Print to console without flooding in C++

Question

My apologies for an inaccurate title, but I'm not sure what this is called exactly.

How would one print to the console a single, updating line?

For example, if I wanted to print a percent completion status every cycle but not flood the console with steams of text, how would I accomplish this? (What is this called? -- for future Googling)

Thank you!

Answer 1

There is no portable way to clean the screen though there is a simple way to return to the beginning of the line using \r then overwriting what we wrote before. I am using Sleep from Windows API:

#include <iostream>
#include <windows.h>
using namespace std;

int main()
{
 for(int i = 1; i <= 10; i++)
 {
  std::cout << i*10 << '%';
  std::cout.flush(); // see wintermute's comment
  Sleep(1000);
  std::cout << '\r';
 }
}

Answer 2

The basic solution is to:

loop:
    backspace (over written text)
    write (without newline)
    flush
    wait and get updates

Alternatively, you could try a solution using the curses library - though I'm not sure whether this is quite what you're after. Curses provides your basic ascii graphics for text based GUIs (sometimes called a TUI).

Answer 3

Curses is only way to do this portably.

A quick google led me too:

http://code.google.com/p/tinycurses/wiki/basic1

Answer 4

How fast are your cycles? Are they in the millisecond, or seconds. If your cycles are short, you may only want to update the screen after a second as elpased.

For example

   include <time.h>  /* if memory serves me correctly */
   int currentTime = time(0);
   for ( int i = 0; i < 100; i++)
   {
     /* do work here  and save the percentage completed */
     lastTime = time(0);
     if ((lastTime-currentTime) >= 1 ) 
     {
       /* output percentage completed (using AraK information) */
       currentTime = lastTime;
     }
   }

This will only update the screen every second and save the time writing to the screen as it consumes time to redraw the screen (which you can use for processing). In addition, if your updates go so fast, this lets the user see the percentage if your cycles are quite short, as you could be redrawing the screen all of the time.

Note: Updated based on comments.

Answer 5

This depends on the platform you are using. I'm not sure how you do this on Linux, but on Windows you can either use WriteConsole or SetConsoleCursorPosition to do this.

I don't believe a completely portable way to do this exists other than outputting a ton of backspaces as already mentioned. The backspace method can cause a lot of flicker which may be unacceptable in your application ... the Win32 functions do not cause flicker. Not sure about the curses library.