Question

The method has “Get” in it’s name and doesn’t return something via return. It takes a pointer for example to a CFStringRef, like this:

CFStringRef outValue;
UInt32 propertySize = sizeof(outValue);
AudioSessionGetProperty(propertyID, &propertySize, &outValue);

The documentation says that the function “copies” the value into the the provided outValue pointer.

So this is creating an object with a +1 retain count, and I am responsible for releasing / freeing that data?

Answer 1

According to the documentation for AudioSessionGetProperty, it depends on whether the property you are getting is a C type or if it is a core foundation value:

Some Core Audio property values are C types and others are Core Foundation objects:

If you call this function to retrieve a value that is a Core
Foundation object, then this function—despite the use of “Get” in its
name—duplicates the object. You are responsible for releasing the
object, as described in “The Create Rule” in Memory Management
Programming Guide for Core Foundation.

So if what you are getting is a core foundation property value, you will need to make sure to release the resulting object.

Note that using ARC will not automatically take care of this for you. From the ARC programming guide:

In many Cocoa applications, you need to use Core Foundation-style
objects, whether from the Core Foundation framework itself (such as
CFArrayRef or CFMutableDictionaryRef) or from frameworks that adopt
Core Foundation conventions such as Core Graphics (you might use types
like CGColorSpaceRef and CGGradientRef).

The compiler does not automatically manage the lifetimes of Core
Foundation objects; you must call CFRetain and CFRelease (or the
corresponding type-specific variants) as dictated by the Core
Foundation memory management rules (see Memory Management Programming
Guide for Core Foundation).

If you cast between Objective-C and Core Foundation-style objects, you
need to tell the compiler about the ownership semantics of the object
using either a cast (defined in objc/runtime.h) or a Core
Foundation-style macro (defined in NSObject.h):