WCHAR to LPCWSTR

Question

when i use CreateFile function like below ...it gives me valid handle

HANDLE hDevice = CreateFile (TEXT("\\\\.\\G:"),
                 0,FILE_SHARE_READ | FILE_SHARE_WRITE, // share mode
                 NULL, OPEN_EXISTING, 0, NULL);

if( hDevice == INVALID_HANDLE_VALUE )
{
  qDebug()<<"In valid handle";
}
else
{
  qDebug()<<"valid handle";
}

when i use like below ...it gives me invalid handle..

WCHAR Drive[4];

qDebug ()<<QString::fromWCharArray ( Drive ); 

The above prints like "G:\"

HANDLE hDevice = CreateFile ( Drive,
                 0,FILE_SHARE_READ | FILE_SHARE_WRITE, // share mode
                 NULL, OPEN_EXISTING, 0, NULL);

if( hDevice == INVALID_HANDLE_VALUE )
{
  qDebug()<<"In valid handle";
}
else
{
  qDebug()<<"valid handle";
}

How can i change the wchar to LPCWSTR

Thank you

Answer 1

The problem is not the conversion of the string, but the contents of the string. You can't open a volume (I guess that's what you're trying to do) with "G:\". It needs to be in the same format as you used in the first example. From MSDN:

When opening a volume or floppy drive, the lpFileName string should be the following form: \\.\X:. Do not use a trailing backslash, which indicates the root directory of a drive.

Hint: Always use GetLastError() after API functions fail to get the reason for the failure.

Update: MSDN Link

Answer 2

You can either use the toWCharArray function or try something like this:

handle = CreateFile((LPCWSTR) fileName.constData(), FILE_SHARE_READ | FILE_SHARE_WRITE, 0, OPEN_EXISTING, 0, 0);

or this:

handle = CreateFile((LPCWSTR) fileName.utf16(), FILE_SHARE_READ | FILE_SHARE_WRITE, 0, OPEN_EXISTING, 0, 0);

Answer 3

LPCWSTR is a pointer (LP) to a constant (C) wide character (W) string (STR). In other words, this is a const WCHAR*

WCHAR Drive[4]; is a wide character array, which can also be called a wide character string.

Any array of a certain type can implicitly convert to a pointer to that same type. Furthermore, a pointer of a certain type can implicitly convert to a constant pointer of the same type, especially in the case of a function call.

Thus passing Drive to that function implicitly converts to LPCWSTR.

Your problem in not in that conversion. Your problem is most likely in the contents of your strings, as humbagumba's answer already explained.