zero size structs with extern (C) attribute #3093
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| $(P Structs with no fields of non-zero size (aka $(I Empty Structs)) have a size of one byte.) | ||
| $(P A struct with no fields of non-zero size is an $(I Empty Struct). | ||
| An Empty Struct with a $(DDSUBLINK spec/attribute, linkage, Linkage Attribute) of `extern (C)` has a size of zero. | ||
| Otherwise, its size is one byte.) |
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This is wrong. I think you wanted to say that empty extern (C) struct size is the same as with the underlying C compiler. Also you might want to add what happens if the C compiler simply disallows empty structs?
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C11 6.7.2.1-8 says "If the struct-declaration-list does not contain any named members, either directly or via an anonymous structure or anonymous union, the behavior is undefined."
Undefined behavior is not disallowed.
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If we encounter a C compiler with different behavior, we'll adjust the spec.
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From what I recall, the problem being that gcc and clang don't agree with each other on the same platform. So you could choose to imitate gcc on Linux, but then you're abi incompatible with clang on Linux - which someone might instead choose to use.
But that's all by the by.
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Undefined behavior is not disallowed.
The point is, undefined behaviour allows refusal to compile. A reasonable C compiler could emit an error when encountering an empty struct.
If we encounter a C compiler with different behavior, we'll adjust the spec.
Better, but why not do it right away?
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ping @WalterBright |
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Clear up documentation to correspond with dlang/dmd#13009