On Sun, Mar 29, 2015 at 3:26 PM, Andreas Schwab <[email protected]> wrote:
> Godmar Back <[email protected]> writes:
>
>> ps: I would like to see the warning, of course, since casting a bool
>> returning function to an int returning function is undefined behavior.
>
> The cast itself is ok, the undefined behavior only occurs when calling
> it without casting back.
>
Thanks. I'm a bit confused then what constitutes defined & undefined behavior.
The actual situation I encountered is best described by this example:
--
/* Tested with gcc 4.4.7 and 4.8.2 -m32 */
#include <stdio.h>
#include <stdbool.h>
bool boolFunctionThatReturnsFalse() {
// I'm faking this here, but a real 'bool' function could
// place 0x100 in $eax when meaning to return false.
register bool r asm("%eax");
asm("mov $0x100, %eax");
return r;
}
typedef int (*intFunction)(void);
int
main()
{
if ( boolFunctionThatReturnsFalse() )
printf("true\n");
else
printf("false\n");
intFunction f = (intFunction) boolFunctionThatReturnsFalse;
if ( f() )
printf("true\n");
else
printf("false\n");
}
--
(I'm faking the return value of boolFunctionThatReturnsFalse here, but
I have observed this behavior in actual code.)
Is this defined or undefined behavior that my problem invokes?
- Godmar
