How to get attributes from a node in libxml2

Question

I am working on a parser to get data from an XML file. I am using libxml2 to extract data. I am a not able to get the attributes from nodes. I only found nb_attributes to get the count of the attributes.

Answer 1

I think joostk meant attribute->children, giving something like this:

xmlAttr* attribute = node->properties;
while(attribute)
{
  xmlChar* value = xmlNodeListGetString(node->doc, attribute->children, 1);
  //do something with value
  xmlFree(value); 
  attribute = attribute->next;
}

See if that works for you.

Answer 2

Try something like:

xmlNodePtr node; // Some node
NSMutableArray *attributes = [NSMutableArray array];

for(xmlAttrPtr attribute = node->properties; attribute != NULL; attribute = attribute->next){
    xmlChar *content = xmlNodeListGetString(node->doc, attribute->children, YES);
    [attributes addObject:[NSString stringWithUTF8String:content]];
    xmlFree(content);
}

Answer 3

I think I found why you only got 1 attribute (at least it happened to me).

The problem was that I read attributes for first node but next is a text node. Don't know why, but node->properties gives me a reference to a non-readable part of memory, so it crashed.

My solution was to check node type (element is 1)

I'm using a reader, so:

xmlTextReaderNodeType(reader)==1

The entire code you can get it from http://www.xmlsoft.org/examples/reader1.c and add this

xmlNodePtr node= xmlTextReaderCurrentNode(reader);
if (xmlTextReaderNodeType(reader)==1 && node && node->properties) {
    xmlAttr* attribute = node->properties;
    while(attribute && attribute->name && attribute->children)
    {
      xmlChar* value = xmlNodeListGetString(node->doc, attribute->children, 1);
      printf ("Atributo %s: %s\n",attribute->name, value);
      xmlFree(value);
      attribute = attribute->next;
    }
}

to line 50.

Answer 4

The easiest way I found using libxml2 (through libxml++ in C++) was to use the eval_to_XXX methods. They evaluate an XPath expression, so you need to use the @property syntax.

For example:

std::string get_property(xmlpp::Node *const &node) {
    return node->eval_to_string("@property")
}

Answer 5

if you just want a single attribute, use xmlGetProp or xmlGetNsProp

Answer 6

If you use SAX method startElementNs(...), this function is what you are looking for:

xmlChar *getAttributeValue(char *name, const xmlChar ** attributes,
           int nb_attributes)
{
int i;
const int fields = 5;    /* (localname/prefix/URI/value/end) */
xmlChar *value;
size_t size;
for (i = 0; i < nb_attributes; i++) {
    const xmlChar *localname = attributes[i * fields + 0];
    const xmlChar *prefix = attributes[i * fields + 1];
    const xmlChar *URI = attributes[i * fields + 2];
    const xmlChar *value_start = attributes[i * fields + 3];
    const xmlChar *value_end = attributes[i * fields + 4];
    if (strcmp((char *)localname, name))
        continue;
    size = value_end - value_start;
    value = (xmlChar *) malloc(sizeof(xmlChar) * size + 1);
    memcpy(value, value_start, size);
    value[size] = '\0';
    return value;
}
return NULL;
}

Usage:

char * value = getAttributeValue("atrName", attributes, nb_attributes);
// do your magic
free(value);