Hi,

As revealed in this demo by Devel::Peek::Dump(), calling foo($sv) can make significant alterations to the internals of $sv: 
use strict;
use warnings;
use Devel::Peek;


use Inline C =><<'EOC';

void foo(SV * sv) {
  printf("\n%s\n\n", SvPV_nolen(sv));
/*
  SvPOK_off(sv);
  SvPV_set(sv, NULL);
*/
}

EOC

my $sv = 12345;

Dump $sv;
foo($sv);
Dump($sv);

__END__

Outputs:

SV = IV(0x4ecd70) at 0x4ecd80
  REFCNT = 1
  FLAGS = (IOK,pIOK)
  IV = 12345

12345

SV = PVIV(0x4f0088) at 0x4ecd80
  REFCNT = 1
  FLAGS = (IOK,POK,pIOK,pPOK)
  IV = 12345
  PV = 0x25a4448 "12345"\0
  CUR = 5
  LEN = 10

[download]
Inside that XS sub foo() is there a simple way that, having called SVPV_nolen(), the internals of the provided argument can be restored to the states they held just prior to the calling of foo($sv) ?

Inclusion of the commented-out C-code in foo() goes some way to doing that ... but not all the way.
It will change the second Dump() to: 
SV = PVIV(0x4f0088) at 0x4ecd80
  REFCNT = 1
  FLAGS = (IOK,pIOK)
  IV = 12345
  PV = 0

[download]
That looks about right except that the SV is still PVIV, and the PV slot, although cleared, is still being displayed. Perhaps the PV slot is being displayed simply because the SV is PVIV, and the solution lies in getting the "PVIV" to revert to "IV".

Cheers,
Rob

In reply to Reverting the internals of an IV to their original states by syphilis

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