How do I get the int value from object_getIvar(self, myIntVar) as it returns a pointer

Question

if the variable in object_getIvar is a basic data type (eg. float, int, bool) how do I get the value as the function returns a pointer (id) according to the documentation. I've tried casting to an int, int* but when I try to get that to NSLog, I get error about an incompatible pointer type.

Answer 1

It's probably boxing the value in an NSNumber. You can verify this by NSLogging the returned id's className, like so:

id returnedValue = object_getIvar(self, myIntVar);
NSLog(@"Class: %@", [returnedValue className]);

Edit: I found another question just like this one here: http://stackoverflow.com/questions/1216262

From my own experimentation, it would appear that my original assumption was incorrect. int and float and other primitives appear to be returned as the actual value. However, it would be appropriate to use ivar_getTypeEncoding to verify that the returned value is the type that you're expecting it to be.

Answer 2

you can use object_getInstanceVariable directly: (haven't tested it)

void *ptr_to_result;
object_getInstanceVariable(obj, "intvarname", &ptr_to_result);
float result = *(float *)ptr_to_result;

Answer 3

The value that is returned is the value from the right place in the object; just not the right type. For int and BOOL (but not float), you could just cast the pointer to an int or BOOL, since pointers and ints are the same size and they can be cast to each other:

(int)object_getIvar(obj, myIntVar)

Answer 4

Getting:

myFloat = 2.34f;

float myFloatValue;
object_getInstanceVariable(self, "myFloat", (void*)&myFloatValue);

NSLog(@"%f", myFloatValue);

Outputs:

2.340000

Setting:

float newValue = 2.34f;
unsigned int addr = (unsigned int)&newValue;

object_setInstanceVariable(self, "myFloat", *(float**)addr);

NSLog(@"%f", myFloat);

Outputs:

2.340000