From: "Berger, Daniel" <Daniel.Berger@...>
Date: 2005-09-14T06:38:44+09:00
Subject: Question on StringValuePtr, rb_str_dup

Hi all,

I'm having a hard time preserving a string.  Essentially, what's
happening is that even though I'm dup'ing the original string, after I
pass it a C function that modifies the receiver, both the original
string *and* the dup appear to be affected.

Here's a generic example of what I mean:

static VALUE foo(VALUE klass, VALUE rstring_orig){
   VALUE rstring;
   char* string;

   rstring = rb_str_dup(rstring_orig);
   string = StringValuePtr(rstring);

   c_func_that_modifies_receiver(string);

   return rb_str_new2(string);   
}

string = "hello"
foo(string)
p string # modified, but shouldn't be.

In other words, even though I've dup'd the original string and have sent
the dup to the C function that modifies the receiver, the original
string is still being modified.

What am I doing wrong here?

Thanks.

Dan