Clear the screen

[Duthomhas]

This short article describes the method of clearing the console display of all text and positioning the text cursor in the home location (the upper-left corner).

Before becoming too comfortable doing this kind of thing blithely, make sure you read and understand Types and purposes of console applications.

- - - - - - - - - - - - - - - - The Simple Answer - - - - - - - - - - - - - - - -

While simple, it really is a Bad Thing. See Why system() is evil for more.

#ifdef __cplusplus__
  #include <cstdlib>
#else
  #include <stdlib.h>
#endif

if (system("CLS")) system("clear");

- - - - - - - - - - - - - - - - The Standard Way - - - - - - - - - - - - - - - -

Pathetic, but passing, and usually correct.

#ifdef __cplusplus__

  #include <iostream>
  #include <string>

  void ClearScreen()
    {
    cout << string( 100, '\n' );
    }

#else

  #include <stdio.h>

  void ClearScreen()
    {
    int n;
    for (n = 0; n < 10; n++)
      printf( "\n\n\n\n\n\n\n\n\n\n" );
    }

#endif 

This works, of course, just by putting a hundred newlines to the display. Over a poorly-buffered network connection, this might be s l o w. Alas.

- - - - - - - - - - - - - - - - Using NCurses - - - - - - - - - - - - - - - -

The Curses library is designed for working with the console. Advantages: it is cross-platform. Disadvantages: it doesn't interact well with the standard streams. In other words, you shouldn't mix printf(), etc or cout, etc with curses. Use one or the other, not both.

#include <curses.h>

int main()
  {
  char users_name[ 100 ];

  initscr();
  (void)echo();

  addstr( "What is your name> " );
  refresh();
  getnstr( users_name, sizeof( users_name ) - 1 );

  clear();

  printw( "Greetings and salutations %s!\n", users_name );
  refresh();

  printw( "\n\n\nPress ENTER to quit." );
  refresh();
  getnstr( users_name, sizeof( users_name ) - 1 );

  endwin();
  return 0;
  }  

Again, if all you want to do is clear the screen on occasion then using Curses is complete overkill.

- - - - - - - - - - - - - - - - Using <conio.h> - - - - - - - - - - - - - - - -

This library is severely deprecated, but it is so popular that some form of it exists on most 80x86 hardware compilers --almost always on Windows compilers, and there exist Linux versions too. However, given the choice, use NCurses instead...

The caveat is that it is non-standard, meaning that the actual functions it provides vary a lot and they don't always behave just right. Hence, for anything other than Windows programs it is also a sub-optimal solution. See Using <conio.h> for more.

If undaunted, then here's the code:

#include <conio.h>
#include <stdio.h>
#include <string.h>

int main()
  {
  char users_name[ 100 ];

  printf( "What is your name> " );
  fgets( users_name, sizeof( users_name ), stdin );
  *strchr( users_name, '\n' ) = '\0';

  clrscr();

  printf( "Greetings and salutations %s!\n", users_name );

  printf( "\n\n\nPress ENTER to quit." );
  fgets( users_name, sizeof( users_name ), stdin );

  return 0;
  }

Now, the enterprising among you may have tried to compile this. If it worked for you, you're lucky. If not, then you have learned firsthand the shortcomings of the <conio.h> library. Alas.

[Duthomhas]

- - - - - - - - - - - - - - - - OS-specific ways - - - - - - - - - - - - - - - -

So, on to the part for those of us who have the hack nature.

Windows

#include <windows.h>

void ClearScreen()
  {
  HANDLE                     hStdOut;
  CONSOLE_SCREEN_BUFFER_INFO csbi;
  DWORD                      count;
  DWORD                      cellCount;
  COORD                      homeCoords = { 0, 0 };

  hStdOut = GetStdHandle( STD_OUTPUT_HANDLE );
  if (hStdOut == INVALID_HANDLE_VALUE) return;

  /* Get the number of cells in the current buffer */
  if (!GetConsoleScreenBufferInfo( hStdOut, &csbi )) return;
  cellCount = csbi.dwSize.X *csbi.dwSize.Y;

  /* Fill the entire buffer with spaces */
  if (!FillConsoleOutputCharacter(
    hStdOut,
    (TCHAR) ' ',
    cellCount,
    homeCoords,
    &count
    )) return;

  /* Fill the entire buffer with the current colors and attributes */
  if (!FillConsoleOutputAttribute(
    hStdOut,
    csbi.wAttributes,
    cellCount,
    homeCoords,
    &count
    )) return;

  /* Move the cursor home */
  SetConsoleCursorPosition( hStdOut, homeCoords );
  }

POSIX (Unix, Linux, Mac OSX, etc)

#include <unistd.h>
#include <term.h>

void ClearScreen()
  {
  if (!cur_term)
    {
    int result;
    setupterm( NULL, STDOUT_FILENO, &result );
    if (result <= 0) return;
    }

  putp( tigetstr( "clear" ) );
  }

You'll have to link to the proper library (one of -lcurses, -lterminfo, etc) to compile that last one.

Until next time!

[mmlb]

hello, We use clear screen for clear console woindow..
We use clrscr(); for clear screen.
But 1stly we add its header file, which is conio.h ..
like
#include<iostream.h>
#include<conio.h>

void main()

{
clrscr();
cout<<"Waw screen is clear";
getch();
}

If yoe are not include conio.h then its creat an error..

i make 1 very wonderful code for all new comers n youngers...

// For All new Comers Student....

#include<iostream.h>
#include<conio.h> // We use conio to get output on console secreen..
// Its also use for Clear screen
#include<stdlib.h> // use for exit();
void main()
{
clrscr(); //---> Must be put on start:P..

int op;
int n1,n2;
while(1) // use for infinite n 5 for exit.
{
clrscr(); // --->> This clr scr use for clear screen on every keys u enter..
cout<<"Enter 1 for addition.. "<<endl;
cout<<"Enter 2 for Subtraction.. "<<endl;
cout<<"Enter 3 for multiplication.. "<<endl;
cout<<"Enter 4 for division.. "<<endl;
cout<<"Enter 5 for Exit.. "<<endl;
op=getche(); // u get chracter instead of integer so loop not b infinite
cout<<endl;
switch(op) // ye use switch or if else conditional staement..
{
case '1':
cout<<"Enter n1: "; cin>>n1;
cout<<"Enter n2: "; cin>>n2;
cout<<"Additin answer is: "<<n1+n2<<endl;
getch();
break;
case '2':
cout<<"Enter n1: "; cin>>n1;
cout<<"Enter n2: "; cin>>n2;
if(n1>n2)
{
cout<<"Subtraction answer is: "<<n1-n2<<endl;
getch();
}
else
{
cout<<"Subtraction answer is: "<<n2-n1<<endl;
getch();
}
break;
case '3':
cout<<"Enter n1: "; cin>>n1;
cout<<"Enter n2: "; cin>>n2;
cout<<"Multiplication answer is: "<<n1*n2;
getch();
break;
case '4':
cout<<"Enter n1: "; cin>>n1;
cout<<"Enter n2: "; cin>>n2;
if(n1>n2)
{
cout<<"Division answer is: "<<n1/n2<<endl;
getch();
}
else
{
cout<<"Divison answer is: "<<n2/n1<<endl;
getch();
}
break;
case '5':
cout<<"Program is Exit..";
getch(); //use getch or delay..
exit(1); // is just read 1 above state ment
// if u put 2 instead of 1, then its print above 2 statement..
break;
}
}
getch();
}



For more contact: [e-mail]

[z05DSL3A]

mmlb, conio.h is not a good way to go, it is non standard and varies significantly from compiler to compiler.
The first example code that you posted:

#include<iostream.h>
#include<conio.h>

void main()

{
clrscr();
cout<<"Waw screen is clear";
getch();
}

will not even compile with MS C++.

[Duthomhas]

Heh heh heh... I think it amazing the amount of spam threads like this attract.

[mmlb]

ahan grey wolf:P.. Well its example of Borland C..
We no need to include conio.h in MS C++..

[Duthomhas]

Quit dinking with nonstandard stuff.

If you must clear the screen, then why not just use the proper Windows or POSIX functions I gave you?
http://www.cplusplus.com/forum/articles/10515/page1.html#msg49080

The whole point of this thread is how to do things the Right Way; it is not "Every possible variation of how to do things the Wrong Way".

[osmartechy05]

Hello, everyone! I'm a beginner like some around here and this is in fact my first post. I have read that some Visual C++ 2005 or 2008 users couldn't use: system ("cls") to clear the screen besides I've heard it's a bad habit. I have Visual 2005 and what I do is writing this piece of code:

System::Console::Clear();

I use it cus doing so I avoid putting some extra code or including header files and such. But as I said before I'm a complete beginner and I want to know if it's also a bad practice??

[Disch]

That thar must be .net

Not really part of standard C++. It's fine if you're developing .net programs though.

[Hammurabi]

It should be pointed out that "The Standard Way" does not position the cursor in the upper-left corner, so it doesn't quite do the same job as the others.

[rcorreia]

Hi, in this my first post ... my question is : Why not use the ANSI Terminal escapes controls ? just like "033]" and follow ? Look this snippet code :

printf("\033[2J"); // from <stdio.h>

thanks.

[Duthomhas]

Because not all terminals accept ANSI terminal escape codes. (DOS, remember, requires you to load ANSI.SYS just to use a small subset of the ANSI/VT100+ codes.)

On Windows, clear it the Windows way.

On POSIX systems (Unix/Linux/etc), use the terminfo database like I showed you to output the correct terminal control sequence. (Which might very well be "\033[2J" if your program is running on a VT100+ compatible terminal/emulator, like xterm.)

The difference is that when you use the function I gave you, your programs will work on any terminal listed in the terminfo database, but if you just dump terminal codes you 1) bind yourself to a specific subset of terminal/emulators, and 2) introduce nasty surprises when fancy control sequences aren't emitted like you wrote them.
http://www.cplusplus.com/forum/articles/10515/page1.html#msg49080

Hope this helps.

[hypercube1]

This is not quite on topic and im sure that if i looked i could find a thread that covers this but why do you people (mmlb) insist on using void main(). It makes no sense with expected return values.

[firedraco]

It's because they fail and compilers sometimes support so they can keep supporting "legacy" code.

[hypercube1]

Well that seems like the lazy way to avoid errors with returns but i'll have to look into 'legacy' code. i assume that it is old code using void main(), but...

[firedraco]

Actually the standard says that you can't EVER use void main() but some old compilers let you and now everyone "has" to support that...(they shouldn't IMO).

[helios]

The standard allows main() not to return anything even if it does have int as its return type, so considering there can be only one main(), I don't think it makes much sense for compilers to allow void main().

[hypercube1]

@ firedraco: that's what i thought

[Kiana]

@helios: I always wondered, when a program's entry point returns something, where does it return it to?

[helios]

That's system-dependent.
All OSs I know of pass the return value to the shell so scripts can use it to determine the result of the program.