CODEWITHSUNDEEP
c++overloading
HRLTY
HRLTY

Reputation: 74

Why overloaded operator << works sometimes but other times doesn't

I don't know why cout << da << '\n' works fine,but std::cout << next_Monday(da) << '\n' went wrong. Why the direct Date object can output, but the return Date can't. Why overloaded operator << works sometimes but other times doesn't. here is my code.. 

#include <iostream>
#include <stdlib.h>

struct Date {
    unsigned day_: 5;
    unsigned month_ : 4;
    int year_: 15;
};

std::ostream& operator<<(std::ostream& out,Date& b)
{
    out << b.month_ << '/' << b.day_ << '/' << b.year_;
    return out;
}

std::istream& operator>>(std::istream& in,Date& b);
Date next_Monday(Date const &d);

int main()
{
    Date da;
    std::cin >> da;
    std::cout << da << '\n';
    std::cout << next_Monday(da) << '\n';
    return 0;
}

this is what clang said: (I use g++ to invoke)

excercise19DateManipulate.cpp:114:18: error: invalid operands to binary expression ('ostream' (aka 'basic_ostream<char>') and 'Date') std::cout<< next_Monday(da) <<'\n'; ~~~~~~~~^ ~~~~~~~~~~~~~~~

Upvotes: 2

Views: 103

Answers (2)

Richard Allan
Richard Allan

Reputation: 1

You never defined the "next_Monday()" function as far as I can see, you only declared it.

Upvotes: -2

juanchopanza
juanchopanza

Reputation: 227370

Because you can't bind a temporary to a non-const lvalue reference. Change the operator to take a const reference:

std::ostream& operator<<(std::ostream& out, const Date& b)

Upvotes: 6

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