Xcode - scribble, guard edges and guard malloc

Question

Can someone explain what do these options in Xcode do?

• Enable Scribble
• Enable Guard Edges
• Enable Guard Malloc

what they are an

Answer 1

The "documentation" link above is to Xcode in general, but more specifically RN-MallocOptions covers these (and other) options in detail.

Jim Kubicek shows a nice example in Debugging Smashed Memory in Obj-C, including the important "How do I enable these in Xcode?" question:

Open the ‘Edit Scheme’ window and navigate to the Diagnostics tab. You’ll want to turn on “Enable Scribble” and “Malloc Stack”. ... in short, “Enabled Scribble” will cause the allocator to write 0xAA to newly allocated memory and write 0x55 to deallocated memory. “Malloc Stack” will log the allocation and free history of your memory.

If you've read this far, you'll probably be interested in Apple's Technical Notes:

• Technical Note TN2239 - iOS Debugging Magic
• Technical Note TN2124 - Mac OS X Debugging Magic