print in Xcode GDB with C++ doesn't print correct values

Question

I'm writing/debugging an iPhone project that uses a large portion of C++ for image processing. I'm having trouble when I'm using gdb under Xcode because whenever I print values, they are completely out of whack with the true values (comparing
cout << "width" << width << endl; prints out 320, and if I do a
print width in gdb, I get values like 805300460)

I'm guessing it's a problem with gdb, not with the program, since I don't think I'm overwriting memory and values printed to stdout seem correct. The language is auto-set to be C++.

Looking at this Apple GDB doc it seems like adding this compiler flag might help -gdwarf-2? Not sure where to do so.

Anybody run into this problem? Have any ideas?

Answer 1

At a quick stab, what optimizations are you using? If you're using some, there's the possibility that the value is being kept in a register and not being written to memory just then, and so you'd be getting whatever value used to be in memory. In this case, you'd get the correct answer through the iostream, since the compiler has to make observable behavior match what the language says, but gdb looks behind the scenes.

Answer 2

In gdb try:

p /d width

Perhaps encoding is different.

I do not think that "dwarfs" params will help. Dwarf params describe intermediate code with source code during compilation. Basically they try to preserve source code during compilation phases. In gdb it allows you to match line number from source code to binary statments. That issue shouldn't have anything to do with variables.