47. FAQ o Win API

Q> Как поменять default принтер?

A> 

int CALLBACK WinMain( HINSTANCE hInst, HINSTANCE hPrevInst,
                LPSTR lpCmdLine, int nShowCmd )
{
  /* Get the port & device settings for the specified printer */
 char szDeviceString[260];

  /* First (and only) parameter is the printer name */
        lstrcpy( szDeviceString, __argv[1] );
        const int Pos = lstrlen( szDeviceString );

  /* Append a ',' */
        szDeviceString[ Pos ] = ',';

        GetProfileString( "Devices", __argv[1], "",
                        &szDeviceString[Pos+1],
                        sizeof( szDeviceString ) - (Pos+1) );

  /* Have we got the printer? */
        if ( szDeviceString[Pos+1] != '\0' )
        {
          /* Set the default printer */
                WriteProfileString( "windows", "device", szDeviceString );

                SendMessageTimeout( HWND_BROADCAST, WM_SETTINGCHANGE, 0L,
                        (LPARAM)(LPCTSTR)"windows", SMTO_NORMAL,
                        1000, NULL );
        }
        else
        {
                MessageBox( NULL, "Printer not found",
                        "Set Default Printer Utility",
                        MB_OK | MB_ICONERROR );
        }

        return 0;
}

References and samples:

Knowledge Base Article Q135387: "How to Get and Set the Default Printer in 
Windows" 

Knowledge Base Article Q140560 "How to Set the Default Printer Programmatically
in Windows 95"