Adjacent comment pretty much explained it. Sometimes it's printf, sometimes it's subtle tweaks to program behavior in strategic places, sometimes it's adding as

Adjacent comment pretty much explained it. Sometimes it's printf, sometimes it's subtle tweaks to program behavior in strategic places, sometimes it's adding asserts (that might very well call functions not intended for public consumption). I always start debugging by coming up with a theory about why the observed behavior occurred. The fastest way to validate that is generally one or two tiny changes to the program. I only break out the debug tooling for the serious stuff that has me scratching my head in confusion. Either because the behavior has me thinking "there's no way that's possible" (spoiler: almost always memory corruption) or because I'm segfaulting in a shared library that I didn't compile or because I'm well into some obvious badlands with concurrency or memory corruption or the like.