http://www.pmsf.de/resources/lisp/expat.html

I have written a basic C wrapper for libmxl2, which parses an XML
document, and prints a list containing the parsed data.  At the moment,
I save the printed sexp to a file, and READ it from Lisp.  I am thinking
it may be better to avoid the intermediate printing and READing, and
instead save the parsed data to a C struct; I can then try to use Lisp
to get the sexp from the C struct, using an FFI.  What is a good way to
store a sexp in C?  Is it common practice to pass through an
intermediate file like I am doing now?

TIA,
Raghavendra.

PS: In case it's relevant, the C wrapper takes an XML document like this

--8<---------------cut here---------------start------------->8---
<?xml version="1.0" encoding="utf-8"?>
<?draft omit="author"?>
<doc xmlns="urn:example:ns:doc"
     xmlns:kw="urn:example:ns:keyword"
     xmlns:xi="http://www.w3.org/2001/XInclude"
     id="sexp" lang="en-GB">
  <?latex class="article" fontsize="12pt"?>
  <docinfo>
    <author>
      <firstname>Schöne</firstname>
      <surname>Grüße</surname>
    </author>
    <title>An Example Article</title>
    <titleabbrev role="running-title">Example art</titleabbrev>
    <keywordset>
      <keyword kw:type="ai">an articleinfo keyword</keyword>
      <keyword kw:type="ai">another articleinfo keyword</keyword>
    </keywordset>
  </docinfo>
  <xi:include href="urn:publicid:-:EXAMPLE:DOCUMENT+Section:EN"/>
</doc>
--8<---------------cut here---------------end--------------->8---

and prints a sexp, which when READ by CLISP looks like this

--8<---------------cut here---------------start------------->8---
((DRAFT (PROCESSING-INSTRUCTION "omit=\"author\""))
 (DOC (XML-NAMESPACE "urn:example:ns:doc") (ID "sexp") (LANG "en-GB")
  (LATEX (PROCESSING-INSTRUCTION "class=\"article\" fontsize=\"12pt\""))
  (DOCINFO (XML-NAMESPACE "urn:example:ns:doc")
   (AUTHOR (XML-NAMESPACE "urn:example:ns:doc")
    (FIRSTNAME (XML-NAMESPACE "urn:example:ns:doc") "Schöne")
    (SURNAME (XML-NAMESPACE "urn:example:ns:doc") "Grüße"))
   (TITLE (XML-NAMESPACE "urn:example:ns:doc") "An Example Article")
   (TITLEABBREV (XML-NAMESPACE "urn:example:ns:doc") (ROLE "running-title")
    "Example art")
   (KEYWORDSET (XML-NAMESPACE "urn:example:ns:doc")
    (KEYWORD (XML-NAMESPACE "urn:example:ns:doc")
     (TYPE (XML-NAMESPACE "urn:example:ns:keyword") "ai")
     "an articleinfo keyword")
    (KEYWORD (XML-NAMESPACE "urn:example:ns:doc")
     (TYPE (XML-NAMESPACE "urn:example:ns:keyword") "ai")
     "another articleinfo keyword")))
  (SECTION
   (SECTIONINFO
    (KEYWORDSET
     (KEYWORD (TYPE (XML-NAMESPACE "urn:example:ns:keyword") "si")
      "a sectioninfo keyword")))
   (TITLE "A Section")
   (PARA
    "This is a paragraph in a section.  It does not quote any one,
  so we don't need any `\"' characters.")
   (PARA "The canonical URI for this document is "
    (ULINK (URL "http://www.example.org/sexp"))
    ".  Please check there for the
  latest updates.  Meanwhile, here is Äñ example of
  character entity references."))))
--8<---------------cut here---------------end--------------->8---