Node Attributes

It is possible for every element type node in an XML node tree to have attributes.

Attributes are nothing more than a collection of name value pairs. In xmlwrapp, attributes are accessed using the xml::attributes class. This chapter will show you how to work with objects of this class.

Accessing Individual Attributes

The xml::attributes class is a container of node attributes. It would be pretty useless if there was no way to access the individual attributes inside of it. Iterators come to the rescue again. Just like the other xmlwrapp classes, iterators are used to access the attributes stored inside the xml::attributes class.

Attribute Iterators

The xml::attributes::iterator and xml::attributes::const_iterator classes point to a xml::attributes::attr object. This object is what gives you access to the name and value of a given attribute. In future versions of xmlwrapp, you will be able to use this class to access the attribute's namespace.

xml::attributes attrs;

...

xml::attributes::iterator i(attrs.begin());

if (i != attrs.end())
{
  std::cout << " name: " << i->get_name() << "\n";
  std::cout << "value: " << i->get_value() << "\n";
}

Begin and End

If you just wanted to iterate through the attributes, you can use the xml::attributes::begin() and the xml::attributes::end() member functions. They both return either a xml::attributes::iterator or xml::attributes::const_iterator object depending on whether the xml::attributes object is const or not.

Finding Attributes

When you want to locate an attribute with a given name, you can use the xml::attributes::find() member function. It will return an iterator that points to the found attribute or an iterator that is equal to the iterators that the xml::attributes::end() function returns.

There is a small difference between the xml::attributes::find() function and just using the xml::attributes::begin() function to iterate over the attributes. If the attributes belong to a xml::document object that has been validated, the xml::attributes::find() function may return an attribute that was not given in the XML document but contains a default value in the DTD.

If you are asking the xml::attributes::find() function to find an attribute that has a default value, but was present in the XML document, the document version of the attribute is returned.

Adding and Replacing Attributes

Since only one attribute with a given name can exist in a node at any one time, the same function can be used to both add and replace attributes. When attempting to add an attribute who has the same name as another attribute in the container, the old attribute will be removed before the new one is inserted.

To add or replace an attribute, you can use the xml::attributes::insert() member function. It takes the name and value for the attribute to insert.

Removing Attributes

There are two ways to remove an attribute from a xml::attributes object. Both involve a call to the xml::attributes::erase() member function. You can remove an attribute by name, or using an iterator that points to the attribute you wish to remove.