c++ - Global keyboard hook with WH_KEYBOARD_LL and keybd_event (windows) -

i trying write simple global keyboard hook program redirect keys. example, when program executed, press 'a' on keyboard, program can disable , simulate 'b' click. not need graphic ui, console enough (keep running)

my plan use global hook catch key input, , use keybd_event simulate keyboard. have problems.

the first problem program can correctly block 'a' if hit 'a' on keyboard once, printf in callback function executed twice, keybd_event. if open txt file, click 'a' once, there 2 'b's input. why that?

the second question why hook using of wh_keyboard_ll can work on other process without dll? thought had use dll make global hook until wrote example...

#include "stdafx.h" #include <windows.h> #define _win32_winnt 0x050  lresult callback lowlevelkeyboardproc(int ncode, wparam wparam, lparam lparam) {     bool featkeystroke = false;      if (ncode == hc_action)     {         switch (wparam)         {         case wm_keydown:         case wm_syskeydown:         case wm_keyup:         case wm_syskeyup:             pkbdllhookstruct p = (pkbdllhookstruct)lparam;             if (featkeystroke = (p->vkcode == 0x41)) {     //redirect b             printf("hello a\n");             keybd_event('b', 0, 0, 0);             keybd_event('b', 0, keyeventf_keyup, 0);             break;             }             break;         }     }     return(featkeystroke ? 1 : callnexthookex(null, ncode, wparam, lparam)); }  int main() {     // install low-level keyboard & mouse hooks     hhook hhklowlevelkybd = setwindowshookex(wh_keyboard_ll, lowlevelkeyboardproc, 0, 0);      // keep app running until we're told stop     msg msg;     while (!getmessage(&msg, null, null, null)) {    //this while loop keeps hook         translatemessage(&msg);         dispatchmessage(&msg);     }      unhookwindowshookex(hhklowlevelkybd);      return(0); } 

many thanks!

first 1 easy. 1 key down , key up. :)

as why can work without dll - that's because global hook. unlike thread-specific ones executed in own process, not in process keyboard event happened. done via message sending thread has installed hook - that's precisely why need message loop here. without hook can't ran there no 1 listen incoming messages.

the dll required thread-specific hooks because they're called in context of process. work, dll should injected process. not case here.