C ++运算符重载错误：'is >>“（“'中的'operator >>'不匹配

Question

I'm trying to learn operator overloading and I got an error on my first attempt.

template<typename T>
class Pair
{
public:
    T x; T y;
    Pair(T x, T y): x(x), y(y){};
    ~Pair(){};

    /* data */
};
template<typename T>
ostream& operator<<(ostream &os, const Pair<T> &p)
{
    return os<<"("<<p.x<<", "<<p.y<<")";
}

template<typename T>
istream& operator>>(istream &is, Pair<T> &p)
{
    return is>>"(">>p.x>>", ">>p.y>>")";
}

I want to be able to do the following:

Pair<int> p;
cin>>p;
cout<<p;

And giving input for Pair object means being able to give (1, 2) as input which after cin , produces a Pair<int> .

I get a compile time error at is>>"(" . What is the way to correct this?

Answer 1

return is>>"(">>p.x>>", ">>p.y>>")";

is nonsense: you are trying to move the information of the stream 'is' into the constant string ")". I think what you want is this:

template<typename T>
istream& operator>>(istream &is, Pair<T> &p)
{
   is.seekg(1, std::ios::cur); // skip 1 char, "("
   is >> p.x;
   is.seekg(2, std::ios::cur); // skip 2 chars, ", "
   is >> p.y;
   is.seekg(1, std::ios::cur); // skip 1 char, ")"
}

Answer 2

You are trying to read into string literals "(" and ")" . You cannot do that.

Try this:

template<typename T>
istream& operator>>(istream &is, Pair<T> &p)
{
    return is >> p.x>> p.y;
}

Answer 3

As others have pointed out, you're trying to read into literals in the extractor. I'd suggest fixing this by reading a char first and comparing it with '(' . You signal an error if that fails, otherwise extract T and repeat the process.

In code:

template <typename T>
istream& operator>> (istream &is, Pair<T> &p)
{
  char c;
  if (!(is >> c)) return is;
  if (c != '(') {
    is.setstate(is.failbit);
    return is;
  }
  if (!(is >> p.x >> c)) return is;
  if (c != ',') {
    is.setstate(is.failbit);
    return is;
  }
  if (!(is >> p.x >> c)) return is;
  if (c != ')') {
    is.setstate(is.failbit);
  }
  return is;
}

Answer 4

您不必在输入运算符重载中读取“（”字符串文字，只需读取px和py。