Evan Jones <evanj@xxxxxxx> writes: > 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)); It's safe w.r.t. aliasing rules, provided memcpy() implementation is safe, and chances are high that memcpy() is safe ;) > 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? AFAIK, there is no way to write through void pointer ;) You need to cast to something else before writing anyway. It's "[[un]signed] char *" that you can use to write to and read from anything. This is what makes it possible to implement memcpy() in C/C++. -- Sergei.
