The Lost Art of C Structure Packing

I do optimal structure (and bit) packing without much thought because it is an old habit. As the article states, I have noticed that the only other people that do habitual careful structure optimization these days have been doing low-level and high-performance code as long as I have. Most programmers are oblivious to it. The reasons you would do it today are different than a decade ago and the rules have changed because the processors have changed. To add two…

Awareness of the layout and size of data is still very common in game development. Mike Acton did a great talk related to this at CppCon a few years ago : https://www.youtube.com/watch?v=rX0ItVEVjHc

TL;DR: to get smaller structures, don't do stuff like this: struct foo { char a; int b; char c; int d; }; but this: struct foo { int b; // or int b, c; int c; char a; char c; }; Basically if you sort the types by size in reverse descending order, you get optimal packing without messing with compiler-specific packing extensions that skew alignment and possibly bloat code. The worst that you will get is padding at the…

If you do any development that requires touching Win32, structure packing and memory alignment is still very real. I was recently doing that in the context of improving a language’s library support for something that had to go through the OS SDK. I don’t miss the days when that stuff was the norm.