Как читать структурную переменную оптом с клавиатуры, которая содержит c-строку, int и float?

Question

#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; 
} 

Это дает мне полный экран ошибок. Кто-нибудь знает, как решить эту проблему? Спасибо!

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]

Answer 1

Создать friend функцию перегружают:

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

Вот что программа будет выглядеть следующим образом:

#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

Answer 2

Это не происходит автоматически, потому что std::cin не имеет ни малейшего представления о том, как вы ожидаете, вход должен быть отформатирован или как вход должен быть назначен на членов news объекта. Вы должны будете прочитать в каждый из его членов в отдельности:

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

Вы можете альтернативно предоставить operator>> перегрузку news, осуществившего что-то вроде этого. Например:

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