Question

I am trying to debug a particular function in my application but am finding it tricky as the local variables are not showing up, nor is the code execution progressing line by line. Instead, it appears to hop around a bit and many of my locally scoped variables are not visible in the debugging area.

The function is called from an assetForURL result block.

I would expect some of this behavior with optimizations on, but I turned them off and have the same problem. Here is some of the code, just in case that may be the cause.

{
UIImageView* newImage = [[tvVC imageViewArray] objectAtIndex:viewIndex];
UIImageView* oldImage = [[tvVC imageViewArray] objectAtIndex:((viewIndex + 1) % 2)];

[newImage setImage:image];
[newImage setBounds:CGRectMake(0, 0, image.size.width, image.size.height)];         
[newImage setTransform:CGAffineTransformMakeScale(scalar * minScalar, scalar * minScalar)];
CGPoint adjust = [scrollView contentOffset];
CGPoint curCenter = [oldImage center];
NSLog(@" offset %f, %f   center %f, %f",adjust.x, adjust.y, curCenter.x, curCenter.y);
}

What kills me is that the NSLog prints valid results, but if I try and step through, I can’t actually inspect the adjust or curCenter elements manually.

Compiling using Apple LLVM 3.1

Thanks,

Answer 1

A weekend away and a fresh mind helped with this issue.

In the end, I switched to GDB debugging versus LLDB. This resulted in a much more useful error message, ‘variable optimized away by the compiler’. I guess even with optimizations off, the compiler will get rid of stupid variables that aren’t really needed. (I only added them to make debugging more clear to me, I realize they are not necessary for the code)

Once that was established, I just identified the adjust and curCenter as ‘volatile’ and the issue was resolved. I do still see a little hopping around in the code execution, but I am chalking that up to other optimizations