Re: Out-of-bounds nonsense

On Thu, 2 Nov 2006 18:32:21 UTC, Frederick Gotham <fgothamNO@xxxxxxxx>
wrote:

Roberto Waltman:

Not so:

/* in a system where sizeof long is 4 */
long obj1;
char obj2;
/* UB: attempts to copy 3 chars past obj2 */
memcpy(&obj1,&obj2,sizeof obj1);


Of course, you're right.

Type1 obj1;
Type2 obj2;

if (sizeof obj2 >= sizeof obj1)
memcpy(&obj1,&obj2,sizeof obj1);

May result in udefined behavior when Type1 != Type2 as the
representation of different types does not require that they are have
to have the same padding bits adn/or alignment requirements. memcpy
can fail in the lands of udefined behavior here. Accessing obje1
thereafter can end in anything but may not do what you thinks it
should do.

--
Tschau/Bye
Herbert

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Relevant Pages

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    ... Herbert Rosenau: ... representation of different types does not require that they are have ... to have the same padding bits adn/or alignment requirements. ...
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