While chasing a segfault around a complicated and grouchy c++ program I added several `//comments` and `cout` statements, but no 'actual' code. Then, suddenly, for no apparent reason the segfault vanishes.

I'm happy, but still a little worried, because I don't think I fixed anything and there was clearly something wrong. 

How can I debug a problem that has disappeared? (sadly I don't have a version that's still giving a segfault, any older versions have other problems)

As an aside, do you think I am mistaken in thinking that I have only added `//comments` and `cout` statements? Is it more likely that I accidentally altered something else?