Godbolt's Second Law

Hot on the heels of Godbolt’s first law comes (fanfare please!) Godbolt’s Second Law!


Godbolt’s Second Law — If a piece of code compiles, links, runs and appears to work first time, then it is almost certainly flawed in some subtle and hard-to-find way!


Yet another amazing revelation, don’t you think? On a more serious note I honestly have found this to be true. Writing code is a really tricky thing to do. Even for the most trivial piece of code, one can’t help but make errors. Usually these errors are caught by the compiler — if they’re simple typos — or the linker — if you’ve forgotten to include the right libraries — or by an obvious crash at runtime for almost everything else.

But when it all works the first time, then alarm bells should start ringing! “It really can’t be that easy, surely?” you should be asking yourself! Whenever this has happened to me, I’ve almost certainly missed out some amazingly important boundary condition case.

Usually it’s some memory leak, or a threading issue. Something that clearly wasn’t taken into account at all when bashing out the original code. If I had taken these more difficult programming issues into account, then no doubt I’d’ve made some typos or else some completely daft errors. So therein lies the heart of my second law.

Does anyone else out there have any pet theories on this? Or indeed am I alone in being highly suspicious of code that appears to work first time?

Filed under: Coding
Posted at 21:16:00 GMT on 6th February 2006.

About Matt Godbolt

Matt Godbolt is a C++ developer working in Chicago in the finance industry.