Question

I’m working on a project that has C code embedded within Objective-C code. The C code produces some void * pointers that I would like to pass between Objective-C methods, so I’d like to wrap them in Objective-C objects to make an NSSet or something to that effect.

I have looked into NSData, which seems to accept arbitrary data, but wants to know the length of the memory chunk, that I don’t have.

Any help is appreciated.

Answer 1

The NSValue class is usually used for this task:

NSValue* value = [NSValue valueWithPointer: myPointer];

and

void* myPointer = [value pointerValue];

Note, though, that the pointer given will not receive any special treatment with respect to memory management. You (and you alone) are responsible for making sure, that the memory it points to remains valid as long as pointers to that memory region exist and are reachable in some part of your program.

Note, though, that using such a value with NSSet or as key in a NSDictionary might or might not yield the intended effect:

NSData is essentially a byte buffer. It actually represents the content of the memory in question. Comparing NSData instances for equality compares at byte level. This is one of the reasons, NSData needs to know about the length of the memory region in question.

NSValue with a pointer value is an entirely different beast. Here, that actual (numeric) pointer value is the essential thing. No consideration is given (when comparing two NSValue instances) to the actual content at the address.