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0 pointsburfog7y ago0 comments

That part of the standard only covers the cast. It means that you won't mangle a pointer if you cast it to a void pointer and then back to the original pointer type.

Accessing the data that is being pointed at is another matter entirely. You must satisfy alignment constraints. You also must not read any memory as a type other than what it was written as, aside from a very limited exception for type char.

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garethrees7y ago

There doesn't seem to be any pointer dereference on the line that paavoova quoted, so I don't see how your comment applies.

burfogOP7y ago

The trouble is that it is very easy to interpret things the wrong way. You showed that the casting is OK. People will tend to wrongly assume that they are home free at that point, and everything will be standards-compliant. Most people don't realize that the dereference itself can be a problem. Casting is very frequently followed by non-compliant dereferences. The gcc warnings about strict aliasing do not catch all the problems. Adding more casts, including one to a void pointer, is a common way to make warnings go away without actually stopping the compiler from breaking non-compliant code.

Looking at the full code on the web site, I think it is compliant but dangerous. It is decently likely to trigger gcc bugs.

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