Although I have contributed to a few (free) scientific applications (in C and
F77) for quite some time, I'm new to xml and libxml2 (this may explain the
naiveté of my question): I'm writing a C parser for an XML input (input only,
no file editing or writing out) - so the xmlTextReader API
(http://xmlsoft.org/xmlreader.html#L1142) seems very appropriate. I have gone
through the tutorial and am now in the process of integrating DTD validation.
The DTD validation correctly flags errors, but I can't seem to add appropriate
code to halt the scanning process once a first parsing error occurs (the code
below - lightly adapted from the tutorial - simply goes on and on, parsing the
entire file despite the initial DTD parsing errors): --- C code ---
1. #include <stdlib.h>
2. #include <stdio.h>
3. #include <libxml/xmlreader.h>
4.
5. static void processNode( xmlTextReaderPtr reader )
6. {
7. xmlChar *name, *value;8. name = xmlTextReaderName( reader );
9. if( name != NULL ) printf( "element '%s'\n", name );
10. xmlFree( name );
11. }
12.
13. void streamXMLFile(char *filename)
14. {
15. xmlTextReaderPtr reader;
16. int ret = 0;
17.
18. reader = xmlNewTextReaderFilename( filename );
19.
20. if( reader != NULL )
21. {
22. ret = xmlTextReaderSetParserProp( reader, XML_PARSER_VALIDATE, 1 );
23. printf( "ret = %d\n", ret );
24. ret = xmlTextReaderRead( reader );
25. printf( "ret = %d\n", ret );
26. while( ret == 1 )
27. {
28. processNode( reader );
29. ret = xmlTextReaderRead( reader );
30. printf( "ret = %d\n", ret );
31. }
32. xmlFreeTextReader(reader);
33. }
34. else printf("Unable to open %s\n", filename);35. }--- end of C code ---
--- example XML file (with DTD error: lines 7. versus 12.) ---1. <?xml
version="1.0"?>2. <!DOCTYPE a [3. <!ELEMENT a (b*)>4. <!ELEMENT b
(c,d)>5. <!ATTLIST b r ID #REQUIRED>6. <!ELEMENT c (#PCDATA)>7.
<!ELEMENT d (#PCDATA)>8. ]>9. <a>10. <b r="one">11. <c>un</c>12.
<duh>0.10</duh>13. </b>14. <b r="two">15. <c>deux</c>16. <d>0.20</d>17. </b>18.
</a>--- end of example XML file --- --- screen output (using the DTD incorrect
XML file above) ---ret = 0test.xml:15: element duh: validity error : No
declaration for element duh<duh>0.10</duh> ^test.xml:16: element
b: validity error : Element b content does not follow the DTD, expecting (c ,
d), got (c duh )</b> ^ret = 1element 'a'element 'a'element '#text'element
'b'element '#text'element 'c'element '#text'element 'c'element
'#text'test.xml:24: element b: validity error : Element b content does not
follow the DTD, Misplaced duh^test.xml:24: element duh: validity error : No
declaration for element duh^element 'duh'element '#text'element 'duh'element
'#text'element 'b'element '#text'element 'b'element '#text'element 'c'element
'#text'element 'c'element '#text'element 'd'element '#text'element 'd'element
'#text'element 'b'element '#text'element 'a'--- end of screen output
---Question 1: How does one halt the entire process and alert the user (e.g.
using the variable ret, maybe streaming the XML screen output to a string
buffer) once a first parsing error occurs? Question 2: The screen output
indicates that the DTD error (lines 7. versus 12.) is immediately flagged after
the first xmlTextReaderRead call (line 24.); if the xmlTextReader only scans
one element node at a time, how can it initially flag this error (which only
occurs later)? Is it building an entire DOM tree to do this? Thank you in
advance for your help!
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