(no subject)

Hi,
first of all I apologize in advance if the problems I
encountered has already been discussed here.

1 .I have a problem when I try to work with
C-structures using SWIG-wrapped C-functions in Perl. 

In a nutshell, why it makes a difference if I call:

# prints actual content of the structure
SwigTest::print_string("$Cstruct::cstruct->{key}");

or 

# prints nothing!
SwigTest::print_string($Cstruct::cstruct->{key});

In the latter case a null(!) pointer is passed to the
function. The function prototype is

void print_string(const char * str);

and the struct is defined as

typedef struct cstruct {
    char *key;
} cstruct_t;

The argument passed to the function will be cast in
char * pointer. So, whatever it is, it will not be
zero after casting. But if it is zero, how comes that
"quoting" the argument converts it to a nonempty
string ?

If instead of C-structure a Perl hash  is used, there
problem disappear.

Environment: 
        SunOS 5.8 Generic_117000-01 sun4u sparc,
        perl v5.8.5 built for sun4-solaris,
        SWIG Version 1.3.22. Compiled with g++
[sparc-sun-solaris2.8],
        gcc version 3.4.1.

To run the example:

swig -perl -shadow SwigTest.i;

gcc -D_GNU_SOURCE -g -fPIC -mtune=ultrasparc -O3
-I/usr/gnu/install/perl-5.8.5/lib/5.8.5/sun4-sol
aris/CORE -c SwigTest_wrap.c SwigTest.c;

ld -G SwigTest.o SwigTest_wrap.o -o SwigTest.so;

./Swigtest.pl;

You will have to adjust the path to perl executable
and  to perl CORE directory.

Here is the full source:

//--------------SwigTest.c--------------//
#include <stdio.h>
#include "SwigTest.h"

void print_string(const char * str)
{
    if(0==str)
        printf("ZERO POINTER!\n", str);
    else if(0==*str)
        printf("Empty string!\n", str);
    else
        printf("%s\n", str);
}

cstruct_t *cstruct_make()
{
    cstruct_t *cstruct;

    cstruct=(cstruct_t *)malloc(sizeof(cstruct_t));

    return(cstruct);
}
//--------------------------------------//

//--------------SwigTest.h--------------//
typedef struct cstruct {
    char *key;
} cstruct_t;

void print_string(const char * str);
cstruct_t * cstruct_make();
//--------------------------------------//

//--------------SwigTest.i--------------//
%module SwigTest

%{
#include <stdio.h>
#include "SwigTest.h"
%}

typedef struct cstruct {
    char *key;
} cstruct_t;


%name(print_string) extern void print_string(const
char *str);
%name(cstruct_make) extern cstruct_t *
cstruct_make(void);
//--------------------------------------//

//--------------Cstruct.pm--------------//
package Cstruct;

use strict;
use SwigTest;

use vars qw($hr $cstruct);

# This package provides access to two variables
# One is an ordinary perl hash, with one element
# The other is a hash tied via SWIG to a C structure
containing one element

my %hash;
$hr =\%hash;
print "$hr\n";
$hr->{key} = "Contents of hash element with key
\"key\"";

$cstruct=SwigTest::cstruct_make() or die;
$cstruct->{key}="Contents of hash element linked via
Swig to C structure element";


print "[Loaded: ", __FILE__, "]\n";
1;
//--------------------------------------//

//-----------Swigtest.pl----------------//
#!/usr/gnu/bin/perl -w

use strict;
use lib (".");

use Cstruct;
use SwigTest;

print "\n\n";

print "\$Cstruct::hr is a                    
$Cstruct::hr\n";
print "\$Cstruct::cstruct is a               
$Cstruct::cstruct\n";

print "\n";

print "\$Cstruct::hr->{key} contains:       ";
print $Cstruct::hr->{key},"\n";
print "\$Cstruct::cstrcut->{key} contains:  ";
print $Cstruct::cstruct->{key},"\n";

print "\n";

print "When  \$Cstruct::hr->{key}       is passed to C
it contains: ";
SwigTest::print_string($Cstruct::hr->{key});

print "When  \$Cstruct::cstruct->{key}  is passed to C
it contains: ";
SwigTest::print_string($Cstruct::cstruct->{key});

print "When \"\$Cstruct::cstruct->{key}\" is passed to
C it contains: ";
SwigTest::print_string("$Cstruct::cstruct->{key}");

print "\n";
//--------------------------------------//

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