我提供了下面的代码。当我重载重载的后缀运算符时,编译器会抛出错误。它适用于重载的前缀运算符。错误
error: no match for ‘operator<<’ in ‘std::cout << cDigit.Digit::operator++(0)’
代码
#include <iostream>
using namespace std;
class Digit
{
private:
int m_nDigit;
public:
Digit(int nDigit=0)
{
m_nDigit = nDigit;
}
Digit& operator++(); // prefix
Digit& operator--(); // prefix
Digit operator++(int); // postfix
Digit operator--(int); // postfix
friend ostream& operator<< (ostream &out, Digit &digit);
int GetDigit() const { return m_nDigit; }
};
Digit& Digit::operator++()
{
// If our number is already at 9, wrap around to 0
if (m_nDigit == 9)
m_nDigit = 0;
// otherwise just increment to next number
else
++m_nDigit;
return *this;
}
Digit& Digit::operator--()
{
// If our number is already at 0, wrap around to 9
if (m_nDigit == 0)
m_nDigit = 9;
// otherwise just decrement to next number
else
--m_nDigit;
return *this;
}
Digit Digit::operator++(int)
{
// Create a temporary variable with our current digit
Digit cResult(m_nDigit);
// Use prefix operator to increment this digit
++(*this); // apply operator
// return temporary result
return cResult; // return saved state
}
Digit Digit::operator--(int)
{
// Create a temporary variable with our current digit
Digit cResult(m_nDigit);
// Use prefix operator to increment this digit
--(*this); // apply operator
// return temporary result
return cResult; // return saved state
}
ostream& operator<< (ostream &out, Digit &digit)
{
out << digit.m_nDigit;
return out;
}
int main()
{
Digit cDigit(5);
cout << ++cDigit << endl; // calls Digit::operator++();
cout << --cDigit << endl; // calls Digit::operator--();
cout << cDigit++ << endl; // calls Digit::operator++(int); //<- Error here??
return 0;
}
最佳答案
你的 operator<<
应该取它的Digit
常量引用的参数:
ostream& operator<< (ostream &out, const Digit &digit)
这里需要这个因为Digit::operator++(int)
返回一个临时对象,该对象不能传递给采用非常量引用的函数。
关于c++ - ostream 运算符在重载的后缀增量/减量运算符上重载,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/9928121/