Xerces C++ schema parsing

I am parsing a complex schema using Xerces C++. I need to read the "fixed" values of attribute declarations within element declarations.

For example:

<xsd:element name="SampleElement">
<xsd:complexType>
<xsd:complexContent>
<xsd:extension base="SampleElementType">
<xsd:attribute name="sampleName" type="xsd:string" fixed="XXXXXXXXXX">
</xsd:attribute>
</xsd:extension>
</xsd:complexContent>
</xsd:complexType>
</xsd:element>

In this schema exerpt, I would need to read the value "XXXXXXXXXX" from the attribute declaration "sampleName". I have been able to get as far as reading the element declaration into an object of type XSElementDeclaration, and from there I am able to read the attribute declaration into an object of type XSAttributeDeclaration. However, I have not been able to find a method to return the value of the fixed content of the attribute declaration.

A small snipet of my code:

XSAttributeDeclaration *xsAttributeDeclaration;

.
.
.

//After reading the attribute declaration into the xsAttributeDeclaration variable
CString csFixedValue = xsAttributeDeclaration->getConstraintValue();

The "getConstraintValue()" method is returning an empty string when I thought it should be returning the value of the fixed constraint.

The question:

Am I using the "getConstraintValue()" method improperly, or is it the wrong method to be using altogether? If it is the wrong method, how can I get the "fixed" value from the attribute declaration using an object of type XSAttributeDeclaration? I have tried to be as specific as necessary, but I am happy to give out more information should it be needed. Any and all help is appreciated greatly!