When calling a C function from Perl, for example using Inline::C:
use feature qw(say);
use strict;
use warnings;
use Inline C => './test.c';
say "Calling test()..";
test();
say "Finished.";
where test.c is:
void test()
{
SV *sv_variable = newSVpv("test", 0);
// do something..
//SvREFCNT_dec(sv_variable); // free variable
printf( "Returning from test()..\n");
return;
}
The script seems to work fine whether I call SvREFCNT_dec(sv_variable) or not. According to perlguts:
To free an SV that you've created, call SvREFCNT_dec(SV*). Normally this call is not necessary
Yes, you should decrement the refcount. (If you don't, there are no immediate bad effects, but you've created a memory leak.)
perlguts probably says this normally isn't necessary because most SVs aren't just used internally in C functions; they're part of structures reachable from Perl space or put on the stack.
But note that your code structure isn't exception safe: If any function in // do something throws, sv_variable will leak (because SvREFCNT_dec is never reached). This can be fixed by doing:
SV *sv_variable = sv_2mortal(newSVpv("test", 0));
sv_2mortal is like a deferred SvREFCNT_dec: It will decrement the reference count some time "later".
(If you're creating an SV from a string literal, newSVpvs("test") is better than newSVpv because it doesn't have to compute the length at runtime.)