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When reading from a binary source, I've seen that, instead of unions, the char pointer will be cast to a pointer to the appropriate data structure. What is the
by MereInterest 11y ago
When reading from a binary source, I've seen that, instead of unions, the char pointer will be cast to a pointer to the appropriate data structure. What is the advantage of using a union instead of casting?
- theseoafs 11y agoWell, for one, unions have defined behavior in C, while passing pointers around and casting them randomly doesn't. I don't know if this is the best example. Generally you see unions in C to cover "tagged unions", I.e. Those things that would be subsumed by algebraic data types in other languages.
- MereInterest 11y agoAh, got it. I am used to C++, where accessing the non-active member of the union is undefined behavior. Thank you.
- stephencanon 11y agoThe usual way to do this via memcpy, rather than either a union (requires some non-portable extension like "packed") or pointer casting (invokes undefined behavior if alignment isn't satisfied).