链接器错误LNK2019

Question

I have been playing around with Template functions, and made a little logger program. I have been trying to split this into header / source file, but I keep getting linker errors. I know this is simple, but I cant figure it out.

Also I have some convince vars in the logger header, where would be the "proper" place for those? (logStart, logEnd etc.)

All code below.

Header

#ifndef __moot_logger_hpp__
#define __moot_logger_hpp__


#include <iostream>
#include <fstream>
#include <string>

using std::ios;

namespace Moot
{
    struct Logger
    {
        Logger();
        ~Logger() {}


        template <class T>      
        void saveToFile(T type);

        template <typename T>
        Logger& operator<< (T type);


        /*
        Logger& operator<< (std::wstring wideStr)
        {
            saveToFile(Moot::convertWstringToString(wideStr));
            return *this;
        }
        */
    };


    /*
    namespace {
        Logger logStart;
        Logger& lStart = logStart;

        const char  logEnd = '\n';
        const char& lEnd   = logEnd;

        const char  logSpace = ' ';
        const char& lSpace   = logSpace;
    }
    */

}


#endif

Source

#include <Moot/logger.hpp>

Moot::Logger::Logger()
{
    std::ofstream logfile;
    logfile.open ("logfile.txt", ios::trunc);
    logfile << "LogFile - most recent at the bottom\n";
    logfile << "-----------------------------------\n \n";
    logfile.close();
}


template <typename T>
void Moot::Logger::saveToFile(T type)
{
    std::ofstream logfile;
    logfile.open ("logfile.txt", ios::in | ios::app);
    logfile << type;
    logfile.close();
}


template <typename T>
Moot::Logger& Moot::Logger::operator<< (T type) 
{
    saveToFile(type);
    return *this;
}


/*
Logger::Logger& operator<< (std::wstring wideStr)
{
    saveToFile(Moot::convertWstringToString(wideStr));
    return *this;
}
*/

main

#include <Moot/logger.hpp>
#include <iostream>

int main()
{
    std::cout << "hello" << std::endl;

    Moot::Logger() << 12;
    //Moot::lStart.saveToFile(23);
    //Moot::lStart.operator << 13;

    return 0;
};

Answer 1

You'll want to read the C++ FAQ Lite question, "Why can't I separate the definition of my templates class from its declaration and put it inside a .cpp file?"

Effectively, you need to define your function and class templates in the header file, not in the .cpp file.

Answer 2

如果你想要从模板类的声明中划分除定义而不是使用hpp或tpp将文件移动到单独的文件（tpp并不总是由文本编辑器正确处理）扩展并在声明文件的末尾添加定义文件的include指令