Windows SDK User Interface: How can I emulate keyboard events in an application?

[golanshahar]

Q: How can I emulate keyboard events in an application?

A:

• There are two API functions that you can use:
  
  
  • 'keybd_event()'
  • 'SendInput()'.
  
  
  Before emulating a keystroke we must make sure that:
  
  
  • The window we want to send the keystroke must be in focus and active.
  • That we have the virtual key code for the key we want to generate.
  
  
  The keys 'A-Z' and the keys '0-9' have a virtual key code that is the same as their ASCII code. For example, in order to generate the letter A we need to use the 'A' (or 65) as the virtual key code.
  
  Look here for a complete list of virtual key codes.
  
  
  
  
• Which of the two API functions should I use?
  
  The 'keybd_event()' function has been superseded by 'SendInput()' on Window NT/2000/XP. Thus, on these operating systems you should use 'SendInput()' (unless you need to provide backward compatibility with Windows 98 etc.). This FAQ is based on 'SendInput()'.
  
  
  
  
• Can I see some example on how to use 'SendInput()'?
  
  
  

  void GenerateKey ( int vk , BOOL bExtended)
  {
    KEYBDINPUT  kb={0};
    INPUT    Input={0};
    // generate down 
    if ( bExtended )
      kb.dwFlags  = KEYEVENTF_EXTENDEDKEY;
    kb.wVk  = vk;  
    Input.type  = INPUT_KEYBOARD;
  
    Input.ki  = kb;
    ::SendInput(1,&Input,sizeof(Input));
  
    // generate up 
    ::ZeroMemory(&kb,sizeof(KEYBDINPUT));
    ::ZeroMemory(&Input,sizeof(INPUT));
    kb.dwFlags  =  KEYEVENTF_KEYUP;
    if ( bExtended )
      kb.dwFlags  |= KEYEVENTF_EXTENDEDKEY;
  
    kb.wVk    =  vk;
    Input.type  =  INPUT_KEYBOARD;
    Input.ki  =  kb;
    ::SendInput(1,&Input,sizeof(Input));
  }

  
  
• How to use the function?
  
  Suppose we want to generate 'a' key and then 'A' key:
  
  
  

  GenerateKey ('A', FALSE);
  GenerateKey (VK_CAPITAL, TRUE);
  GenerateKey ('A', FALSE);

  
  The output will be 'aA' (in case the 'CapsLock' initial state is on, the output will be 'Aa').
  
  
  NOTE:
  
  
  • In case 'CapsLock' is pressed the letter that will be generated will be uppercase ('A')
  • The generated letter also depends on the input locale of thread that will receive the key.

Thanks to cilu for helping writing this FAQ.