没有此类属性时 DOMElement::getAttribute() 返回空字符串的原因

Question

In the php docs it says:

Return Values

The value of the attribute, or an empty string if no attribute with the given name is found.

Does anybody know the reason for returning an empty string instead of just NULL ?

Answer 1

The point is that the DOM specification is not platform-specific. It was written to be implemented in a wide variety of programming languages, so it tends not to assume the existence of types such as null . The W3C can assume the existence of a string type, so it's safe to use an empty string.

So the specification reads as this:

DOMString                 getAttribute(in DOMString name);

So a string is the expected type on a cross-platform basis. PHP's DOMDocument conforms to this.

Answer 2

I don't think it really matters what it returns. To check the validity of the result you need to call DOMElement::hasAttribute() anyway.

It could be just because they want to keep it simple and have everything return strings instead of a magic value of a different type (like null ).