Re:Stop Memsetting Structures
by saagarjha on Saturday April 27, 2019 @10:57PM
(#19769030)
I feel like accessing the bytes that correspond to padding might be implementation-defined, but I couldn't find this in the standard.
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Parent comment was edited to include this quote:
_6 When a value is stored in an object of structure or union type, including in a member object, the bytes of the object representation that correspond to any padding bytes take unspecified values. 51)_
So sure, a memcpy after a memset aught to preserve all the bytes, but if they are updated through a struct which contains padding then the values in the padding bytes will be left unspecified.
I don't think it is. It wouldn't make sense since memcpy is basically supposed to convert between arbitrary binary data.
From a practical point of view, yes, but I would be very surprised if the C standard had any accommodation for memcpy being a way to leak the value of a structure's padding.
You clearly haven't understood the thread.