Comment by salgernon

printf can/does have side effects. Perhaps one of the parameters to the call is obscured by a macro, which has some other effect. Or perhaps stdout was redirected and the printf was required to prevent line buffering from hanging a downstream consumer. The point is, if it seems very unlikely that such and such could cause a problem, it probably isnt the true cause. (Printf itself isn't the fix, it is just involved in the fix)