Learning that you can use unions in C for grouping things into namespaces

Re:Learning that you can use unions in C for grouping things... by formerly_proven on Sunday August 01, 2021 @05:19PM (#28030095)

Accessing packed struct members works fine on x86, but will blow up at runtime or do weird things on platforms which don't support unaligned loads or stores.

The correct way to access packed structs is through memcpy, just like you'd access any other potentially unaligned object.

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Re:Learning that you can use unions in C for grouping things... by 10000truths on Sunday August 01, 2021 @05:39PM (#28030284)

For architectures where unaligned accesses are illegal, gcc will generate multiple load/store instructions when accessing packed struct fields by name. The main caveat to look out for is taking the address of a packed struct member and then dereferencing it.

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Re:Learning that you can use unions in C for grouping things... by formerly_proven on Monday August 02, 2021 @02:49AM (#28033608)

Ah, right. Thanks for the correction.

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