"how confidently can you say that there's no other instance of something like this slipping in? " Well, you have compilers that displays you warnings about it.

"how confidently can you say that there's no other instance of something like this slipping in? " Well, you have compilers that displays you warnings about it. If you don't catch the error you have static analyzers, if not you have Valgrind and other memory tools(linux have some jewels here), and if not you have your own parsing code for automatic checking of anything suspicious like becoming superuser. So is not that disturbing as this example is something that even gcc with Waring=all catch. LLVM is better in this respect.