Write transform output to a buffer

[Nithya Nirmal Vijayakumar <nv...@cs.indiana.edu>]

Hi,

I am a new user to Xalan-C++. I want to apply xsl transformation to xml
stored in a buffer and get the output into a buffer.  The
StreamTransform.cpp example reads from a buffer and writes output to a
stream. I want to make this write to a buffer. I saw some discussion about
this in this group and tried following the advice of extending
Callbackhandler. But I am getting many compilation errors. Has anyone
already done this? Could you please post your code? Any help will be
greatly appreciated.

This is what I tried:

//Declaration of wrapper class
XALAN_USING_XALAN(XalanOutputStream)
class xalan_string_stream:public XalanOutputStream{
   private:
          char *output;
          char *buffer;
          unsigned cursor;
   public:
    xalan_string_stream(MemoryManagerType
 XALAN_DEFAULT_CONSTRUCTOR_MEMORY_MGR,
  	size_type theBufferSize = eDefaultBufferSize,
  	size_type theTranscoderBlockSize = eDefaultTranscoderBlockSize,
          bool fThrowTranscodeException = true){
      buffer=new char[1024];
    }

    ~xalan_string_stream(){}

    void writeData (const char *input, size_type length){
      bcopy(input,buffer,length);
    }

    void doFlush (){
    }

    char *get_result(){
      return buffer;
    }
 };

//usage inside main
        istrstream  theXMLStream(theInputDocument,
 strlen(theInputDocument));

        istrstream  theXSLStream(theStyleSheet, strlen(theStyleSheet));

        XALAN_USING_XALAN(XalanDOMString)
        XALAN_USING_XALAN(XalanOutputStreamPrintWriter)
        XALAN_USING_XALAN(XSLTResultTarget)
        XALAN_USING_XALAN(XSLTInputSource)

        XSLTInputSource inputSource(&theXSLStream);

        inputSource.setSystemId(XalanDOMString("foo").c_str());

        const xalan_string_stream *outputStream = new xalan_string_stream();

        XalanOutputStreamPrintWriter *printWriter=new
 XalanOutputStreamPrintWriter((XalanOutputStream &)outputStream, false);

        XSLTResultTarget target(printWriter);

        theResult = theXalanTransformer.transform(&theXMLStream,
 inputSource,target);

//compilation error obtained
 BufferTransform.cpp:40: base `xalanc_1_10::XalanOutputStream' with only
     non-default constructor in class without a constructor
 BufferTransform.cpp:54: ISO C++ forbids defining types within return type
 BufferTransform.cpp:54: destructors must be member functions
 BufferTransform.cpp:54: return type specification for destructor invalid
 BufferTransform.cpp:56: type specifier omitted for parameter `size_type'
 BufferTransform.cpp:56: syntax error before `)' token
 BufferTransform.cpp: In function `void writeData(...)':
 BufferTransform.cpp:57: `input' undeclared (first use this function)
 BufferTransform.cpp:57: (Each undeclared identifier is reported only once
 for each function it appears in.)
 BufferTransform.cpp:57: `buffer' undeclared (first use this function)
 BufferTransform.cpp:57: `length' undeclared (first use this function)
 BufferTransform.cpp: At global scope:
 BufferTransform.cpp:66: syntax error before `}' token
 BufferTransform.cpp: In function `int transform(const char*, char*)':
 BufferTransform.cpp:155: ISO C++ forbids declaration of
 `xalan_string_stream'
     with no type
 BufferTransform.cpp:155: uninitialized const `xalan_string_stream'
 BufferTransform.cpp:155: syntax error before `*' token
 BufferTransform.cpp:157: `outputStream' undeclared (first use this
 function)
 make: *** [all] Error 1


thanks,
Nithya

Re: Write transform output to a buffer

[David Bertoni <db...@apache.org>]

Nithya Nirmal Vijayakumar wrote:
> Hi,
> 
> I am a new user to Xalan-C++. I want to apply xsl transformation to xml
> stored in a buffer and get the output into a buffer.  The
> StreamTransform.cpp example reads from a buffer and writes output to a
> stream. I want to make this write to a buffer. I saw some discussion about
> this in this group and tried following the advice of extending
> Callbackhandler. But I am getting many compilation errors. Has anyone
> already done this? Could you please post your code? Any help will be
> greatly appreciated.

The simplest thing is to use the class ostrstream.  I've attached a diff 
for the StreamTransform sample that does that.

> 
> This is what I tried:
> 
> //Declaration of wrapper class
> XALAN_USING_XALAN(XalanOutputStream)
> class xalan_string_stream:public XalanOutputStream{
>    private:
>           char *output;
>           char *buffer;
>           unsigned cursor;
>    public:
>     xalan_string_stream(MemoryManagerType
>  XALAN_DEFAULT_CONSTRUCTOR_MEMORY_MGR,
>   	size_type theBufferSize = eDefaultBufferSize,
>   	size_type theTranscoderBlockSize = eDefaultTranscoderBlockSize,
>           bool fThrowTranscodeException = true){
>       buffer=new char[1024];
>     }
> 
>     ~xalan_string_stream(){}
> 

In the destructor, you need:

     delete [] buffer;

or you'll have a memory leak;

>     void writeData (const char *input, size_type length){
>       bcopy(input,buffer,length);
>     }
> 

This is extremely dangerous, because you have no guarantee the data will 
fit in the buffer you've allocated.

>     void doFlush (){
>     }
> 
>     char *get_result(){
>       return buffer;
>     }
>  };
> 
> //usage inside main
>         istrstream  theXMLStream(theInputDocument,
>  strlen(theInputDocument));
> 
>         istrstream  theXSLStream(theStyleSheet, strlen(theStyleSheet));
> 
>         XALAN_USING_XALAN(XalanDOMString)
>         XALAN_USING_XALAN(XalanOutputStreamPrintWriter)
>         XALAN_USING_XALAN(XSLTResultTarget)
>         XALAN_USING_XALAN(XSLTInputSource)
> 
>         XSLTInputSource inputSource(&theXSLStream);
> 
>         inputSource.setSystemId(XalanDOMString("foo").c_str());
> 
>         const xalan_string_stream *outputStream = new xalan_string_stream();
> 
>         XalanOutputStreamPrintWriter *printWriter=new
>  XalanOutputStreamPrintWriter((XalanOutputStream &)outputStream, false);
>

Where did you get this cast from?  Are you trying to remove const from 
the xalan_string_stream instance?  Why would you define it const in the 
first place?

This is much simpler:

     xalan_string_stream   outputStream;

     XalanOutputStreamPrintWriter printWriter(&outputStream);

     XSLTResultTarget target(&printWriter);

>         XSLTResultTarget target(printWriter);
> 
>         theResult = theXalanTransformer.transform(&theXMLStream,
>  inputSource,target);
> 
> //compilation error obtained
>  BufferTransform.cpp:40: base `xalanc_1_10::XalanOutputStream' with only
>      non-default constructor in class without a constructor

Well, you have to call the base class constructor, and there's no 
default for the base class.  Perhaps you meant something like this:

XALAN_USING_XALAN(XalanOutputStream)
XALAN_USING_XALAN(XalanMemMgrs)
XALAN_USING_XALAN(MemoryManagerType)

class xalan_string_stream:public XalanOutputStream{
    private:
           char *output;
           char *buffer;
           unsigned cursor;
    public:
     xalan_string_stream(MemoryManagerType&  theMgr
  XALAN_DEFAULT_CONSTRUCTOR_MEMORY_MGR,
   	size_type theBufferSize = eDefaultBufferSize,
   	size_type theTranscoderBlockSize = eDefaultTranscoderBlockSize,
     bool fThrowTranscodeException = true):
         XalanOutputStream(
             theMgr,
             theBufferSize,
             theTranscoderBlockSize,
             fThrowTranscodeException) {
       buffer=new char[1024];
     }
...

>  BufferTransform.cpp:54: ISO C++ forbids defining types within return type
>  BufferTransform.cpp:54: destructors must be member functions
>  BufferTransform.cpp:54: return type specification for destructor invalid
>  BufferTransform.cpp:56: type specifier omitted for parameter `size_type'
>  BufferTransform.cpp:56: syntax error before `)' token
>  BufferTransform.cpp: In function `void writeData(...)':
>  BufferTransform.cpp:57: `input' undeclared (first use this function)
>  BufferTransform.cpp:57: (Each undeclared identifier is reported only once
>  for each function it appears in.)
>  BufferTransform.cpp:57: `buffer' undeclared (first use this function)
>  BufferTransform.cpp:57: `length' undeclared (first use this function)
>  BufferTransform.cpp: At global scope:
>  BufferTransform.cpp:66: syntax error before `}' token
>  BufferTransform.cpp: In function `int transform(const char*, char*)':
>  BufferTransform.cpp:155: ISO C++ forbids declaration of
>  `xalan_string_stream'
>      with no type
>  BufferTransform.cpp:155: uninitialized const `xalan_string_stream'
>  BufferTransform.cpp:155: syntax error before `*' token
>  BufferTransform.cpp:157: `outputStream' undeclared (first use this
>  function)
>  make: *** [all] Error 1
> 

You should not be relying on this list to help you correct C++ syntax 
errors.  Please make sure your code is reasonably correct before you 
post a question.

Dave