error in set UI title in MFC

Question

I am trying to change the title of an MFC window as follows:

BOOL CameraUI::OnInitDialog()
{
    // set ui title 
    TCHAR wintitle[100];
    _stprintf_s(wintitle, sizeof wintitle, _T("Camera %u"), (UINT) getSerialNumber());  
    SetWindowText(wintitle);
return TRUE;
}

When I debug I get this error at the end of the function:

Run-Time Check Failure #2 - Stack around the variable 'wintitle' was corrupted.

I am using MSVC 2008. What am I doing wrong?!

Answer 1

Do not use sizeof winTitle as-is.

The _stprintf_s function requires the number of characters, not the number of bytes.

http://msdn.microsoft.com/en-us/library/ce3zzk1k.aspx

Since obviously you're using TCHAR, then the number of characters is as follows:

sizeof(winTitle) / sizeof(winTitle[0])

or

sizeof(winTitle) / sizeof(TCHAR)

A TCHAR in the MS world is either going to be 1 byte (if the build is MBCS) or 2 bytes (which is Unicode).

Assuming you're using Unicode, by just stating sizeof winTitle, you are specifying that your array can fit a maximum of 200 characters, but that is not true (display what sizeof winTitle gives you, and you will see it is 200).

Answer 2

Use std::string and std::ostringstream instead of character buffers and sprintf. This way you can avoid buffer overruns by having these classes manage memory for you. The only time you'll need to interact with c-style strings directly is when interacting with Win32 functions.

std::ostringstream output;
std::string wintitle;
output << "Camera " << (UINT) getSerialNumber();
wintitle = output.str();
SetWindowText(wintitle.c_str());
return TRUE;

Answer 3

There is a templated overload of _stprintf_s that does not require a buffer size parameter. You can write the erroneous line as

_stprintf_s(wintitle, _T("Camera %u"), (UINT) getSerialNumber());

The template will automatically deduce the correct length of the destination buffer and protect you from passing the wrong buffer size.