Re: MemBufFormatTarget possible bug

[Alberto Massari]

[EMAIL PROTECTED] wrote:
hi Alberto
indeed, now it is ok. thank you, i have not much experience with Janitor.

I have another question about Janitor or AutoDelete Template Classes, because i 
saw them in many examples. What are the big difference between them and when 
should i use these classes.

  

A Janitor or a AutoDelete object is used as a stack variable when you 
want to delete an object allocated in the heap as soon as it goes out of 
scope (because of normal execution flow, or because of an exception).
That is,

 try
 {
   Janitor<Type> j(new Type(...));
   ...
 }
 catch(....) {}

is the same of

 Type* p=new Type(..);
 try
 {
   ...
 }
 catch(...) {}
 delete p;

Alberto


greetings
   Affe


-------- Original-Nachricht --------
  
Datum: Fri, 11 Apr 2008 10:13:58 +0200
Von: Alberto Massari <[EMAIL PROTECTED]>
An: c-users@xerces.apache.org
Betreff: Re: MemBufFormatTarget possible bug
    

  
Affe,
the memory becomes corrupted because you create the MemBufFormatTarget 
using the memory manager belonging to the DynamicContext stored in the 
dynamic_context Janitor variable; but once that you exit from the 
try/catch block, the context is deleted, the memory it allocated is 
deleted, and the storage used by the MemBufFormatTarget is gone (it can 
still contain the original data, or just pieces of it, but it could also 
trigger access violations).
You should move the code that copies the result of the query into the 
std::string inside the try/catch block, or move the dynamic_context out 
of it.

Alberto

[EMAIL PROTECTED] wrote:
    
hi Alberto

can you please try my example again, now i have a complete copy&paste
      
programm, maybe i do some wrong initializing. thanks
    
my output is always (the first character should be '<b b':

length :70
1n="b1">      some b1 text</b>
<b b2n="b2">      some b2 text</b>




#include <iostream>
#include <vector>
#include <map>

#include <xercesc/framework/StdOutFormatTarget.hpp>
#include <xercesc/framework/LocalFileFormatTarget.hpp>
#include <xercesc/util/XMLUri.hpp>
#include <xercesc/parsers/XercesDOMParser.hpp>
#include <xercesc/framework/MemBufInputSource.hpp>
#include <xercesc/util/OutOfMemoryException.hpp>
#include <xercesc/framework/MemBufFormatTarget.hpp>

//XQilla includes
#include <xqilla/xqilla-simple.hpp>
#include <xqilla/ast/LocationInfo.hpp>
#include <xqilla/context/MessageListener.hpp>
#include <xqilla/utils/PrintAST.hpp>
#include <xqilla/events/EventSerializer.hpp>
#include <xqilla/events/NSFixupFilter.hpp>
#include <xqilla/xerces/XercesConfiguration.hpp>
#include <xqilla/fastxdm/FastXDMConfiguration.hpp>
#include <xqilla/utils/XQillaPlatformUtils.hpp>

#if defined(XERCES_HAS_CPP_NAMESPACE)
XERCES_CPP_NAMESPACE_USE
#endif

using namespace std;

#define QUERY_BUFFER_SIZE 32 * 1024
#define BASEURI_BUFFER_SIZE 2 * 1024


int main(int argc, char *argv[])
{
  
	XMLPlatformUtils::Initialize();
        XQillaPlatformUtils::initialize();


        XercesDOMParser *parser = new XercesDOMParser();
    parser->setValidationScheme(XercesDOMParser::Val_Auto);
    parser->setDoNamespaces(true);
    parser->setDoSchema(false);
    parser->setValidationSchemaFullChecking(false);
    parser->setCreateEntityReferenceNodes(false);


        std::string xml("\
<test>\
      <b b1n='b1'> some b1 text\
    </b>\
    <b b2n='b2'>some b2 text\
    </b>\
    <a url='test.xml' name='aaaa'/>\
</test>\
");

 MemBufInputSource*memBufIS = new MemBufInputSource
 (
        (const XMLByte*)xml.c_str()
        , xml.length()
        , "somedoc"
        , false
 );


 try
    {
        parser->parse(*memBufIS);
    }
    catch (const OutOfMemoryException&)
    {
        cout<<"OutOfMemoryException"<<endl;
    }
    catch (const XMLException& e)
    {
        cout << "XMLException" << endl;
    }
    
    catch (...)
    {
        cout << "some unnown exception" << endl;
    }
    DOMNode*root = parser->getDocument()->getFirstChild();
    ((DOMDocument*)parser->getDocument())->setDocumentURI(0);


    XercesConfiguration xercesConf;
    XQillaConfiguration *conf = &xercesConf;
    XQilla xqilla;
    int language = XQilla::XQUERY;
    language |= XQilla::UPDATE;
     Janitor<DynamicContext> contextGuard
        (xqilla.createContext((XQilla::Language)language, conf));
    DynamicContext *context = contextGuard.get();

    context->setXPath1CompatibilityMode(false);  
    MemBufFormatTarget*memtarget=0;


try{
    XQQuery *query = xqilla.parse(

        //query 1  (only corrupt when mem=1024)
        //X("declare revalidation skip;/test/b")

                //query 2 (always corrupt)
                X("for $i in (1 to 2)\
return\
<b>\
{attribute {concat('b', $i, 'n')} {concat('b',$i)}}\
      some b{$i} text\
</b>")

        ,contextGuard.release()
            );
    Janitor<DynamicContext>
      
dynamic_context(query->createDynamicContext());
    
    Node::Ptr node = xercesConf.createNode(root,dynamic_context.get());
    dynamic_context->setContextItem(node.get());
    dynamic_context->setContextPosition(1);
    dynamic_context->setContextSize(1);


    int mem=0;
        //int mem=1024;
   memtarget = new MemBufFormatTarget(mem,
                      dynamic_context->getMemoryManager());
   EventSerializer writer("UTF-8", "1.1", memtarget,  
            dynamic_context->getMemoryManager());
   writer.addNewlines(true);
   NSFixupFilter nsfilter(&writer, dynamic_context->getMemoryManager());
   query->execute(&nsfilter, dynamic_context.get());
   }
  catch(XQException &e) {}

    int count = memtarget->getLen()*sizeof(XMLByte);
    string result((char*)memtarget->getRawBuffer(),
                    count);
    cout << "length :" << count << endl;
        cout <<  result << endl;

        XMLPlatformUtils::Terminate();
    XQillaPlatformUtils::terminate();
return 0;
}


greetings
   Affe