testing strategies: generating a XML file

I'm writing a couple of classes that generate xml file. (Details probably not important at the moment).

I wondering the best testing strategy is.

• I don't want to re-write the xml generation code just to compare the output, when I could write the file to disk and compare it at certain milestones (the xml spec won't change often, like once or twice every couple of years)
• I'm more interested in testing the behaviour of the architecture instead of the getters & setters

Options that come to mind:

• rebuilding the xml file in the testing environment and comparing the string representations
• manually checking the result (writing to file, etc)
• rebuilding the xml file in memory in the testing environment and comparing the in-memory elements.

Virtual Bonus if you know any libraries for C++ and/or Google Test.

Ideas?

Have you considered using XSD's and validating your XML to the XSD? You didn't mention if it was content or structure you were testing for (probably both).
If it validates, it will test the structure of the XML will conform to the required structure.