Question

我有一个简单的记录器，它实现为单例。当我在linux中使用g ++编译和运行它时它的工作方式就像我想要的那样但是当我使用vc ++在Visual Studio 9.0中编译时，我得到以下错误。有没有办法来解决这个问题？我不介意改变记录器类，但我想避免改变它的调用方式。

1>Linking...
1>loggerTest.obj : error LNK2005: "public: static class Logger * __cdecl Logger::getInstance(void)" (?getInstance@Logger@@SAPAV1@XZ) already defined in Logger.obj
1>loggerTest.obj : error LNK2005: "public: void __thiscall Logger::log(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &)" (?log@Logger@@QAEXABV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z) already defined in Logger.obj
1>loggerTest.obj : error LNK2005: "public: void __thiscall Logger::closeLog(void)" (?closeLog@Logger@@QAEXXZ) already defined in Logger.obj
1>loggerTest.obj : error LNK2005: "private: static class Logger * Logger::_instance" (?_instance@Logger@@0PAV1@A) already defined in Logger.obj
1>Logger.obj : error LNK2001: unresolved external symbol "private: static class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > Logger::_path" (?_path@Logger@@0V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@A)
1>loggerTest.obj : error LNK2001: unresolved external symbol "private: static class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > Logger::_path" (?_path@Logger@@0V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@A)
1>Logger.obj : error LNK2001: unresolved external symbol "private: static class boost::mutex Logger::_mutex" (?_mutex@Logger@@0Vmutex@boost@@A)
1>loggerTest.obj : error LNK2001: unresolved external symbol "private: static class boost::mutex Logger::_mutex" (?_mutex@Logger@@0Vmutex@boost@@A)
1>Logger.obj : error LNK2001: unresolved external symbol "private: static class std::basic_ofstream<char,struct std::char_traits<char> > Logger::_log" (?_log@Logger@@0V?$basic_ofstream@DU?$char_traits@D@std@@@std@@A)
1>loggerTest.obj : error LNK2001: unresolved external symbol "private: static class std::basic_ofstream<char,struct std::char_traits<char> > Logger::_log" (?_log@Logger@@0V?$basic_ofstream@DU?$char_traits@D@std@@@std@@A)

代码，三个文件Logger.h Logger.cpp test.cpp

#ifndef __LOGGER_CPP__
#define __LOGGER_CPP__
#include "Logger.h"

Logger* Logger::_instance = 0;

//string Logger::_path = "log";
//ofstream Logger::_log;
//boost::mutex Logger::_mutex;

Logger* Logger::getInstance(){
  { 
    boost::mutex::scoped_lock lock(_mutex);
    if(_instance == 0) {
      _instance = new Logger;
   _path = "log";
    }
  } //mutex
  return _instance;
}


void Logger::log(const std::string& msg){
  {
    boost::mutex::scoped_lock lock(_mutex);
    if(!_log.is_open()){
      _log.open(_path.c_str());
    }
    if(_log.is_open()){
    _log << msg.c_str() << std::endl;
    }
  }
}

void Logger::closeLog(){
  Logger::_log.close();
}

#endif

`...

#ifndef __LOGGER_H__
#define __LOGGER_H__
#include <iostream>
#include <string>
#include <fstream>
#include <boost/thread/mutex.hpp>
#include <boost/thread.hpp>
using namespace std;

class Logger {
  public:
    static Logger* getInstance();
    void log(const std::string& msg);
    void closeLog();
  protected:
    Logger(){}
  private:
    static Logger* _instance;

    static string _path;
    static bool _logOpen;
    static ofstream _log;
    static boost::mutex _mutex; //check mutable
};
#endif

TEST.CPP `

#include <iostream>
#include "Logger.cpp"
using namespace std;
int main(int argc, char *argv[])
{
  Logger* log = Logger::getInstance();
  log->log("hello world\n");
  return 0;
}

Answer 1

这是一个问题，因为您已经多次通过编译CPP定义了符号，然后将其包含在test.cpp中...按照惯例，您应该只包含声明，而不是<你已经完成了em> definition 。

我很惊讶gcc会让人对此如此松懈。

变化

#include "Logger.cpp"

到

#include "Logger.h"

并尝试一下。

Answer 2

问题是因为您在test.cpp中完成了#include "Logger.cpp"而不是#include "Logger.h"。因此，Logger.cpp中的符号将被定义多次（一次用于转换单元logger.cpp，一次用于test.cpp）。拥有多个包含保护并没有帮助，因为它只能在翻译单元中工作。

vc 9.0中的单例代码链接器错误。在使用gcc编译的linux中运行良好

2 个答案: