Re: How get PV address?

[dave_the_m]

In XS code, SvPVX(sv) is correct if you're sure that sv is a valid PV value; otherwise one of the SvPV() or SvPV_force() functions/macros would be more appropriate. You're seeing a truncated version of the SvPVX() value because you're coercing it to an integer. You should be returning a suitable pointer type instead, or using an integer type like UV, which is large enough to hold a pointer.

Dave.

[xiaoyafeng]

I use SvPVX is for test， since I know PV is hello world.:) The issue is I checked typemap,,in there,unsigned int int will convert to T_UV, so I don't think UV could hold this PV address. But If I change return type to char*, typemap will convert it to SV by sv_setpv.

[dave_the_m]

Well it all depends on what you want to do with the address. Are you passing it back to perl? Should perl see it as a (suitably large) integer value - i.e. the XS code returns an SVIV? What will perl do with the address?

Dave.

[xiaoyafeng]

Thanks, I set return type to UV, it works and I can call it back and forth in C:

use strict;
use warnings;
use Devel::Peek;

my $dd = "hello world\n";
Dump $dd;
my $ee = cc($dd);
printf("the dd string address is %x \n", cc($dd));
dd($ee);
use Inline Config => BUILD_NOISY => 1,
                                       CLEAN_AFTER_BUILD => 0;
use Inline 'C' => <<'CODE';

int dd(UV x){

                printf("string is %s \n", (char*)x);
                return 0;
}
UV cc(SV* a){
return SvPVX(a);
}
CODE
###############output###########
andy@andyhome:~/one-off$ perl abe.pl
SV = PV(0x56386170b050) at 0x56386172f008
  REFCNT = 1
  FLAGS = (POK,IsCOW,pPOK)
  PV = 0x5638617addf0 "hello world\n"\0
  CUR = 12
  LEN = 14
  COW_REFCNT = 1
the dd string address is 5638617addf0
string is hello world

I pass it back to perl, But I got little confused: in typemap, both unsigned int and UV refer to T_UV and in OUTPUT it does convert to UV:

int             T_IV
unsigned        T_UV
unsigned int    T_UV
UV              T_UV
T_UV
     sv_setuv($arg, (UV)$var);

why seems perl neglect typemap file but use config?

Platform:
    osname=linux
    osvers=4.15.0-52-generic
    archname=x86_64-linux
    uname='linux andyhome 4.15.0-52-generic #56-ubuntu smp tue jun 4 2
+2:49:08 utc 2019 x86_64 x86_64 x86_64 gnulinux '
    config_args='-de -Dprefix=/home/andy/perl5/perlbrew/perls/perl-5.3
+0.0 -Aeval:scriptdir=/home/andy/perl5/perlbrew/perls/perl-5.30.0/bin'
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=undef
    usemultiplicity=undef
    use64bitint=define
    use64bitall=define
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
    bincompat5005=undef
  Compiler:
    cc='cc'
    ccflags ='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-str
+ong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64'
    optimize='-O2'
    cppflags='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-str
+ong -I/usr/local/include'
    ccversion=''
    gccversion='7.4.0'
    gccosandvers=''
    intsize=4
    longsize=8
    ptrsize=8
    doublesize=8
    byteorder=12345678

Please enlighten me.