C++ class redefinition error

I am compiling a logging program, but I am receiving this error and cant figure it out for the life of me...

logger.cpp:15: error: redefinition of ‘class Logger’
logger.h:20: error: previous definition of ‘class Logger’

with gcc when i compile with

g++ -Wall logger.cpp -o log

logger.h:

#ifndef LOGGER_H
#define LOGGER_H

#include <fstream>
#include <iostream>
#include <string>
using std::string;

class Logger
{

static Logger* m_pInstance;

public:
static Logger* Instance() { return m_pInstance; }
void writeLog(string message);
void openLogFile(string fileName);
void closeLogFile();
void deleteLogger();

};
#endif

logger.cpp

#include "logger.h"

#include <fstream>
#include <iostream>

class Logger
{
static Logger* m_pInstance;
std::ofstream m_开发者_JAVA技巧pOutputFile;
Logger()
{
}
~Logger()
{
}

public:
static Logger* Instance()
{
    if(!m_pInstance)
    {
        m_pInstance = new Logger;
    }
    return m_pInstance;
}
void writeLog(std::string message)
{
    m_pOutputFile << message << "\n";
    std::cout << "you just wrote  " << message << "  to the log file!\n" << std::endl;
}
void openLogFile(std::string fileName)
{
    m_pOutputFile.open(fileName.c_str(),std::ios::out);
}
void closeLogFile()
{
    m_pOutputFile.close();
}
void deleteLogger()
{
    delete m_pInstance;
}
};
Logger* Logger::m_pInstance = NULL;

It's exactly what the error message says. The implementation file can't just provide a redefinition of the class adding new member variables and conflicting function bodies wherever it pleases. Instead, provide definitions for the functions and static member variables you've already declared.

#include "logger.h"

#include <fstream>
#include <iostream>


static Logger::Logger* m_pInstance;

Logger::Logger()
{
}

Logger::~Logger()
{
}

// this also is illegal, there's a body provided in the header file
//Logger* Logger::Instance()
//{
//    if(!m_pInstance)
//    {
//        m_pInstance = new Logger;
//    }
//    return m_pInstance;
//}

void Logger::writeLog(std::string message)
{
    m_pOutputFile << message << "\n";
    std::cout << "you just wrote  " << message << "  to the log file!\n" << std::endl;
}

and so on

Well, because you are redefining the class. You can't say 'class Logger {' again in the .cpp when you already included it from the .h.

Compiler always expects only one class definition in the whole namespace(or scope) that class belongs to. Currently in the code you specified, you would see that there are infact 2 class definitions: one in .h file and another one in .cpp file. That is why the compiler is complaining that you are redefining a class which is not allowed.

Generally whenever you encounter a compiler error, it's a good idea to look at the lines that compiler tells. Most of the time the problem is in the line the compiler points out.