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Redirecting CLI output in a c++ QT app.

Posted on 2010-11-10
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Last Modified: 2012-05-10
HI Guys,
I'm trying to redirect all stdout to a text box in my QT 4 app.  I found the following code in a forum and other people said it worked.  My problem is that I'm new to c++ and cant figure out the following compiler error message.  Any input would be appriciated.

 error: ‘myRedirector’ was not declared in this scope
freeems_loader.cpp:29: error: no matching function for call to ‘StdRedirector<char, std::char_traits<char> >::StdRedirector(std::ostream&, <unresolved overloaded function type>, QTextBrowser*&)’
freeems_LoaderRedirector.h:29: note: candidates are: StdRedirector<Elem, Tr>::StdRedirector(std::ostream&, void (*)(const Elem*, std::streamsize, void*), void*) [with Elem = char, Tr = std::char_traits<char>]
freeems_LoaderRedirector.h:16: note:                 StdRedirector<char, std::char_traits<char> >::StdRedirector(const StdRedirector<char, std::char_traits<char> >&)
freeems_loader.cpp:33: warning: the address of ‘QTextStream& endl(QTextStream&)’ will always evaluate as ‘true’
make[1]: *** [debug/freeems_loader.o] Error 1
make: *** [debug] Error 2
#ifndef FREEEMS_LOADERREDIRECTOR_H_

#define FREEEMS_LOADERREDIRECTOR_H_





#endif /* FREEEMS_LOADERREDIRECTOR_H_ */



template< class Elem = char, class Tr = std::char_traits< Elem > >

  class StdRedirector : public std::basic_streambuf< Elem, Tr >

  {

      /**

        * Callback Function.

        */

    typedef void (*pfncb) ( const Elem*, std::streamsize _Count, void* pUsrData );



  public:

      /**

        * Constructor.

        * @param a_Stream the stream to redirect

        * @param a_Cb the callback function

        * @param a_pUsrData user data passed to callback

        */

    StdRedirector( std::ostream& a_Stream, pfncb a_Cb, void* a_pUsrData ) :

      m_Stream( a_Stream ),

      m_pCbFunc( a_Cb ),

      m_pUserData( a_pUsrData )

    {

        //redirect stream

      m_pBuf = m_Stream.rdbuf( this );

    };



      /**

        * Destructor.

        * Restores the original stream.

        */

    ~StdRedirector()

    {

      m_Stream.rdbuf( m_pBuf );

    }



      /**

        * Override xsputn and make it forward data to the callback function.

        */

    std::streamsize xsputn( const Elem* _Ptr, std::streamsize _Count )

    {

      m_pCbFunc( _Ptr, _Count, m_pUserData );

      return _Count;

    }



      /**

        * Override overflow and make it forward data to the callback function.

        */

    typename Tr::int_type overflow( typename Tr::int_type v )

    {

      Elem ch = Tr::to_char_type( v );

      m_pCbFunc( &ch, 1, m_pUserData );

      return Tr::not_eof( v );

    }



 protected:

    std::basic_ostream<Elem, Tr>& m_Stream;

    std::streambuf*               m_pBuf;

    pfncb                         m_pCbFunc;

    void*                         m_pUserData;

  };

#########################################################



#include "freeems_LoaderRedirector.h"



a function in my QT GUI class



void FreeEMS_Loader::redirectCLI()

{

	myRedirector = new StdRedirector <>(std::cout,   outCallBack, ui.textOutput);



	std::cout <<"Hello! We are ready" << endl;

}

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Question by:sean-keys
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9 Comments
 
LVL 86

Expert Comment

by:jkr
Comment Utility
Well, the declaration is missing and the call to 'new' also seems to be missing its template argument - did you mean the following?
void FreeEMS_Loader::redirectCLI()

{

	StdRedirector`* myRedirector = new StdRedirector <char>(std::cout,   outCallBack, ui.textOutput);



	std::cout <<"Hello! We are ready" << endl;

}

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LVL 86

Expert Comment

by:jkr
Comment Utility
Ooops, typo, that should be
void FreeEMS_Loader::redirectCLI()

{

	StdRedirector* myRedirector = new StdRedirector <char>(std::cout,   outCallBack, ui.textOutput);



	std::cout <<"Hello! We are ready" << endl;

}

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Author Comment

by:sean-keys
Comment Utility
Now I get a different error, thanks for the fast response.

 missing template arguments before ‘*’ token
freeems_loader.cpp:29: error: ‘myRedirector’ was not declared in this scope
freeems_loader.cpp:29: error: no matching function for call to ‘StdRedirector<char, std::char_traits<char> >::StdRedirector(std::ostream&, <unresolved overloaded function type>, QTextBrowser*&)’
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LVL 86

Expert Comment

by:jkr
Comment Utility
Argh, my bad, not a good idea to mention the template argument and then omitting it again - try
void FreeEMS_Loader::redirectCLI()

{

	StdRedirector<char>* myRedirector = new StdRedirector <char>(std::cout,   outCallBack, ui.textOutput);



	std::cout <<"Hello! We are ready" << endl;

}

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Author Comment

by:sean-keys
Comment Utility
Getting closer, I apologize for my ignorance.    

 error: no matching function for call to ‘StdRedirector<char, std::char_traits<char> >::StdRedirector(std::ostream&, <unresolved overloaded function type>, QTextBrowser*&)’
freeems_LoaderRedirector.h:29: note: candidates are: StdRedirector<Elem, Tr>::StdRedirector(std::ostream&, void (*)(const Elem*, std::streamsize, void*), void*) [with Elem = char, Tr = std::char_traits<char>]
freeems_LoaderRedirector.h:16: note:                 StdRedirector<char, std::char_traits<char> >::StdRedirector(const StdRedirector<char, std::char_traits<char> >&)
freeems_loader.cpp:35: warning: the address of ‘QTextStream& endl(QTextStream&)’ will always evaluate as ‘true’
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Expert Comment

by:jkr
Comment Utility
How is 'outCallBack' declared?
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Author Comment

by:sean-keys
Comment Utility

void FreeEMS_Loader::outCallBack( const char* ptr, std::streamsize count, void* pTextBox )
{
  (void) count;
  QTextBrowser* p = static_cast< QTextBrowser* >( pTextBox );
  p->append( ptr );
}
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Accepted Solution

by:
jkr earned 500 total points
Comment Utility
Well, that seems to be the problem, you can't use a member function here - can you make that a static member and make the call look like
void FreeEMS_Loader::redirectCLI()

{

	StdRedirector<char>* myRedirector = new StdRedirector <char>(std::cout,   (StdRedirector<char>::pfncb) outCallBack, ui.textOutput);



	std::cout <<"Hello! We are ready" << endl;

}

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Author Closing Comment

by:sean-keys
Comment Utility
Thanks!
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