Here you have a snippet: 
SV *
_smooth2( yp, wp, lambda_in, m )
         char * yp
         char * wp
         SV * lambda_in
         int m
   CODE:
{
  int i, i1, i2, ip;
  double c[MMAX+1], d[MMAX+1], e[MMAX+1],
        w[MMAX+1], y[MMAX+1], z[MMAX+1],
        lambda;
  double * ya;
  double * wa;
  ya = (double *) yp;
  wa = (double *) wp;

[download]
You see, the c uses pointers to address the strings. Char is the default type, you need to convert inside the code.

From perl, I call: 

 
Smooth::_smooth2( $py, $pw, $lambda, scalar( @$yref ) );

[download]
Where the $py and $pw are strings. XS automagically builds the pointers for you.

Hope this helps,

Jeroen
"We are not alone"(FZ)
Update: Because the c-code sees only the pointers, no copy is made. To be sure, I tested it with a fresh module: TestMemXS: 

#XS
#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"
#include "unistd.h"
 
MODULE = TestMemXS              PACKAGE = TestMemXS
 
 
void
_test( yp )
         char * yp
 
   CODE:
{
  double * ya;
 
  ya = (double *) yp;
 
  sleep( 1000 );
}
-------------------
#testMemXS.pm
....
sub testMem{
  my $str = "\000" x 50e6;
  _test( $str );
}
....
-------------------
perl -MTestMemXS -e 'testMem()'

[download]
The perl process didn't exceed 55M...

In reply to Re: Passing a very large string by reference to a c library by jeroenes
in thread Passing a very large string by reference to a c library by dino

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