How does a string gets displayed 'after' pressing ENTER even though std::cout was used for/after each character in the given code?

Question

It's a program which reads the input character by character, and prints it in the same way. The conceptual doubt I'm having here is that how is the complete string being displayed only on pressing ENTER key, even though std::cout was used on every iteration of taking each character input?

int main()
{
 char c;
 while(1)
 {
     c = cin.get();
     if(cin.eof())
         break;
     else cout << c;
 }
 return 0;
}

Don't tag C++ questions with the C tag; the two languages are quite different. — Jonathan Leffler, May 24 '21 at 14:07
you are presumably using a line buffered terminal that doesn't send the input data to your application until you press enter — Alan Birtles, May 24 '21 at 14:08
std::cout is a stream, and it might not flush until it reads a newline. You can force flush using std::flush — Bas in het Veld, May 24 '21 at 14:08
The terminal driver doesn't let any characters go to the program until you hit return. Read about [Canonical vs non-canonical terminal input](https://stackoverflow.com/q/358342/15168). — Jonathan Leffler, May 24 '21 at 14:09
related: https://stackoverflow.com/questions/22026751/c-force-stdcout-flush-print-to-screen — Bas in het Veld, May 24 '21 at 14:09

score 0 · Answer 1 · answered May 24 '21 at 16:00

Lets examine your code:

#include <iostream>
using namespace std;

int main()
{
    char c;
    while (1)
    {
        c = cin.get();
        if (cin.eof())
            break;
        else cout << c;
    }
    return 0;
}

In our first line, we make a char. Then we enter a while loop. cin.get() waits until the user hits enter, then flushes and puts the input into a buffer. cin.get() then returns the first char in the buffer, and removes the char it returned. if (cin.eof()) does not execute, because we did not put a EOF yet. On the next loops, cin.get() grabs the remaining chars in the buffer, and when the buffer is empty, waits for the user to enter more input and hit enter.

std::cin is buffered, so you will not get input instantly.

Also, read on Why is iostream::eof inside a loop condition (i.e. `while (!stream.eof())`) considered wrong?.

How does a string gets displayed 'after' pressing ENTER even though std::cout was used for/after each character in the given code?

1 Answers1