Updated: When to "mortalize" a variable in Perl Inline::C
I am trying to wrap a C library into Perl. I have tinkered with XS
but being unsuccessful I thought I should start simply with Inline::C
. My question is on Mortalization. I have been reading perlguts as best as I am able, but am still confused. Do I need to call sv_2mortal
on an SV* that is to be returned if I am not pushing it onto the stack?
(PS I really am working on a less than functional knowledge of C which is hurting me. I have a friend who knows C helping me, but he doesn't know any Perl).
I am providing a sample below. The function FLIGetLibVersion
simply puts len
characters of the library version onto char* ver
. My question is will the version_return
form of my C code leak memory?
N.B. any other comments on this code is welcomed.
#!/usr/bin/perl
use strict;
use warnings;
use 5.10.1;
use Inline (
C => 'DATA',
LIBS => '-lm -lfli',
FORCE_BUILD => 1,
);
say version_stack();
say version_return();
__DATA__
__C__
#include <stdio.h>
#include "libfli.h"
void version_stack() {
Inline_Stack_Vars;
Inline_Stack_Reset;
size_t len = 50;
char ver[len];
FLIGetLibVersion(ver, len);
Inline_Stack_Push(sv_2mortal(newSVpv(ver,strlen(ver))));
Inline_Stack_Done;
}
SV* version_return() {
size_t len = 50;
char ver[len];
FLIGetLibVersion(ver, len);
SV* ret = newSVpv(ver, strlen(ver));
return ret;
}
Edit:
In an attempt to answer this myself, I tried changing the line to
SV* ret = sv_2mortal(newSVpv(ver, strlen(ver)));
and now when I run the script I get the same output that I did previously plus an extra warning. Here is the output:
Software Development Library for Linux 1.99
Software Development Library for Linux 1.99
Att开发者_开发知识库empt to free unreferenced scalar: SV 0x2308aa8, Perl interpreter: 0x22cb010.
I imagine that this means that I don't need to mortalize in this case? I suspect that the error is saying that I marked for collection something that was already in line for collection. Can someone confirm for me that that is what that warning means?
I've been maintaining Set::Object for many years and had this question, too - perhaps best to look at the source of that code to see when stuff should be mortalised (github.com/samv/Set-Object). I know Set::Object has it right after many changes. I think though, it's whenever you're pushing the SV onto the return stack. Not sure how Inline changes all that.
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