#pragma pack effect

Question

I was wondering if someone could explain to me what the #pragma pack preprocessor statement does, and more importantly, why one would want to use it.

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Answer 1

You'd likely only want to use this if you were coding to some hardware (e.g. a memory mapped device) which had strict requirements for register ordering and alignment.

However, this looks like a pretty blunt tool to achieve that end. A better approach would be to code a mini-driver in assembler and give it a C calling interface rather than fumbling around with this pragma.