Re: [xml] memory tag error occurs

[ecforu <ecforusers gmail com>]

I am still confused because I think that I am using xmlChar * that are causing the problem.  See my code below.  Using gdb the error shows up on the calls to 
      xmlMemFree(xmlElementName);
      xmlMemFree(xpathExpr);

Those 2 strings I am freeing with xmlMemFree come from a xmlStrncatNew and a xmlStrndup.  I was under the impression that these created new strings with xmlMalloc which I should be able to xmlMemFree... No?

Thanks

----- CODE CAUSING PROBLEM -----
GetElements(xmlNodePtr node, const char * elementName)
{
   XmlElementListPtr elements = NULL;
   xmlXPathContextPtr xpathCtx;
   xmlXPathObjectPtr xpathObj;
   int status = 0;

   if (node != NULL)
   {
      /* Create xpath evaluation context */
      xpathCtx = xmlXPathNewContext(node->doc);
      if (xpathCtx == NULL)
      {
         fprintf(stderr, "Error: unable to create new XPath context\n");
         status = -1;
      }

      xpathCtx->node = node;

      const xmlChar * xPathLocal = (xmlChar *)"./";
      xmlChar * xmlElementName = xmlCharStrndup(elementName, strlen(elementName));
      xmlChar * xpathExpr = xmlStrncatNew(xPathLocal, xmlElementName, -1);

      /* Evaluate xpath _expression_ */
      xpathObj = xmlXPathEvalExpression(xpathExpr, xpathCtx);
      if (xpathObj == NULL)
      {
         fprintf(stderr, "Error: unable to evaluate xpath _expression_ \"%s\"\n",
               xpathExpr);
      }

      /* Print results */
      elements = BuildElementList(xpathObj);

      /* Cleanup */
      xmlMemFree(xmlElementName);
      xmlMemFree(xpathExpr);
      xmlXPathFreeObject(xpathObj);
      xmlXPathFreeContext(xpathCtx);
   }

   return elements;
}

On Thu, Apr 29, 2010 at 9:14 AM, Daniel Veillard <veillard redhat com> wrote:

On Wed, Apr 28, 2010 at 11:01:25AM -0400, ecforu wrote:
> I keep getting the same errors (see below) when I run my c program using
> libxml2-2.7.3.

 means 1/ you're using a libxml2 library build with memory debugging
 2/ you're doing allocation errors in your program

> xmlMallocBreakpoint reached on block 0
> Memory tag error occurs :0x35988
>      bye
> xmlMemFree(359A0) error
> xmlMallocBreakpoint reached on block 0

 run your program under gdb and put a breakpoint in xmlMallocBreakpoint
to stop the programe at the time teh error is made and debug.

 Note that compiling with memory debug means that you will see such an
error if you allocate with malloc and try to xmlFree() the result or
try to free() memory allocated by libxml2 (instead of using xmlFree)
which usually work but not under memory debug which is specifically
designed to catch libxml2 memeory usage errors.

Daniel

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