fop without temporary file

first of all, sorry for my english.
how can i use fop to generate pdf, without creating a temporary XML file.

now I have a xsl file, and then create a temporary xml file,  and  execute
"fop -xsl file.xsl -xml file.xml  -pdf file.pdf". but i must to  delete
file.xml leter.

how can I  generate pdf without creating temporary xml file?  how to explain
to FOP get xml data from string?
p.s.   i am using C++.  exec FOP  from execv();