persist. If you retain a Core Foundation object you are responsible for releasing it (see Memory Management Programming Guide for Core Foundation).

Special Considerations

If cf is NULL, this will cause a runtime error and your application will crash.

Availability
  • Available in iOS 2.0 and later.
Related Sample Code
Declared In
CFBase.h

CFShow

Prints a description of a Core Foundation object to stderr.

void CFShow (
   CFTypeRef obj
);
Parameters
obj

A Core Foundation object derived from CFType. If obj is not a Core Foundation object, an assertion is raised.

Discussion

The output is printed to the standard I/O standard error (stderr).

This function is useful as a debugging aid for Core Foundation objects. Because these objects are based on opaque types, it is difficult to examine their contents directly. However, the opaque types implement description function callbacks that return descriptions of their objects. This function invokes these callbacks.

Special Considerations

You can use CFShow in one of two general ways. If your debugger supports function calls (such as gdb does), call CFShow in the debugger:

(gdb) call (void) CFShow(string)
Hello World

You can also incorporate calls to CFShow in a test version of your code to print out "snapshots" of Core Foundation objects to the console.

Availability
  • Available in iOS 2.0 and later.
Related Sample Code
Declared In
CFString.h

Data Types

CFHashCode

A type for hash codes returned by the CFHash function.

typedef unsigned long CFHashCode;
Availability
  • Available in iOS 2.0 and later.
Declared In
CFBase.h

CFTypeID

A type for unique, constant integer values that identify particular Core Foundation opaque types.

typedef unsigned long CFTypeID;
Discussion

Defines a type identifier in Core Foundation. A type ID is an integer that identifies the opaque type to which a Core Foundation object “belongs.” You use type IDs in various contexts, such as when you are operating on heterogeneous collections. Core Foundation provides programmatic interfaces for obtaining and evaluating type IDs.

Because the value for a type ID can change from release to release, your code should not rely on stored or hard-coded type IDs nor should it hard-code any observed properties of a type ID (such as, for example, it being a small integer).

Availability
  • Available in iOS 2.0 and later.
Declared In
CFBase.h

CFTypeRef

An untyped "generic" reference to any Core Foundation object.

typedef const void * CFTypeRef;
Discussion

The CFTypeRef type is the base type defined in Core Foundation. It is used as the type and return value in several polymorphic functions. It is a generic object reference that acts as a placeholder for other true Core Foundation objects.

Availability
  • Available in iOS 2.0 and later.
Declared In
CFBase.h


© 2003, 2007 Apple Inc. All Rights Reserved. (Last updated: 2007-07-12)

Did this document help you? Yes It's good, but... Not helpful...