无法使用libxml2处理xpath查询

Question

I have below mentioned xml path query

//Namespace char* pszNs_Soap_prefix = "s"; char* pszNs_Soap_URL = " http://schemas.xmlsoap.org/soap/envelope/ ";

char* pszNs_SamlP_Prefix = "sp"; char* pszNS_SamlP_URL = "urn:oasis:names:tc:SAML:1.0:protocol";

char* pszNS_Saml_Prefix = "sl"; char* pszNS_Saml_URL = "urn:oasis:names:tc:SAML:1.0:assertion";

char* pszXPathQuery3 = "/s:Envelope/s:Body/sp:Response/sl:Assertion/sl:AttributeStatement/s1:Attribute[@AttributeName='role']/sl:AttributeValue";

but getting NULL from xmlXPathEvalExpression library function,above is my xpath query, don't know where i am going wrong.

m_pXmlXPathObject=xmlXPathEvalExpression((xmlChar*)pszXPathQuery,m_pXmlXPathContext);

XML string

                                <saml:Assertion MajorVersion="1"
                                                        MinorVersion="1"
                                                        AssertionID="_a75adf55-01d7-40cc-929f-dbd8372ebdfc"
                                                        Issuer="SAML_AUTH_URI"
                                                        IssueInstant="2005-06-08T12:00:01.100Z">
                                        <saml:AuthenticationStatement
                                                        AuthenticationMethod="urn:oasis:names:tc:SAML:1.0:am:password"
                                                        AuthenticationInstant="2005-06-08T11:59:59.000Z">
                                                <saml:Subject>
                                                        <saml:NameIdentifier>jre</saml:NameIdentifier>
                                                </saml:Subject>
                                        </saml:AuthenticationStatement>
                                        <saml:AttributeStatement>
                                                <saml:Attribute
                                                                AttributeName="role"
                                                                AttributeNamespace="oasis:names:tc:xacml:2.0:subject">
                                                        <saml:AttributeValue>weboamadmin</saml:AttributeValue>
                                                </saml:Attribute>
                                        </saml:AttributeStatement>
                                </saml:Assertion>

                        </samlp:Response>
                </SOAP-ENV:Body>

        </SOAP-ENV:Envelope>

Answer 1

The problem is that you need to register your name spaces BEFORE you execute your xpath query. The xmlsoft.org website gives a good example on how to perform this!

http://xmlsoft.org/examples/xpath1.c