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Re: strict aliasing: how to swap pointers
Andrew Haley wrote:
so, this:
int *sp = &int_var;
void *vp = sp;
*(short*)vp = 22;
is undefined behaviour, and may well not do what you want.
Ignoring platform specific issues like byte order and size, is it safe
to use memcpy instead? Example:
int *sp = &int_var;
void *vp = sp;
short value = 22;
memcpy(vp, &value, sizeof(value));
In my experiments with strict aliasing and GCC, replacing accesses like
this with memcpy resolves the problem, even when GCC inlines the memcpy
into a simple load/store. It seems to me that this should be okay, since
the write through a void pointer is permitted to alias anything?
Or is the only safe way to use the mayalias attribute?
I think I'm starting to understand why many people insist on using
-fno-strict-aliasing.
Evan
--
Evan Jones
http://evanjones.ca/