C++类重定义错误

Question

我正在编译一个日志记录程序,但是我收到了这个错误,并且无法解决我的生活...

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

用gcc编译时

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_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;

Answer 1

这正是错误消息所说的内容.实现文件不仅可以提供类的重新定义,还可以在任何地方添加新的成员变量和冲突的函数体.相反,为已经声明的函数和静态成员变量提供定义.

#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;
}

等等