unusual behaviour with gdb

[dinesh999lama]

When i use the step command in gdb instead of going forwared it jumps to different lines in gdb while debugging c++ code. i'm using cmake to build the code.

[coder777]

You probably use the release version for your debugging. Make sure that you use the debug version.

[Repeater]

To add to coder777's words, if you're building with optimisations turned on, then various lines of your source code will be re-ordered, maybe eliminated entirely, replaced with something simpler, and a host of other things that optimisers do to make your code faster. So when you step to the next instruction, maybe that instruction actually corresponds to a line that was earlier in your source code. Or five lines later.

Typically, a debug version will have those optimisation turned off (or at least, turned down a lot) so that your source code more closely matches the generated executable.

But wait! You are now thinking "But doesn't that mean that there could be a bug in my release version, with all the optimisations turned on, that doesn't exist in the debug version?" Yes, it does mean that. "So how can I debug a bug that vanishes when I try to look at it?" How indeed.... :)

[dutch]

So the upshot is to compile with -O0 -g (no optimizations, include debug information)