if (filename != null)
defineDecls = (String) defineDeclarations.get(filename);
defineDecls = prependGlobalDefineDeclarations(defineDecls);
try {
CppFilterReader readIn = new CppFilterReader(in, defineDecls);
Parser p = new Parser(new Lexer(new PushbackReader(readIn, 1024)));
// Parse the file.
Start tree = p.parse();