How to convert LPWSTR* (or WCHAR*) to LPWSTR - c++

Question

I'm having a difficulty in converting a value to LPWSTR. I'm getting a registry value, and trying to return the result as LPWSTR. It appears the registry call using RegQueryValueExW works with a variety of types going in to store the result, but I can't cast any of them back to LPWSTR.
LPWSTR value;
HKEY hKey;
long result = RegOpenKeyExW(HKEY_LOCAL_MACHINE, L"RegEntry1", 0, ACCESS|KEY_WOW64_32KEY, &hKey);
if (result == ERROR_SUCCESS)
{
//WCHAR buffer[512];
//TCHAR buffer[512];
LPWSTR buffer[512];
DWORD bufferSize = sizeof(buffer);
ULONG queryVal = 0;
queryVal = RegQueryValueExW(hKey, L"Path", 0, NULL, (LPBYTE)buffer, &bufferSize);
if (queryVal == ERROR_SUCCESS)
{
//Access violation error here; I need some type of conversion.
value = buffer;
}
}
No posts that I've read on here so far have led me to an answer. C++ is not my primary dev language.
UPDATE: None of the proposed answers worked for me. I found an alternative way to do what I needed.

Answer 1

You don't want a buffer of LPWSTR, you want a buffer of wchar_t. A pointer to that will be LPWSTR as it's a typedef for wchar_t *.
These two lines from WinNT.h are relevant:
typedef wchar_t WCHAR; // wc, 16-bit UNICODE character
typedef __nullterminated WCHAR *NWPSTR, *LPWSTR, *PWSTR;
Edit: I suspect the problem is with the part of the code you haven't shown us. Are you returning value from a function? If so then the problem is that you're returning a pointer to a buffer that has gone out of scope and been destroyed. I would return a std::wstring or CString instead.

Answer 2

Your buffer variable is declaring an array of 512 wchar_t* pointers when it should be declaring an array of 512 wchar_t characters instead. The first commented-out line of code is the correct code to use:
WCHAR buffer[512];
DWORD bufferSize = sizeof(buffer);
ULONG queryVal = RegQueryValueExW(hKey, L"Path", 0, NULL, (LPBYTE)buffer, &bufferSize);
if (queryVal == ERROR_SUCCESS)
{
//...
}
Keep in mind that the buffer will not be null-terminated if the Registry value was not stored with its own null-terminator, so you should allocate some extra space for your own null terminator, just in case:
WCHAR buffer[512+1];
DWORD bufferSize = (sizeof(buffer) - sizeof(WCHAR));
LONG queryVal = RegQueryValueExW(hKey, L"Path", 0, NULL, (LPBYTE)buffer, &bufferSize);
if (queryVal == ERROR_SUCCESS)
{
buffer[bufferSize / sizeof(WCHAR)] = 0;
//...
}
Alternatively, use RegGetValue() instead, which handles the null terminator for you:
WCHAR buffer[512+1];
DWORD bufferSize = sizeof(buffer);
LONG queryVal = RegGetValueW(hKey, NULL, L"Path", RRF_RT_REG_SZ | RRF_RT_REG_EXPAND_SZ, NULL, buffer, &bufferSize);
if (queryVal == ERROR_SUCCESS)
{
//...
}