Re: [boost] [interest] underlying type library

Subject: Re: [boost] [interest] underlying type library
From: Julian Gonggrijp (j.gonggrijp_at_[hidden])
Date: 2011-08-23 04:09:16

John Bytheway wrote:

> On 22/08/11 16:20, Julian Gonggrijp wrote:
>> [...] Could you quote the lines from the standard in 
>> which memcpy over non-PODs is deemed undefined, just in order for me 
>> to know the exact wording?
> 
> Well, I can't find it saying that explicitly; indeed there are hardly
> any mentions on memcpy in the standard at all, but here's a relevant bit
> for C++0x, from N3290 [basic.types] (3.9) p3:
> 
> For any trivially copyable type T, if two pointers to T point to
> distinct T objects obj1 and obj2, where neither obj1 nor obj2 is a
> base-class subobject, if the underlying bytes (1.7) making up obj1 are
> copied into obj2,41 obj2 shall subsequently hold the same value as obj1.
> [ Example:
> T* t1p;
> T* t2p;
> // provided that t2p points to an initialized object ...
> std::memcpy(t1p, t2p, sizeof(T));
> // at this point, every subobject of trivially copyable type in *t1p
> contains
> // the same value as the corresponding subobject in *t2p
> — end example ]

Interesting. Thank you.