CODEWITHSUNDEEP
cmemory-leakssegmentation-faultlibxml2
Salahuddin
Salahuddin

Reputation: 1719

libxml2 - Why does xmlFreeNode() causes a segmentation fault?

I'm trying to minimize memory leaks caused by libxml2.

I free the xmlDoc without problem. But when I try to free xmlNode it causes segmentation fault. In this case, it -somehow- prevents the program from finding the file, then xmlReadFile returns a NULL pointer and consequently xmlDocGetRootElement also returns a NULL pointer and trying to accessing root_element causes a segmentation fault.

If I just commented out the lines with xmlFreeNode(), everything works fine.

Just to double check, I tried to check if the node pointers are not NULL before trying to freeing the nodes, but this doesn't help.

Why can't I free the nodes without problems?

int setKey(uint8 newState)
{
    xmlDocPtr doc = NULL;
    xmlNodePtr root_element = NULL;
    xmlNodePtr cur_node = NULL;

    char newChar[3];

    const char *file = "file.xml";

    doc = xmlReadFile(file, NULL, 0);

    sprintf(newChar, "%d", newState);

    root_element = xmlDocGetRootElement(doc);

    cur_node = root_element->children; // segmentation fault

    xmlNodeSetContent(cur_node, (const xmlChar *)newChar);

    xmlSaveFile(file, doc);

    xmlFreeDoc(doc);
    if(cur_node != NULL && root_element != NULL)
    {
        xmlFreeNode(cur_node);
        xmlFreeNode(root_element);
    }

    return 1;
}

Upvotes: 1

Views: 1117

Answers (1)

nwellnhof
nwellnhof

Reputation: 33618

xmlFreeDoc frees a document and all descendant nodes recursively. So freeing individual nodes again causes a double-free which typically results in a segfault. If you want to keep some of the nodes after freeing the document, you have to unlink them with xmlUnlinkNode first.

Upvotes: 2

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