为什么cin在包含String标头后接受字符串输入

Question

I am new to C++ programming. I was trying to take user inputs and put them in a variable and i was using cin . It was working for integer's and other's except strings . So, when I searched around I found that I have to include <string> header. I just want to understand, what changes occurred by including string header? I thought that cin is overloaded by a function defined in the string header. So, I started looking into string header and I could not find cin overloaded or any function defined there at all. Can any one tell me how cin started accepting string inputs after including <string> ?

Answer 1

<string> defines the functions

template <class CharT, class Traits, class Allocator>
std::basic_ostream<CharT, Traits>& 
    operator<<(std::basic_ostream<CharT, Traits>& os, 
               const std::basic_string<CharT, Traits, Allocator>& str);

template <class CharT, class Traits, class Allocator>
std::basic_istream<CharT, Traits>& 
    operator>>(std::basic_istream<CharT, Traits>& is, 
               std::basic_string<CharT, Traits, Allocator>& str);

These free, standard library functions, are what allows you to use a std::string with any stream that is or is derived from a basic_ostream or basic_istream .

Answer 2

The <string> header mainly defines the standard library's std::string class. Without it, you have no string class in C++: It's not integral to the language. Of course you could use char* -strings, C-style, but that's not how we typically do things in C++.

Along with std::string , that header also defines >> and << operators for std::string 's and streams, so that you can do things like std::cout << my_string and std::cin >> another_string . That syntax is equivalent to operator<<(std::cout, my_string) and operator>>(std::cin, another_string) .

Important note: The C language's <string.h> header is completely different than C++'s <string> . The C language header is usable just like it is in C, and defines certain functions working on char* (null-terminated) strings . Don't confuse the two headers, nor the two kinds of "strings".