c++ - 错误 C2248 : 'std::basic_ios<_Elem,_Traits>::basic_ios' : cannot access private member declared in class 'std::basic_ios<_Elem,_Traits>'

Question

收到此错误，我很确定它在 operator<< 函数中。两份打印品都是公开的。

void CRational::print() const
{
    print(cout);
}

void CRational::print(ostream & sout) const
{
    if(m_denominator == 1)
        cout << m_numerator;
    else
        cout << m_numerator << "/" << m_denominator;
}

ostream operator<<(ostream & sout,const CRational a)
{
    a.print();

    return sout;
}

CRational operator++() // prefix ++x
{
    m_numerator += m_denominator;
    return *this;
}

in main:
cout << "e before: " << e << ", \"cout << ++e\" : " << ++e << " after: " << e << endl; 

Answer 1

您需要通过引用而不是值返回 ostream。它试图调用构造函数。也可以传递 'a' 作为引用:

ostream& operator<<(ostream & sout,const CRational& a)

我还注意到打印方法可能是错误的。它有 sout 作为流的名称传递，但随后直接使用 cout 实现。应该是

void CRational::print(ostream & sout) const
{
    if(m_denominator == 1)
        sout << m_numerator;
    else
        sout << m_numerator << "/" << m_denominator;
}