> ryao 7 hours ago | parent | context | flag | on: Hacktical C: practical hacker's guide to the C pro...

  cast a `struct Foo*` into a `struct Bar*` and access the Foo through it (in practice we teach this as the "strict aliasing" rules, and that's how all(?) compilers implement it, but that's not what §6.5 paragraph 7 of the standard says!)

Use the union type. Abusing it for aliasing violates the standard too, but GCC and Clang implement an extension that permits this. Alternatively, just allocate a char array and cast it as you please. Strict aliasing does not apply to char arrays if I recall.

  allow a signed integer to overflow

Is this still true? I thought that the reason for this is because C left the implementation to define how signed arithmetic worked, meaning you could not assume two’s complement, but the most recent C standard was supposed to mandate two’s complement.

>> pass a NULL pointer to memcpy, even if the length is zero

> There is a reason for this. memcpy is allowed to start reading early as a performance optimization, before it does a branch that checks if reading is only.

Where did you get this idea from? It's not possible, since you can hand an address at the end of an array, and length 0. The array ends at the end of a page.

You can't read extra bytes in this case!