Why _wtof Function Does Not Work?

Question

      I am creating a basic application that has two text fields, and I am using the function SendMessage with the corresponding arguments to store the text in two buffers. Everything works fine. The SendMessage returns the string. However, I want to convert the wide-character strings into doubles, so I use _wtof function. But the function returns a bad value. I do not wnt to use atof because the strings are Unicode.
     Also, how can I read the zero from the string and store those into the double variable?

     Here some code:

TCHAR szBuffer1[100], szBuffer2[100];

SendMessage (hwndControl, EM_GETLINE, 3, (LPARAM) szBuffer1);
speed = _wtof (szBuffer1);
value = wsprintf (szBuffer2, TEXT ("%d"), speed);
MessageBox (NULL, szBuffer2, TEXT ("Message"), MB_ICONERROR) ;

     Thanks in advance!

Answer 1

I think _wtof is working fine, and you have the wrong type specifier in your wsprintf call. %d indicates an integer, you should be using %f or some other double type specifier.

Answer 2

In addition to ildjarn's reply, you are inconsistent in your character usage.
_wtof and wsprintf is wide character functions, but you are passing them TCHARs.

In MBCS, your code won't compiler.  Should be...

speed = _ttof(szBuffer1);
_stprintf(szBuffer2, _T("%f"), speed);

Answer 3

In addition to the above, I would recommend you use StringCchPrintf instead of _stprintf because the latter is an unsafe function. You cannot specify a buffer length, so it can easily be overrun.

Answer 4

     Thanks!

     You were right. I was using a bad type identifier in wprintf. Always, I tried to read the double. It returned a zero. 

Answer 5

You aren't initializing szBuffer1 properly. From the EM_GETLINE documentation: "Before sending the message, set the first word of this buffer to the size, in TCHARs, of the buffer. For ANSI text, this is the number of bytes; for Unicode text, this is the number of characters. The size in the first word is overwritten by the copied line."

There's probably a better way to do it, but you can try this:

TCHAR szBuffer1[100] = { };

*reinterpret_cast<WORD*>(&szBuffer1[0]) = 100;

TCHAR szBuffer2[100] = { };

SendMessage(hwndControl, EM_GETLINE, 3, (LPARAM)szBuffer1);

speed = _ttof(szBuffer1);

value = _stprintf(szBuffer2, _T("%f"), speed);

MessageBox (0, szBuffer2, _T("Message"), MB_ICONERROR);