IPhone SDK extract PDF text

Question

I used some 2D Quartz examples to extract text from a PDF using callbacks.

CGPDFOperatorTableSetCallback(table, "TJ", arrayCallback);
CGPDFOperatorTableSetCallback(table, "Tj", stringCallback);

Link to the code from here: Reading PDF files as a string through the iPhone app

But in some PDFs, I can’t get the entire contents of the string (and yes, this is the string). How can I parse the BT (beginning of text) and ET (final text) statements using the C function?

Thank.