Path: utzoo!utgpu!watserv1!watmath!att!att!linac!uwm.edu!zaphod.mps.ohio-state.edu!rpi!uupsi!sunic!nuug!sigyn.idt.unit.no!ugle.unit.no!hanche
From: hanche@imf.unit.no (Harald Hanche-Olsen)
Newsgroups: comp.sys.mac.programmer
Subject: Function pointers and lack of type conversion in Think C
Message-ID: <HANCHE.90Nov2180656@hufsa.imf.unit.no>
Date: 2 Nov 90 17:06:56 GMT
Sender: news@ugle.unit.no
Organization: The Norwegian Institute of Technology, Trondheim, Norway.
Lines: 38

Executive summary:  Bug in Think C -- If a function is called via a
function pointer then automatic type conversion of its args does not
take place.

Consider the following file:
----------------
typedef void (*funpoint)(long, long);
void fun_a(long,long);

main()
{
	funpoint fun;
	int i=1, j=2;
	fun=fun_a;
	(*fun)(i,j);
	fun_a(i,j);
}

void fun_a(long a, long b)
{
	printf("fun_a: %08lx %08lx\n", a, b);
}
----------------
This produces the two lines of output:

fun_a: 00010002 00020001   <<== WRONG  (int args are not converted to longs)
fun_a: 00000001 00000002   <<== Right

Think C has no excuse for this, as the fun pointer has a type that
allows the compiler to determine the type of the arguments.

This caused lots of interesting crashes for me, as I was porting a
U**x program that likes to play with function pointers.  Comments?

- Harald Hanche-Olsen <hanche@imf.unit.no>
  Division of Mathematical Sciences
  The Norwegian Institute of Technology
  N-7034 Trondheim, NORWAY