以下尝试运算符重载导致错误:
#include<iostream>
#include<string>
#include<ostream>
using namespace std;
class Dollar
{
private:
float currency, mktrate, offrate;
public:
Dollar(float);
float getDollar() const;
float getMarketSoums() const;
float getofficialSoums() const;
void getRates();
// In the following function I was trying to overload "<<" in order to print all the data members:
friend void operator<<(Dollar &dol, ostream &out)
{
out << dol.getDollar() << endl;
out << dol.getMarketSoums() << endl;
out << dol.getofficialSoums() << endl;
}
};
Dollar::Dollar(float d)
{
currency = d;
}
float Dollar::getDollar() const
{
return currency;
}
float Dollar::getMarketSoums() const
{
return mktrate;
}
float Dollar::getofficialSoums() const
{
return offrate;
}
void Dollar::getRates()
{
cin >> mktrate;
cin >> offrate;
}
int main()
{
Dollar dollar(100);
dollar.getRates();
// In this line I am getting the error. Could you please help to modify it correctly?
cout << dollar;
system("pause");
return 0;
}
答案 0 :(得分:4)
您必须将std::ostream
对象作为第一个参数传递给插入运算符<<
而不是第二个参数,只要您以这种方式调用它:
friend void operator << (ostream &out, Dollar &dol);
只要此函数仅打印并且不打算修改对象的成员,就应该将对象传入插入操作符constant reference
:
friend void operator << (ostream &out, const Dollar& dol);
因此,通过引用传递以避免多个副本和const
以避免意外修改。
如果你想调用它以你想要的方式工作,你可以这样做:
friend void operator<<(const Dollar &dol, ostream &out){
out << dol.getDollar() << endl;
out << dol.getMarketSoums() << endl;
out << dol.getofficialSoums() << endl;
}
以主要为例:
operator << (dollar, cout); // this is ok
dollar << cout; // or this. also ok.
正如您所看到的,我颠倒了调用插入运算符以匹配上述签名的顺序。但我不建议这样做,只是要了解它应该如何运作。