why std::cin doesn't give error on "char"

Question

Here is a small code:

char a;
while(std::cin >> a) {
    std::cout << a << " is pressed\n";
}

When I type in "w", i get "w is pressed". When I type in "www", i get "w is pressed" 3 times in a row.

Can someone please explain why this happens?

Thanks

because its a string. But then I understand that it kind of does `std::cin >> a >> a >> a;`. How can I change that? — Gasim, Nov 25 '13 at 22:25
**WHAT** do you want to achieve/expect `std::cin` to behave?? This might turn out to be different from reality (i.e. how `std::istream` actually behaves) ... — πάντα ῥεῖ, Nov 25 '13 at 22:33

score 4 · Answer 1 · answered Nov 25 '13 at 22:22

4

When you use std::cin to read a char variable it reads one character at a time. That is why you get 3 iterations in the while loop for input www.

answered Nov 25 '13 at 22:22

Paul92

8,827
1
23
37

@Gasim don't use a while if you just want one input – Hanlet Escaño Nov 25 '13 at 22:26
well, then I should use string with this knowing it will works, right? – Gasim Nov 25 '13 at 22:28
1

@Gasim _'well, then I should use string ...'_ **No!** Looks like, you'll want to process key-pressed events, instead of processing streamed input (from keyboard, file, socket connection, whatever). – πάντα ῥεῖ Nov 25 '13 at 22:58

score 0 · Answer 2 · answered Nov 25 '13 at 22:24

0

There is a queue of inputs. if you entered too much, your input waits in patient...

answered Nov 25 '13 at 22:24

MeNa

1,467
9
23

how can I clear the queue them? right after the first character then – Gasim Nov 25 '13 at 22:26
no luck; i just inputted std::string to cin and got the character by string.at(0) – Gasim Nov 25 '13 at 22:30

score 0 · Answer 3 · answered Nov 25 '13 at 22:42

The first part of the answer is on the first line of your code.

char a;

Variable a is a single char, an 8-bit value typically used to store a code representing a display character. If the display is ASCII, then (value) 0 = no character, (value) 32 = space, value 48 = (character) '0', etc.

std::cin is an instance of class std::istream, it has various members and operator overloads to deal with different types. In the case of a char, you are calling

std::istream::operator(char)

Which reads one char, exactly one, from the input stream and returns.

#include <iostream>
int main()
{
    char a, b, c;
    std::cin >> a >> b >> c;
    std::cout << "a = " << a << ", b = " << b << ", c = " << c << '\n';
    return 0;
}

why std::cin doesn't give error on "char"

3 Answers3