[xml] lot of disk access using libxml2

[flo <flo mataf net>]

Hello,

I use the libxml2 lib to parse and write xml file data.

For this I use the code below:

  /* parse the file */
  doc = xmlParseFile(xmlFile);
  if(doc == NULL) {
    fprintf(stderr, "error: could not parse the file %s\n",xmlFile);
    return 1;
  }

  /* get the root element node */
  cur = xmlDocGetRootElement(doc);
  if(cur == NULL) {
    fprintf(stderr, "empty doc %s\n", xmlFile);
    xmlFreeDoc(doc);
    return 1;
  }

/* code path then the xml data in advancing the pointer "cur" * /
/ * Data is stored in a linked list for processing * /

  /* free the document */
  xmlFreeDoc(doc);

  /* free the global variables that may have been 
   * allocated by the parser */
  xmlCleanupParser();

Working with the linked list, and then write the XML file with the
reprocessed data by calling the function:


writeXmlData(struct accesLC * liste, char * fileOut) {
  int err = 0;
  xmlTextWriterPtr writer;
  xmlChar *tmp;

  /* Create a new xmlWriter for fileOut */
  writer = xmlNewTextWriterFilename(fileOut, 0);
  if(writer == NULL) {
    fprintf(stderr,"writeXmlData: Error creating the xml writer fileout=
%s\n",fileOut);
    return 1;
  }

  /* Start the document with encoding */
  err = xmlTextWriterStartDocument(writer, NULL, "ISO8859-1", NULL);
  if(err < 0) {
    fprintf(stderr,"writeXmlData: Error at xmlTextWriterStartDocument
\n");
    xmlFreeTextWriter(writer);
    return 1;
  }

  /* First element is datafeed */
  err = xmlTextWriterStartElement(writer, BAD_CAST "datafeed");
  if(err < 0) {
    fprintf(stderr,"writeXmlData: Error at xmlTextWriterStartElement for
datafeed\n");
    xmlTextWriterEndDocument(writer);
    xmlFreeTextWriter(writer);
    return 1;
  }
  /* Retour à la ligne */
  err = xmlTextWriterWriteRaw(writer, "\n");
  if(err < 0) {
    fprintf(stderr,"writeXmlData: Error at xmlTextWriterWriteComment
writing date\n");
    xmlTextWriterEndDocument(writer);
    xmlFreeTextWriter(writer);
    return 1;
  }
  
  while(liste->last != NULL) {

    /* Secund element is point, as child of datafeed */
    err = xmlTextWriterStartElement(writer, BAD_CAST "point");
    if(err < 0) {
      fprintf(stderr,"writeXmlData: Error at xmlTextWriterStartElement
for point\n");
      xmlTextWriterEndDocument(writer);
      xmlFreeTextWriter(writer);
      return 1;
    }
      
    /* Add the attribute f101 f102 f103 f104 with his value */
    err = xmlTextWriterWriteFormatAttribute(writer, BAD_CAST "f101", "%
f", 
                                            liste->last->data->f101);
    if(err < 0) {
      fprintf(stderr,"writeXmlData: Error at xmlTextWriterWriteAttribute
for correl\n");
      xmlTextWriterEndDocument(writer);
      xmlFreeTextWriter(writer);
      return 1;
    }

    err = xmlTextWriterWriteFormatAttribute(writer, BAD_CAST "f102", "%
f", 
                                            liste->last->data->f102);
    if(err < 0) {
      fprintf(stderr,"writeXmlData: Error at xmlTextWriterWriteAttribute
for correl\n");
      xmlTextWriterEndDocument(writer);
      xmlFreeTextWriter(writer);
      return 1;
    }

    err = xmlTextWriterWriteFormatAttribute(writer, BAD_CAST "f103", "%
f", 
                                            liste->last->data->f103);
    if(err < 0) {
      fprintf(stderr,"writeXmlData: Error at xmlTextWriterWriteAttribute
for correl\n");
      xmlTextWriterEndDocument(writer);
      xmlFreeTextWriter(writer);
      return 1;
    }

    err = xmlTextWriterWriteFormatAttribute(writer, BAD_CAST "f104", "%
f", 
                                            liste->last->data->f104);
    if(err < 0) {
      fprintf(stderr,"writeXmlData: Error at xmlTextWriterWriteAttribute
for correl\n");
      xmlTextWriterEndDocument(writer);
      xmlFreeTextWriter(writer);
      return 1;
    }

    /* Write the date as child of point */
    err = xmlTextWriterWriteFormatRaw(writer, "%s",
liste->last->data->date);
    if(err < 0) {
      fprintf(stderr,"writeXmlData: Error at xmlTextWriterWriteComment
writing date\n");
      xmlTextWriterEndDocument(writer);
      xmlFreeTextWriter(writer);
      return 1;
    }

    /* Close the element named point */
    err = xmlTextWriterEndElement(writer);
    if(err < 0) {
      fprintf(stderr,"writeXmlData: Error at xmlTextWriterEndElement for
point err=%d\n", err);
      xmlTextWriterEndDocument(writer);
      xmlFreeTextWriter(writer);
      return 1;
    }

    /* Retour à la ligne */
    err = xmlTextWriterWriteRaw(writer, "\n");
    if(err < 0) {
      fprintf(stderr,"writeXmlData: Error at xmlTextWriterWriteComment
writing date\n");
      xmlTextWriterEndDocument(writer);
      xmlFreeTextWriter(writer);
      return 1;
    }

    liste->last = liste->last->prev;
  } 

  /*fin du document */
  /* Here we could close the elements datafeed using the
   * function xmlTextWriterEndElement, but since we do not want to
   * write any other elements, we simply call xmlTextWriterEndDocument,
   * which will do all the work. */
  err = xmlTextWriterEndDocument(writer);
  if (err < 0) {
    fprintf(stderr,"writeXmlData : Error at xmlTextWriterEndDocument
\n");
    xmlFreeTextWriter(writer);
    return 1;
  }
  
  xmlFreeTextWriter(writer);

  return 0;
}

My problem: This code generates a lot of disk access. I wanted to know
if I use the correct lib libxml2 to write my file?

I understand the appeal: writer = xmlNewTextWriterFilename (fileout, 0);
allows me to work with a memory pointer and that the call to:
xmlTextWriterEndDocument (), which is writing to disk.

Am I wrong??

thank you for your responses.

Flo