CODEWITHSUNDEEP
cwindowsconsole
Agi Hammerthief
Agi Hammerthief

Reputation: 2134

How do I clear a win32 cmd console window without using system() in C?

Having looked around for the best way to perform the (supposedly) simple task of clearing a cmd.exe console window and finding out that simply using system('cls'); is wrong (in the line of "For every complex problem there is an answer that is clear, simple, and wrong") and finding that simply copying and pasting the win32 code into a function results in compilation errors, I then found the following function, but have no idea what I have to do to call it with a variable it can work with without spewing error messages:

#include <windows.h>
#include <stdlib.h>
#include <stdio.h>

/* Standard error macro for reporting API errors */ 
#define PERR(bSuccess, api){ if(!(bSuccess)) printf("%s:Error %d from %s \
  on line %d\n", __FILE__, GetLastError(), api, __LINE__); }

HWND GetConsoleHwnd(void) {
  #define MY_BUFSIZE 1024  // Buffer size for console window titles.
  HWND hwndFound;  // This is what is returned to the caller.
  char pszNewWindowTitle[MY_BUFSIZE]; // Contains fabricated WindowTitle.
  char pszOldWindowTitle[MY_BUFSIZE]; // Contains original WindowTitle.

  // Fetch current window title.
  GetConsoleTitle(pszOldWindowTitle, MY_BUFSIZE);
  // Format a "unique" NewWindowTitle.
  wsprintf(pszNewWindowTitle,"%d/%d", GetTickCount(), GetCurrentProcessId());
  // Change current window title.
  SetConsoleTitle(pszNewWindowTitle);
  // Ensure window title has been updated.
  Sleep(40);

  // Look for NewWindowTitle.
  hwndFound=FindWindow(NULL, pszNewWindowTitle);
  // Restore original window title.
  SetConsoleTitle(pszOldWindowTitle);

  return(hwndFound);
}

void cls( HANDLE hConsole ) {
  COORD coordScreen = { 0, 0 };  /* here's where we'll home the cursor */ 
  BOOL bSuccess;
  DWORD cCharsWritten;
  CONSOLE_SCREEN_BUFFER_INFO csbi;  /* to get buffer info */ 
  DWORD dwConSize;  /* number of character cells in the current buffer */ 

  /* get the number of character cells in the current buffer */ 
  bSuccess = GetConsoleScreenBufferInfo( hConsole, &csbi );
  PERR( bSuccess, "GetConsoleScreenBufferInfo" );
  dwConSize = csbi.dwSize.X * csbi.dwSize.Y;

  /* fill the entire screen with blanks */ 
  bSuccess = FillConsoleOutputCharacter( hConsole, (TCHAR) ' ',
    dwConSize, coordScreen, &cCharsWritten );
  PERR( bSuccess, "FillConsoleOutputCharacter" );

  /* get the current text attribute */ 
  bSuccess = GetConsoleScreenBufferInfo( hConsole, &csbi );
  PERR( bSuccess, "ConsoleScreenBufferInfo" );

  /* now set the buffer's attributes accordingly */ 
  bSuccess = FillConsoleOutputAttribute( hConsole, csbi.wAttributes,
    dwConSize, coordScreen, &cCharsWritten );
  PERR( bSuccess, "FillConsoleOutputAttribute" );

  /* put the cursor at (0, 0) */ 
  bSuccess = SetConsoleCursorPosition( hConsole, coordScreen );
  PERR( bSuccess, "SetConsoleCursorPosition" );

  return;
}

int main (void) {
  // why does this fail?
  HWND cons = GetConsoleHwnd();
  cls(cons);

  return 0;
}

My question is this: How do I set up a console handle to pass to the `cls` function?

Edit: Please note that I do not wish to simply call/invoke the cls or clear command(s) via a call to system as advised in the majority of answers to this question.

Upvotes: 3

Views: 3907

Answers (1)

Anton Kovalenko
Anton Kovalenko

Reputation: 21507

Get the console handle using GetStdHandle(STD_OUTPUT_HANDLE) if the standard output was not redirected. If it could be redirected but you want to clear the real console nevertheless, open the CONOUT$ pseudo-file using CreateFile function.

Upvotes: 7

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