XPathExpression::Compile Method (String^)
Compiles the XPath expression specified and returns an XPathExpression object representing the XPath expression.
Assembly: System.Xml (in System.Xml.dll)
Parameters
- xpath
-
Type:
System::String^
An XPath expression.
| Exception | Condition |
|---|---|
| ArgumentException | The XPath expression parameter is not a valid XPath expression. |
| XPathException | The XPath expression is not valid. |
An XPath expression is evaluated to yield one of the following result types.
Note |
|---|
If a user-defined function with an invalid number of arguments (or an unimplemented user-defined function) is specified in the XPath expression, an exception occurs only at run time. User-defined functions are not checked at compile time and exceptions that result from user-defined functions occur only if execution evaluates the expression. |
The following example shows how to use the XPath return type to determine how to process the XPath expression. The example uses the Compile method to return the new XPathExpression objects.
public ref class Sample { public: static void Evaluate( XPathExpression^ expr, XPathNavigator^ nav ) { XPathNodeIterator^ i = nav->Select(expr); switch ( expr->ReturnType ) { case XPathResultType::Number: Console::WriteLine( nav->Evaluate( expr ) ); break; case XPathResultType::NodeSet: while ( i->MoveNext() ) Console::WriteLine( i->Current ); break; case XPathResultType::Boolean: if ( *safe_cast<bool^>(nav->Evaluate( expr )) ) Console::WriteLine( "True!" ); break; case XPathResultType::String: Console::WriteLine( nav->Evaluate( expr ) ); break; } } }; int main() { XPathDocument^ doc = gcnew XPathDocument( "contosoBooks.xml" ); XPathNavigator^ nav = doc->CreateNavigator(); XPathExpression^ expr1 = nav->Compile( ".//price/text()*10" ); // Returns a number. XPathExpression^ expr2 = nav->Compile( "bookstore/book/price" ); // Returns a nodeset. Sample^ MySample = gcnew Sample; MySample->Evaluate( expr1, nav ); MySample->Evaluate( expr2, nav ); }
The example takes the contosoBooks.xml file as input.
<?xml version="1.0" encoding="utf-8" ?> <bookstore xmlns="http://www.contoso.com/books"> <book genre="autobiography" publicationdate="1981-03-22" ISBN="1-861003-11-0"> <title>The Autobiography of Benjamin Franklin</title> <author> <first-name>Benjamin</first-name> <last-name>Franklin</last-name> </author> <price>8.99</price> </book> <book genre="novel" publicationdate="1967-11-17" ISBN="0-201-63361-2"> <title>The Confidence Man</title> <author> <first-name>Herman</first-name> <last-name>Melville</last-name> </author> <price>11.99</price> </book> <book genre="philosophy" publicationdate="1991-02-15" ISBN="1-861001-57-6"> <title>The Gorgias</title> <author> <name>Plato</name> </author> <price>9.99</price> </book> </bookstore>
Available since 2.0
Silverlight
Available since 4.0
