I written a wrapper around xmlXPathNewContext and xmlXPathEvalExpression
(maybe re-inventing the wheel :) ) to obtain an xmlXPathObjectPtr.
Here below there is the function:
/**
*
=====================================================================================
*@fn xmlXPathObjectPtr get_xml_elements(xmlNodePtr nodePtr,char
*elementName)
* @brief this function looks for elements named elementName in the
* passed xmlNodePtr.
* @param nodePtr a xmlNodePtr where to look for element named
* elementName
* @param context an xmlXPathContextPtr passed in case of recursive
* parsing and recusive use of get_xml_elements
* @return xmlXPathObjectPtr containing one or more element named
* elementName. NOTE: Returned pointer must be freed by the caller
with
* xmlXPathFreeObject()
*
=====================================================================================
*/
xmlXPathObjectPtr get_xml_elements(xmlNodePtr nodePtr,char *elementName)
{
xmlXPathObjectPtr result=NULL;
xmlChar * lookup=NULL;
int extraSpace=strlen("child::");
xmlXPathContextPtr context=NULL;
/** check parameters */
if(nodePtr==NULL || elementName == NULL){
ERRORS(EINVAL,"null pointer param
passed\nnodePtr=%p,elementName=%p",nodePtr,elementName);
return NULL;
}
/** xmlXPathNewContext allocs a xmlXPathContextPtr */
context = xmlXPathNewContext(nodePtr->doc);
if(context==NULL){
ERRORS(ENOMEM,"xmlXPathNewContext fails\n");
return NULL;
}
/** configure node, the current node, to the one passed in the arg */
context->node=nodePtr;
/** resize lookup of extraspace+1 :1 for \0 and extraspace for axis */
lookup=calloc(strlen(elementName)+extraSpace+1,sizeof(xmlChar));
if(lookup==NULL){
ERRORS(ENOMEM,"Error allocating space for alloc new string
child::%s\n",elementName);
return NULL;
}
strcat((char *)lookup,"child::");
strcat((char *)lookup,elementName);
result = xmlXPathEvalExpression(lookup,context);
free(lookup);
xmlXPathFreeContext(context);
if(result == NULL){
ERROR("error in xmlXPathEvalExpression\n");
return NULL;
}
if(xmlXPathNodeSetIsEmpty(result->nodesetval)){
xmlXPathFreeObject(result);
ERROR("No Element %s found\n",elementName);
//print_element_names((xmlNodePtr)nodePtr);
return NULL;
}
return result;
}
the returned xmlXPathObjectPtr is used to cycle on the single element and
it's possible that during that, get_xml_elements is called again passing as
nodePtr parameter the node obtained from the previous call to
xml_get_elements.
It happens that on the second call I get a segmentation fault creating the
context:
context = xmlXPathNewContext(nodePtr->doc);
here the stack:
malloc () from /lib/libc.so.6
xmlHashCreate () from /usr/lib/libxml2.so.2
xmlXPathNewContext () from /usr/lib/libxml2.so.2
get_xml_elements (nodePtr=0x8057940, elementName=0x804e51d "field",
context=0x0) at xmlParse.c:169
Can someone tell me if I'm doing a well known error, that is: creating a
context by using an element obtained from a previous created and already
freed context?
I hope the question is clear.
Regards
zad
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