TITLE: Casting to and from void pointers


PROBLEM: joey@tessi.com (Joey Pruett)

... the c++ ref manual (2nd ed) and sure enough, there it was on
page 490, section r.4.6:

"A pointer to function may be converted to a void * provided a
void * has sufficient bits to hold it."

i don't have the arm handy, so i don't know if there is a rationale
for this.  or maybe this has been addressed by the standards body.


RESPONSE: steve@taumet.com (Steve Clamage), 2 May 93

This is a hardware issue.  Some machines use function pointers which
are larger than data pointers, quite apart from memory model issues.
(See the C FAQ for more discussion.)

The rule in C and in C++ is therefore that you cannot depend on being
able to convert a function pointer to void* and back again.  The
alternative would be to disallow the use of C or C++ on some machines.

[ But you ARE allowed to convert a pointer to an object to and from
  a void pointer. Note this does NOT mean casting to void pointer then
  to some other class pointer is valid. -adc ]