Thread: cin + copy paste

Hi,

When I copy paste a text in the command prompt for one of the "cin" the text will gets in the other too and loops 3 or 4 times.
Its a text without space so it shouldn't get fragmented.
I tried to use cin.ignore(); and fflush(stdin); but it won't change a thing.

What's happening here?

Edit: apparently its the new line that causes it but wouldn't cin.ignore(); and fflush(stdin); should empty what's in "cin" ?

Code:

#include <string>
#include <iostream>
using namespace std;

int main()
{
    string response;
    char buf[1255];
    while(1)
    {
        cin >> response;
        cout << "string: "<<response << endl;
        cin >> buf;
        cout << "buf: "<< buf << endl;
    }

    return 0;
}

fflush(stdin) has undefined behaviour, so there's nothing it should do.

You haven't shown the input you are providing and the output you are getting. But yes, cin will stop at the newline.

Thanks, so what should we use to flush cin?
For that the second time it is called there would be nothing in it.

input:
aaa
bbb
ccc
ddd

output:
aaa
string aaa
bbb
buf bbb
ccc
string ccc
ddd

Ducky, you should know that you should never do this kind of thing:

char buf[1255];
cin >> buf;

Reading into char arrays like this can cause a buffer overflow. So use a std::string. Always (that is, if you intend to read a string from the input).
Also be aware that cin >> stops at whitespace, so spaces in the text will make it stop.
If you want to fetch a single line, then use std::getline. Again, this will not read the entire input. It will stop at newlines.
Reading everything pasted (including newlines) is very difficult with standard C++ (because there is no good way to know when there is no more characters in the input buffer and any reads when there is no more input will block). You may have to use workarounds or some native API or library to do it.

Thank you Elysia, that's very clearly explained.

Is that on purpose that there is no way to flush it between calls or is it a design flaw?

You can flush the input buffer. But if you do that, then you might risk missing stuff.
Anyway, to flush the input buffer, normally one would do:

std::cin.ignore(std::numerical_limits<std::streams ize>::max());