In iOS, why objRect can be used but NSLog(@"%@", objRect) will cause bad memory access?

Question

In iOS, objRect is a CGRect object. The code runs fine with

if (objRect.origin.x > 0)  { 
    // do something 
}

but under it, the line

NSLog(@"%@", objRect);

will cause bad memory access (EXC_BAD_ACCESS) and the program will stop. Why is that? Can the object be printed out otherwise?

Answer 1

CGRect is not an Objective-C object, so it cannot respond to [objRect description] (which is what %@ means). It is a structure:

struct CGRect {
    CGPoint origin;
    CGSize size;
};
typedef struct CGRect CGRect;

If you want to log your CGRect, you can use NSStringFromCGRect.