in reply to Re: Passing undef to XSUB
in thread Passing undef to XSUB

Would int* also work? Like in 
int
foo(ap,bp)
    int* ap
    int* bp
    PREINIT:
      int a, b;
    CODE:
      a = ap ? *ap : -1;
      b = bp ? *bp : -1;
      RETVAL = a * b;
    OUTPUT:
      RETVAL

[download]

Replies are listed 'Best First'.
Re^3: Passing undef to XSUB
by syphilis (Archbishop) on May 08, 2008 at 00:49 UTC
    Would int* also work?

    No, but int would: 
    int
foo(ap,bp)
    int ap
    int bp
    PREINIT:
      int a, b;
    CODE:
      a = ap ? ap : -1;
      b = bp ? bp : -1;
      RETVAL = a * b;
    OUTPUT:
      RETVAL

    [download]
    Though, if warnings are enabled, that produces a "Use of uninitialized value in subroutine entry..." for each undef that's passed to it - no such warning with educated_foo's rendition.

    Cheers,
    Rob
[reply]
[d/l]
[select]
      It (presumably) compiles and runs, but I wouldn't say it works. Not only does it introduce a warning, it gives incorrect results for arguments equal to zero.
[reply]
        it gives incorrect results for arguments equal to zero

        Yes ... I had missed the important point that 0 ought to be evaluated as 0 (and not -1).

        Now I understand what your speculative code was driving at.

        Cheers,
        Rob
[reply]

      I don't know much about XS, but I wonder if this code is able to distinguish between when it's passed undef and when it's passed 0. That is, can it see the difference between foo( undef, undef ) and foo( 0, 0 )? It seems to me the "uninitialized value" warning is undef getting turned into 0.

[reply]
[d/l]
[select]
        It seems to me the "uninitialized value" warning is undef getting turned into 0

        Yes, I think that's right: 
        use warnings;

use Inline C => Config =>
    BUILD_NOISY => 1;

use Inline C => <<'EOC';

void foo(int a) {}

void bar(SV * a) {}

void baz(SV * a) {
     int i = (int)SvIV(a);
}
    
EOC

$u = undef;

foo($u); # warning
bar($u); # no warning
baz($u); # warning

        [download]
        Cheers,
        Rob
[reply]
[d/l]
Re^3: Passing undef to XSUB
by educated_foo (Vicar) on May 07, 2008 at 23:29 UTC
    Not for me -- int* doesn't appear to have a typemap for me (perl 5.8.8).
[reply]
      Thanks
[reply]

In Section Seekers of Perl Wisdom