Re: [xml] xmlReaderForIO

[Minor Gordon <gordon zib de>]

Daniel Veillard wrote:

> On Mon, May 03, 2004 at 04:18:08PM +0200, Minor Gordon wrote:
>  
>
> > Hello,
> >
> > I am trying to use xmlReaderForIO() to read from some custom buffer 
> > structures.  I couldn't find any examples of this in the documentation, 
> > so I'm winging it.
> >    
>
>  http://xmlsoft.org/examples/io1.c
>  gives a somewhat similar example even if it does not use that API.
>
>  
>
> > For the IO reader, I have:
> > xmlTextReaderPtr reader = 
> > xmlReaderForIO((xmlInputReadCallback)xmlReadBuffers,NULL,NULL,"sbns", 
> > NULL, 0);
> >
> > which I've tried in several variations (giving an encoding "utf-8", 
> > makin a dummy close callback, passing an object in ioctx, etc.).  This 
> > is the variation I want.
> >
> > The function xmlReadBuffers has the signature:
> > int xmlReadBuffers(void * context, char * buffer, int len)
> >
> > When the program hits the first line (reader = ) it jumps into nowhere.  
> > Not exactly nowhere -- access violation at 0x00000010.  Like it's trying 
> > to access an element of an array that's actually a NULL pointer.
> > I don't think it's an environment problem, because the file reader works 
> > (so the DLLs are loading).
> >
> > Is there something with the code?
> >    
>
>  Impossible to say without seeing the code. Make sure first 
> that the given example work in your environemnt then if yes,
> the best thing is to use a debugger to trace what's happening.
>  

Hello,

The problem turned out to be multi-threading.
I switched to the libxml2_a.lib and it worked..

I've looked at the I/O examples and header file.  The example you 
pointed out has this function:

static int
sqlRead(void * context, char * buffer, int len) {
  const char *ptr = (const char *) context;

  if ((context == NULL) || (buffer == NULL) || (len < 0))
      return(-1);

  if (len > rlen) len = rlen;
  memcpy(buffer, ptr, len);
  rlen -= len;
  return(len);
}


which looks good.
However,
I don't want to be given an allocated buffer to fill.  I already have 
the XML in memory, and I simply want to return a buffer and tell libxml2 
how long it is.  No copy.

Is that possible?  Surely someone else has done this..

Thank you for your help.

Minor