this post was submitted on 22 Jul 2025
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Structs with union members that allow the same place in memory to be accessed either word-wise, byte-wise, or even bit-wise are a god-sent for everyone who needs to access IO-spaces, and I'm happy my C-compiler lets me do it.
#pragma push
Context?
You use it to "pack" bitfields, bytes etc together in structs/classes (wo functions), otherwise the computer usually align every variable on a 32bit boundary for speed.
You don't need that pragma to pack bitfields.
With say a 3bit int, then a 2bit int and various char, int etc and so on you did have to use the pragma with gcc & visual around 2012 at least
OK, I use the Keil ARM compiler, and never needed to push anything.
Then I'd make a unit test, there is no requirement to do so by the compiler (not even the order).