How to read a structure variable wholesale from keyboard which contains a c-string, an int and a float?

1
votes
#include <iostream>
#include <cmath>
#include <cstdlib>
#include <climits>
#include <cfloat>
#include <cstring>
#include <string>
using namespace std;

struct news
{
    char a[10];
    int n;
    float r;
};

int main()
{
    news k;
    cin >> k;
    cout << k.a << endl;
    cout << k.n << endl;
    cout << k.r << endl;
    return 0;
}

It gives me a full screen of errors. Anybody knows how to solve this problem? Thank you!

test.cc: In function ‘int main()’: test.cc:20: error: no match for ‘operator>>’ in ‘std::cin >> k’ /usr/include/c++/4.2.1/istream:131: note: candidates are: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>& (*)(std::basic_istream<_CharT, _Traits>&)) [with _CharT = char, _Traits = std::char_traits] /usr/include/c++/4.2.1/istream:135: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_ios<_CharT, _Traits>& (*)(std::basic_ios<_CharT, _Traits>&)) [with _CharT = char, _Traits = std::char_traits] /usr/include/c++/4.2.1/istream:142: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(std::ios_base& (*)(std::ios_base&)) [with _CharT = char, _Traits = std::char_traits] /usr/include/c++/4.2.1/istream:178: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(bool&) [with _CharT = char, _Traits = std::char_traits] /usr/include/c++/4.2.1/istream:182: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(short int&) [with _CharT = char, _Traits = std::char_traits] /usr/include/c++/4.2.1/istream:185: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(short unsigned int&) [with _CharT = char, _Traits = std::char_traits] /usr/include/c++/4.2.1/istream:189: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(int&) [with _CharT = char, _Traits = std::char_traits] /usr/include/c++/4.2.1/istream:192: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(unsigned int&) [with _CharT = char, _Traits = std::char_traits] /usr/include/c++/4.2.1/istream:196: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(long int&) [with _CharT = char, _Traits = std::char_traits] /usr/include/c++/4.2.1/istream:200: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(long unsigned int&) [with _CharT = char, _Traits = std::char_traits] /usr/include/c++/4.2.1/istream:205: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(long long int&) [with _CharT = char, _Traits = std::char_traits] /usr/include/c++/4.2.1/istream:209: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(long long unsigned int&) [with _CharT = char, _Traits = std::char_traits] /usr/include/c++/4.2.1/istream:214: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(float&) [with _CharT = char, _Traits = std::char_traits] /usr/include/c++/4.2.1/istream:218: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(double&) [with _CharT = char, _Traits = std::char_traits] /usr/include/c++/4.2.1/istream:222: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(long double&) [with _CharT = char, _Traits = std::char_traits] /usr/include/c++/4.2.1/istream:226: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(void*&) [with _CharT = char, _Traits = std::char_traits] /usr/include/c++/4.2.1/istream:250: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_streambuf<_CharT, _Traits>*) [with _CharT = char, _Traits = std::char_traits]

2
c++structureoutput

2 Answers

4
votes

Create a friend function overload:

friend std::istream& operator >>(std::istream& is, news const& n)
{
    return in >> n.a >> n.n >> n.r;
}

Here's what you program would look like:

#include <iostream>

struct news
{
    char a[10];
    int n;
    float r;

    friend std::istream& operator >>(std::istream& is, news& n)
    {
        return is >> n.a >> n.n >> n.r;
    }
};

int main()
{
    news k;

    std::cin >> k;
    std::cout << k.a << std::endl;
    std::cout << k.n << std::endl;
    std::cout << k.r << std::endl;
}

Live Demo

3
votes

This doesn't happen automatically because std::cin has no idea how you expect the input to be formatted or how the input should be assigned to the members of a news object. You will have to read into each of its members individually:

cin >> k.a >> k.n >> k.r;

You could alternatively provide an operator>> overload for news that performed something like this. For example:

istream& operator>>(istream& in, news& cPoint)
{
  in >> k.a >> k.n >> k.r;
  return in;
}