Question

When seeing an instance variable’s address in the debugger, how can one get the class by entering in the given memory address?

I know that the opposite (getting the address from an instance) is possible with p someObjectInstance in the debugger or NSLog(@"%p", someObjectInstance); from within the code. Is there a similar way to do this the other way around?

Answer 1

What you are asking for is VERY unsafe. Accessing an unknown memory location is generally a bad idea, but since you asked:

EDIT: If inside gdb or lldb, you can do the following:

po [(id)(0xDEADBEEF) class]

If running from code, however, use the following;

NSString *input = @"0xFAFAFA";

unsigned address = UINT_MAX; // or UINT_MAX
[[NSScanner scannerWithString:input] scanHexInt:&address];

if (address == UINT_MAX)
{
    // couldn't parse input...
    NSLog(@"failed to parse input");
    return 0;
}

void *asRawPointer = (void *) (intptr_t) address;
id value = (__bridge id) asRawPointer;

// now do something with 'value'
NSLog(@"%@", [value class]);