Hi,

I am totally new to C++ and I'm trying to create a simple program using Visual Studio 2005. I'm using win32 console project.

The idea is I have a class inside of a namespace declared on a .h file. The definition of the class is on a .cpp file.
The problem is the defined template function is not being recognized on link stage. But when the template function:

template< class T >
      int write( const T& pObj, bool LogState = true,
                 std::streamsize precision = 2,
                 std::ios_base::fmtflags iosFlags = std::ios::fixed
               );

is defined inline on the .h file, it works well.

Please help me with this.. I anticipate any form of help.

Please bear with my spaghetti code here:


//Logger.cpp
#include "incs.h"

namespace log
{
  Logger::Logger()
  {
    try
    {
        LogFileName = "EventHistory.log";
        LogFile.open( LogFileName.c_str(), std::ios::app );
    }
    catch(std::ios_base::failure& )
    {
        //std::cout<<"Error: "<<e.what()<<std::endl;
      throw; //throw exception to outer level error handler
    }
  }

  Logger::Logger( const std::string& filename )
  {
    try
    {
        LogFile.open( filename.c_str(), std::ios::app );
    }
    catch( std::ios_base::failure& )
    {
      throw;
    }
  }

  Logger::~Logger()
  {
    try
    {
        LogFile.flush();
        LogFile.close();
    }
    catch( std::ios_base::failure& )
    {
      throw;
    }
  }

  template< class T > int Logger::write( const T& pObj , bool LogState,
                                              std::streamsize precision,
                                              std::ios_base::fmtflags iosFlags )
  {

    if( LogState)
    {
        LogFile<<std::endl;
        LogFile<<"Date: "<<__DATE__<<std::endl;
        LogFile<<"File: "<<__FILE__<<std::endl;
        LogFile<<"Time: "<<__TIME__<<std::endl;

      LogFile<<std::setiosflags( iosFlags );
      LogFile<<std::setprecision( precision );

        LogFile<<"Activity: "<<pObj<<std::endl;
      }

      return 0;
  }
}


//Logger.h

#ifndef __LOGGER_H__
#define __LOGGER_H__

namespace log
{
    class Logger
    {
      private:
          std::ofstream LogFile;
          std::string LogFileName;

      //protected:

      public:
          Logger();
          Logger( const std::string& filename );
          ~Logger();

      template< class T >
      int write( const T& pObj, bool LogState = true,
                 std::streamsize precision = 2,
                 std::ios_base::fmtflags iosFlags = std::ios::fixed
               );

  };
}

#endif


//LoggerTester.cpp

#include "incs.h"
#include "Logger.h"

using namespace log;

int main( int argc, char*argv[] )
{
  try
  {
    Logger EventLog;
      char ch = 'C';

      EventLog.write( ch );
      EventLog.write<std::string>("This string will be logged.");
    EventLog.write<float>(10.50);

    try
    {
      EventLog.write('T',true );
      EventLog.write("Another string to be logged.", std::ios_base::fixed );
      EventLog.write(500.7621, true, 4, std::ios::fixed );

      EventLog.write("This string won't be written on the log.", false );
    }
    catch( std::ios_base::failure& )
    {
      throw;
    }
  }
  catch( std::ios_base::failure& e )
  {
    std::cout<<"Error: "<<e.what()<<std::endl;
  }

  try
  {
    Logger EventLog( "EventHistory2.log" );
    EventLog.write("Writing events to event logger.");
  }
  catch( std::ios_base::failure& e )
  {
    std::cout<<"Error: "<<e.what()<<std::endl;
  }

    return 0;
}


//incs.h

//standard libraries
#include <iostream>
#include <exception>
#include <string>
#include <iomanip>
#include <fstream>


//defined headers
#include "Logger.h"




Linker result:
LoggerTester.obj : error LNK2019: unresolved external symbol "public: int __thiscall log::Logger::write<char const [32]>(char const (&)[32],bool,int,int)" (??$write@$$BY0CA@$$CBD@Logger@log@@QAEHAAY0CA@$$C BD_NHH@Z) referenced in function __catch$_main$0
LoggerTester.obj : error LNK2019: unresolved external symbol "public: int __thiscall log::Logger::write<char const [41]>(char const (&)[41],bool,int,int)" (??$write@$$BY0CJ@$$CBD@Logger@log@@QAEHAAY0CJ@$$C BD_NHH@Z) referenced in function _main
LoggerTester.obj : error LNK2019: unresolved external symbol "public: int __thiscall log::Logger::write<double>(double const &,bool,int,int)" (??$write@N@Logger@log@@QAEHABN_NHH@Z) referenced in function _main
LoggerTester.obj : error LNK2019: unresolved external symbol "public: int __thiscall log::Logger::write<char const [29]>(char const (&)[29],bool,int,int)" (??$write@$$BY0BN@$$CBD@Logger@log@@QAEHAAY0BN@$$C BD_NHH@Z) referenced in function _main
LoggerTester.obj : error LNK2019: unresolved external symbol "public: int __thiscall log::Logger::write<float>(float const &,bool,int,int)" (??$write@M@Logger@log@@QAEHABM_NHH@Z) referenced in function _main
LoggerTester.obj : error LNK2019: unresolved external symbol "public: int __thiscall log::Logger::write<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,bool,int,int)" (??$write@V?$basic_string@DU?$char_traits@D@std@@V ?$allocator@D@2@@std@@@Logger@log@@QAEHABV?$basic_ string@DU?$char_traits@D@std@@V?$allocator@D@2@@st d@@_NHH@Z) referenced in function _main
LoggerTester.obj : error LNK2019: unresolved external symbol "public: int __thiscall log::Logger::write<char>(char const &,bool,int,int)" (??$write@D@Logger@log@@QAEHABD_NHH@Z) referenced in function _main
D:\development\course\development\ANSI C++\miscellaneous\Activity File Logger\Debug\Activity File Logger.exe : fatal error LNK1120: 7 unresolved externals

&lt;bizz&gt;

Try using Google - it gives 94,000 entries for "LNK1120 error"

such as - http://www.kbalertz.com/kb_909350.aspx
and - http://support.microsoft.com/default...b;en-us;815650

Also find Microsoft Knowledge Base (use Google again) and get familiar with it if you are using Microsoft products.

If you get yourself familiar with search techniques you can save yourself a lot of time.

Alan