CODEWITHSUNDEEP
c++console-applicationcarriage-return
John Sall
John Sall

Reputation: 1151

How to get rid of left-over characters when using \r in C++?

Assume I have the following code which is an infinit counter :

#include <iostream>

int main() {

    short int counter = 0;

    while(true) 
        cout << "This is a counter: " << counter++ << " and I'll keep counting!\r";

    return 0;
}

When you run the code with the carriage return, it will overwrite the existing text, but at the end there will be more than one '!'. Is there away to fix this without calling clear screen to avoid flickering?

Upvotes: 1

Views: 172

Answers (2)

Asteroids With Wings
Asteroids With Wings

Reputation: 17454

You could first write a line of just spaces to the "maximum" expected length, itself with a \r at the end.

Alternatively, on each iteration count how many spaces you might need to pad the end of your new line to reach that maximum.

Upvotes: 1

David C. Rankin
David C. Rankin

Reputation: 84559

Continuing from the comments above, if you are outputting to a VT compatible terminal (most are), you can use ANSI Escape sequences to control clearing to end-of-line (and various other cursor movements and visibility).

A short example working with lines terminated with a carriage-return, you can use \033[K to clear to end of line. (the formal number preceding 'K' is "0K" but can be omitted due to it being the default) The other line clearing options are "1K" clear to beginning of line, and "2K" clear entire line. You can also hide and restore the cursor with similar escapes.

In your case you can handle the additional characters from previous longer lines as:

#include <iostream>
#include <unistd.h>

int main (void) {
    
    const char *lines[] = { "You do not ever want\r", 
                            "your favorite dog\r", 
                            "to have\r",
                            "fleas!\r" };
    int n = sizeof lines / sizeof *lines;
    
    std::cout << "\033[?25l";                   /* hide cursor */
    
    for (int i = 0; i < n; i++) {
        std::cout << "\033[0K" << lines[i];     /* clear to end, output line */
        std::fflush (stdout);
        sleep (2);
    }
    
    std::cout << "\033[?25h\n";                 /* restore cursor */
}

Compile normally and run in your terminal. If it is VT compatible it will process the escapes so you see each line printed without any of the additional characters from the preceding line interfering with the output.

Upvotes: 1

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