Void function pointers

[Larry Jones]

In article <1991Jan24.181041.4894 at Think.COM>, barmar at think.com (Barry Margolin) writes:
> In article <SARROYO.91Jan24120512 at govtdev-11w9.shearson.com> sarroyo at govtdev-11w9.shearson.com (Suzanne Arroyo) writes:
> [Regarding passing an int(*)() to a function expecting a void(*)()]
> >this works, but is messy:
> >	foo ( 7, 3.131592653938789, (void(*)(int, double) )bar);
> 
> Is this actually guaranteed to work right?  What if the implementation uses
> a different calling sequence for a function returning void from one
> returning int?  For instance, the space for a return value might be
> allocated by the caller.  Is this allowed (I know they are allowed to use
> different calling sequences for varargs functions, but is the return type
> also allowed to influence the calling sequence)?  If so, then foo won't
> call bar properly.

No, it's not guaranteed to work right.  It will work on many architectures
for many return types, but not all.  Structure return types are the most
likely candidates for misbehavior because the space for a returned structure
is frequently allocated by the caller and the address passed as an additional
argument, so the call does not work.  It is not possible to call a mis-
declared function with predictable results -- casting to the correct type may
shut up the compiler, but it won't make it right.
----
Larry Jones, SDRC, 2000 Eastman Dr., Milford, OH  45150-2789  513-576-2070
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