The keyboad hook dll can't work well - winapi

Question

The code of keyhook.cpp in dll:
// KeyHook.cpp : 定义 DLL 应用程序的导出函数。
//
#include "stdafx.h"
#include "stdio.h"
#include "Windows.h"
#pragma comment(linker, "/SECTION:.SHARED,RWS")
#pragma data_seg(".SHARED")
#define DEF_PROCESS_NAME "notepad.exe"
HINSTANCE g_hInstance = NULL;
HHOOK g_hHook = NULL;
HWND g_hWnd = NULL;
#pragma data_seg()
BOOL APIENTRY DllMain(HINSTANCE hModule,DWORD ul_reason_for_call,LPVOID lpReserved)
{
printf("main function in dll\n");
switch (ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
g_hInstance = hModule;
printf("max=%d\n", MAX_PATH);
break;
case DLL_PROCESS_DETACH:
break;
}
return TRUE;
}
LRESULT CALLBACK KeyboardProc(int nCode, WPARAM wParam, LPARAM lParam)
{
//OutputDebugString("what the hell\n");
char szPath[MAX_PATH] = { 0, };
char *p = NULL;
//printf("the callback function");
int shift = nCode;
if (shift = 0)
{
if (!(lParam & 0x80000000))
{
GetModuleFileNameA(NULL, szPath, MAX_PATH);
p = strrchr(szPath, '\\');
//printf("szPath=%s\n", szPath);
OutputDebugString("what the hell\n");
if (!_stricmp(p + 1, DEF_PROCESS_NAME))
return 1;
}
}
return CallNextHookEx(g_hHook, nCode, wParam, lParam);
}
#ifdef __cplusplus
extern "C" {
#endif // DEBUG
__declspec(dllexport) void HookStart()
{
printf("hookstart function\n");
g_hHook = SetWindowsHookEx(WH_KEYBOARD, KeyboardProc, g_hInstance, 0);
if (g_hHook == NULL)
printf("failed to install the keyboard hook");
else
{
printf("Succeed in installing the keyboard hook");
}
}
__declspec(dllexport) void HookStop()
{
if (g_hHook)
{
UnhookWindowsHookEx(g_hHook);
g_hHook = NULL;
}
printf("hookstop function\n");
}
#ifdef __cplusplus
}
#endif // DEBUG
The calling application code:
// hkeybi.cpp : 定义控制台应用程序的入口点。
#include "stdafx.h"
#include<stdio.h>
#include<conio.h>
#include<Windows.h>
#define DEF_DLL_NAME "KeyHook.dll"
#define DEF_HOOKSTART "HookStart"
#define DEF_HOOKSTOP "HookStop"
typedef void(*PFN_HOOKSTART)();
typedef void(*PFN_HOOKSTOP)();
int main()
{
int ch = -1;
HMODULE hDll = NULL;
PFN_HOOKSTART HookStart = NULL;
PFN_HOOKSTOP HookStop = NULL;
hDll = LoadLibraryA(DEF_DLL_NAME);
HookStart = (PFN_HOOKSTART)GetProcAddress(hDll, DEF_HOOKSTART);
HookStop = (PFN_HOOKSTOP)GetProcAddress(hDll, DEF_HOOKSTOP);
if ((HookStart != NULL) && (HookStop != NULL))
printf("hello start\n");
HookStart();
printf("press q to exit!\n");
while (_getch() != 'q');
HookStop();
FreeLibrary(hDll);
return 0;
}
When I run the app,after I input several words,it will go down. I spent long time in solving the problem.

Answer 1

There are several problems in your KeyboardProc function. The first one being that your shift variable is assigned instead of tested:
if (shift = 0)
The variable is assigned 0, the condition is therefore always false. Effectively, the only code executed after the test is the return CallNextHookEx(...). If the condition would be true, you may run into problems because the GetModuleFileNameA result is not tested. In case of an error, the following strrchr will likely fail and the p pointer will be NULL. This will result in a crash at the _stricmp. And why do you specifically use the ANSI version of GetModuleFileName, are you sure you're not using Unicode? Finally, returning the hook proc without calling CallNextHookEx is a bad idea. Here's what the documentation says:
If code is greater than or equal to zero, and the hook procedure did
not process the message, it is highly recommended that you call
CallNextHookEx and return the value it returns