Finding a node in xml file with libxml2 - c

Question

I am trying to write a function that will find a node with a specified name in a xml file.
The problem is that the function never finds the specified node.
xmlNodePtr findNodeByName(xmlNodePtr rootnode, const xmlChar * nodename)
{
xmlNodePtr node = rootnode;
if(node == NULL){
log_err("Document is empty!");
return NULL;
}
while(node != NULL){
if(!xmlStrcmp(node->name, nodename)){
return node;
}
else if(node->children != NULL){
node = node->children;
xmlNodePtr intNode = findNodeByName(node, nodename);
if(intNode != NULL){
return intNode;
}
}
node = node->next;
}
return NULL;
}
I can see in the debugger that function does go deep into the sub nodes but still returns NULL.
Thanks in advance.

Answer 1

else if(node->children != NULL) {
node = node->children;
xmlNodePtr intNode = findNodeByName(node, nodename);
if (intNode != NULL) {
return intNode;
}
}
This should be:
else if (node->children != NULL) {
xmlNodePtr intNode = findNodeByName(node->children, nodename);
if(intNode != NULL) {
return intNode;
}
}
and it works fine

Answer 2

Your function is correct. Add a debugging line to see why it doesn't work in your case. For example:
printf("xmlStrcmp(%s, %s)==%d\n", node->name, nodename,
xmlStrcmp(node->name, nodename));
But you don't really need that function. You may use xmlXPathEval.

Answer 3

When #jarekczek mentionned XPath, he means to use XPath instead of your function.
With XPath, your function will become:
xmlNodeSetPtr findNodesByName(xmlDocPtr doc, xmlNodePtr rootnode, const xmlChar* nodename) {
// Create xpath evaluation context
xmlXPathContextPtr xpathCtx = xmlXPathNewContext(doc);
if(xpathCtx == NULL) {
fprintf(stderr,"Error: unable to create new XPath context\n");
return NULL;
}
// The prefix './/' means the nodes will be selected from the current node
const xmlChar* xpathExpr = xmlStrncatNew(".//", nodename, -1);
xmlXPathObjectPtr xpathObj = xmlXPathNodeEval(rootnode, xpathExpr, xpathCtx);
if(xpathObj == NULL) {
fprintf(stderr,"Error: unable to evaluate xpath expression \"%s\"\n", xpathExpr);
xmlXPathFreeContext(xpathCtx);
return NULL;
}
xmlXPathFreeContext(xpathCtx);
return xpathObj->nodesetval;
}
Note: This function returns all the nodes matching 'nodename'. If you only want the first node, you could replace return xpathObj->nodesetval; by:
if (xpathObj->nodesetval->nodeNr > 0) {
return xpathObj->nodesetval->nodeTab[0];
} else {
return NULL;
}
You could also append [1] to the XPath query to optimize your query.