Need RegQuery help

hey, i'm trying to check if a registry key exists and i open the key with this code:

Code:

/* variables */
TCHAR szBuf[20] = "Software\\ShibbyInc", value[9] = "Password";
LPDWORD type;
LONG regresult;
HKEY hkey;

if (RegOpenKeyEx(HKEY_CURRENT_USER, szBuf, 0, KEY_READ, &hkey)) 
{   return FALSE;   }

and then i need to query it (i believe) because i need to check if a key exists which the program creates depending on the user, and then if the key is there i need the value stored. so i've tried:

Code:

regresult = RegQueryValueEx(hkey, value, NULL, type, NULL, NULL);
if (regresult == ERROR_SUCCESS) MessageBox(hwnd, "it exists.", "ok", MB_OK);

and

if (RegQueryValueEx(hkey, value, NULL, type, NULL, NULL))
MessageBox(hwnd, "it exists.", "ok", MB_OK);

but with either query, i get the Windows message saying i violated memory what am i doing wrong?
thanks

When a function takes a pointer, it expects a value that is either NULL (when allowed by the documentation) or a value that points somewhere valid. It never expects a random value.

Code:

// type is not initialized and therefore has a "random" value.
LPDWORD type; 

// Whoops, crash when function tries to write to random memory address
regresult = RegQueryValueEx(hkey, value, NULL, type, NULL, NULL);

Either of these are valid:

Code:

regresult = RegQueryValueEx(hkey, value, NULL, NULL, NULL, NULL);

or:

Code:

DWORD type;
// Pass a valid pointer to a DWORD variable...
regresult = RegQueryValueEx(hkey, value, NULL, &type, NULL, NULL);

ahh, things are much more clear now thank you.

Code:

LONG RegQueryValueEx(
  HKEY hKey,
  LPCTSTR lpValueName,
  LPDWORD lpReserved,
  LPDWORD lpType,
  LPBYTE lpData,
  LPDWORD lpcbData
);

what datatypes are useable / required for the second to last variable (LPBYTE lpData) ? should i use a typecase operator with like, a TCHAR or something?
thanks

It depends on the type of the registry value that you are requesting. If it's a DWORD value, lpData should be a pointer to a DWORD. If it's a string, lpData should specify a TCHAR array. If it's binary, lpData should specify a BYTE array. You will need to use a cast for this argument. Here are a couple of functions that demonstrate.

Code:

// =====================================================================================
HRESULT RegGetString(HKEY hKey, LPCTSTR szValueName, LPTSTR * lpszResult) {

	// Given a HKEY and value name returns a string from the registry.
	// Upon successful return the string should be freed using free()
	// eg. RegGetString(hKey, TEXT("my value"), &szString);

	DWORD dwType=0, dwDataSize=0, dwBufSize=0;
	LONG lResult;

	// Incase we fail set the return string to null...
	if (lpszResult != NULL) *lpszResult = NULL;

	// Check input parameters...
	if (hKey == NULL || lpszResult == NULL) return E_INVALIDARG;

	// Get the length of the string in bytes (placed in dwDataSize)...
	lResult = RegQueryValueEx(hKey, szValueName, 0, &dwType, NULL, &dwDataSize );

	// Check result and make sure the registry value is a string(REG_SZ)...
	if (lResult != ERROR_SUCCESS) return HRESULT_FROM_WIN32(lResult);
	else if (dwType != REG_SZ)    return DISP_E_TYPEMISMATCH;

	// Allocate memory for string - We add space for a null terminating character...
	dwBufSize = dwDataSize + (1 * sizeof(TCHAR));
	*lpszResult = malloc(dwBufSize);

	if (*lpszResult == NULL) return E_OUTOFMEMORY;

	// Now get the actual string from the registry...
	lResult = RegQueryValueEx(hKey, szValueName, 0, &dwType, (LPBYTE) *lpszResult, &dwDataSize );

	// Check result and type again.
	// If we fail here we must free the memory we allocated...
	if (lResult != ERROR_SUCCESS) { free(*lpszResult); return HRESULT_FROM_WIN32(lResult); }
	else if (dwType != REG_SZ)    { free(*lpszResult); return DISP_E_TYPEMISMATCH; }

	// We are not guaranteed a null terminated string from RegQueryValueEx.
	// Explicitly null terminate the returned string...
	(*lpszResult)[(dwBufSize / sizeof(TCHAR)) - 1] = TEXT('\0');

	return NOERROR;
}


// =====================================================================================
HRESULT RegGetDWord(HKEY hKey, LPCTSTR szValueName, DWORD * lpdwResult) {

	// Given a value name and an hKey returns a DWORD from the registry.
	// eg. RegGetDWord(hKey, TEXT("my dword"), &dwMyValue);

	LONG lResult;
	DWORD dwDataSize = sizeof(DWORD);
	DWORD dwType = 0;

	// Check input parameters...
	if (hKey == NULL || lpdwResult == NULL) return E_INVALIDARG;

	// Get dword value from the registry...
	lResult = RegQueryValueEx(hKey, szValueName, 0, &dwType, (LPBYTE) lpdwResult, &dwDataSize );

	// Check result and make sure the registry value is a DWORD(REG_DWORD)...
	if (lResult != ERROR_SUCCESS) return HRESULT_FROM_WIN32(lResult);
	else if (dwType != REG_DWORD) return DISP_E_TYPEMISMATCH;

	return NOERROR;
}