Is anyone aware of an (open source) XSLT engine, implemented in C++, that would enable the programmer to register a callback for the evaluation of XPath expressions, rather than the processor internally evaluating the expressions from a predetermined input file?

The reason for wanting this behavior is that I wish to perform an XSLT operation using for input a document in an XML database. The database supports XPath but not XSLT. Further, the document in the database is too large to load into memory, and evaluating XPath expressions from a DOM representation would be too slow anyway because it lacks the indices maintained by the database. Thus, the idea here is that whenever the engine needs to evaluate an Xpath expression on the input, the expression is passed to the application through a callback, and the application then submits the expression to the database for evaluation. The database then returns a result node that in turn is returned to the engine. In this way, small result sets are extracted from the XML database into memory, but the entire database document is not, and the XSLT engine is able to process the template not knowing the difference.

Alternatively, if anyone sees another solution to the problem, I would be interested to learn about it.

You can use a C library called libxml2 -> http://www.xmlsoft.org which supports Xpath. I've used it for iOS which allows you to compile C and Objective C. You can Compile C and C++ together, see http://stackoverflow.com/questions/8...x-c-and-c-code

Good Luck

Unfortunately, the discussion of using C and C++ code together does nothing to address the question.

The question asks whether there is an implementation of XSLT with a pluggable XPath evaluator.

libxml does not implement XSLT, so it can't be of value here.

As people have said there is only one C (if that is useful from C++ I don;t know) XSLT processor and that is libxslt: http://xmlsoft.org/XSLT/

I've never heard of any XSLT processor with a plugable Xpath evaluator. There are two ways you could get around this in some XSLT processors, but I don't know if libxslt supports them.

1) Create extension methods which return XML based on whatever code you want.
2) Use the document() function and a custom UrlResolver to return you your database data.

I'm not sure that libxslt support either of these two options though.

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