Working with attributes: xml_set and xml_attrval

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Setting an attribute is a little complicated. If the attribute is already represented in the element's attribute list, then we free the old value, allocate space for a copy of the new value, and copy it. Otherwise we allocate a new attribute holder and copy both name and value into it.
  
void xml_set (XML * xml, const char * name, const char * value)
{
   ATTR * attr;

   attr = xml->attrs;
   while (attr) {
      if (!strcmp (attr->name, name)) break;
      attr = attr->next;
   }

   if (attr) {
      free ((void *) (attr->value));
      attr->value = (char *) malloc (strlen (value) + 1);
      strcpy (attr->value, value);
      return;
   }

   if (xml->attrs == NULL) {
      attr = (ATTR *) malloc (sizeof (struct _attr));
      xml->attrs = attr;
   } else {
      attr = xml->attrs;
      while (attr->next) attr = attr->next;
      attr->next = (ATTR *) malloc (sizeof (struct _attr));
      attr = attr->next;
   }

   attr->next = NULL;
   attr->name = (char *) malloc (strlen (name) + 1);
   strcpy (attr->name, name);
   attr->value = (char *) malloc (strlen (value) + 1);
   strcpy (attr->value, value);
}
void xml_setnum (XML * xml, const char *attr, int number)
{
   char buf[sizeof(number) * 3 + 1];
   sprintf (buf, "%d", number);
   xml_set (xml, attr, buf);
}
Retriving a value, on the other hand, is rather simple.
  
const char * xml_attrval (XML * element,const char * name)
{
   ATTR * attr;

   attr = element->attrs;
   while (attr) {
      if (!strcmp (attr->name, name)) return (attr->value);
      attr = attr->next;
   }
   return ("");
}
int xml_attrvalnum (XML * element, const char * name)
{
   return (atoi (xml_attrval (element, name)));
}
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