类构造函数"C2248:'std :: basic_ios <_Elem,_Traits> :: basic_ios':无法访问类'std :: basic_ios <_Elem,_Traits>中声明的私有成员"

Question

这是我的第一篇文章.

我阅读了很多主题,似乎我做得很好,但是当我尝试编译以下代码时,我再次遇到上述错误:

// Header file

#include <fstream>
#include <ostream>
#include <string>

using namespace std;

class CLogger
{
private:
    ostream m_oStream;

public:
    CLogger(ostream& oStream);
    CLogger(const string sFileName);
};

// Implementation file

CLogger::CLogger(ostream& oStream) : 
m_oStream(oStream) // <-- Here is the problem?!
{
}

CLogger::CLogger(const string sFileName) :
    m_oStream(ofstream(sFileName.c_str()))
{   
}

你可以帮帮我吗？

非常感谢你!

Answer 1

CLogger::CLogger(ostream& oStream) : // <-- Here is the problem?!
m_oStream(oStream)

问题不在第一行,而是在第二行.

由于成员m_oStream被声明为非引用,因此上面的第二行尝试复制oStream哪一个是不可能的,因为复制构造函数std::ostream是通过创建它private而禁用的,这是您在错误消息中看到的"无法访问私有会员."

修复是这样的:

std::ostream * m_oStream; //declare it as pointer.
bool m_deleteStream;      //flag whether to delete m_oStream or not

现在这样做:

CLogger::CLogger(ostream& oStream) : 
m_oStream(&oStream), m_deleteStream(false)
{
}

CLogger::CLogger(const string sFileName) :
m_oStream(new std::ofstream(sFileName)), m_deleteStream(true)
{
  //Note : in C++03, you've to pass sFileName.c_str() to 
  //the constructor of std::ostream   
}

然后你要把析构函数写成:

~CLogger()
 {
    if ( m_deleteStream )
    {
        delete m_oStream;
    }
 }

重要的一点是:由于这是一个资源管理(记录器)类,因此将其设置为不可复制是一个好主意,因为复制对记录器实例没有意义.