I still use a lot of printfs, but I make heavy use of the debugger. In general, my strategy for difficult bugs is to find a point A where you know the code is w

I still use a lot of printfs, but I make heavy use of the debugger. In general, my strategy for difficult bugs is to find a point A where you know the code is working correctly, find point B where you know it's broken and can catch it in the debugger or log, and step forwards from A and backwards from B until you find the bug in the middle. When debugging difficult, intermittent problems (e.g. non-repro crashes) my strategy is to keep a log of when it occurs, add lots of diagnostics and asserts around where I think the problem is, until hopefully I can catch it in the debugger or notice a pattern. 90% of the work of debugging is creating a quickly reproducible test case. Once you have that you can usually solve it.