As a follow up to Efficient walk/iterate along a string, I started playing with an inline C callback iterator. The following works even with the commented out lines and doesn't appear to leak at all.

However, when I tried to run it as part of a benchmark, it crashes.

So, ignoring the absence of error checking, my questions are:

• Why does it crash in a Benchmark?
• How can it be improved?
• Are there any documentation or examples of using LvTARG macros to do the aliasing?
• Is there any documentation of the MULTICALL macros used by List::Util::reduce()?

  eg, where does multicall.h come from?

• How can I apply a (&$) prototype to strIter()?

#! perl -sw
use strict;
use Inline C => Config => BUILD_NOISY => 1;
use Inline C => <<'END_C',  NAME => 'strIter', CLEAN_AFTER_BUILD => 0;

void strIter( SV *code, SV *string )  {
    dSP;
    STRLEN i ;
    char *p = SvPVX( string );
    SV *c;

//    ENTER;
//    SAVETMPS;

    c = newSV( 1 );
    SvCUR( c ) = 1;
    SvLEN( c ) = 2;
    SvPVX( c ) = p;
    SvPOK_only( c );
    GvSV(PL_defgv) = c;

    for( i=0; i < SvCUR( string ); ++i ) {

        PUSHMARK(SP);
        call_sv( code, G_NOARGS |G_VOID );
        PUTBACK;
        SvPVX( c ) = ++p;
        SvPOK_only( c );

    }
//    FREETMPS;
//    LEAVE;
    GvSV(PL_defgv) = string;
}

END_C

use strict;
use Time::HiRes qw[ time ];
use Benchmark qw[ cmpthese ];

our $string = 'abcdefghijklmnopqrstuvwyxABCDEFGHIJKLMNOPQRSTUVWXY' x 1
+00;

for (1 .. 100 ) {
    strIter sub{ print; }, $string;
}
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