Am I Incorrectly using the Windows Clipboard? - c++

Question

I have some code to copy and paste:
void WinClipboard::copy( const std::string& input )
{
LPWSTR lptstrCopy;
HGLOBAL hglbCopy;
std::wstring text;
text = _winUTF8ToUTF16(input);
// Open the clipboard, and empty it.
if (!OpenClipboard(NULL))
return;
EmptyClipboard();
// Allocate a global memory object for the text.
hglbCopy = GlobalAlloc(GMEM_MOVEABLE,
((text.length() + 1) * sizeof(WCHAR)));
if (hglbCopy == NULL)
{
CloseClipboard();
return;
}
// Lock the handle and copy the text to the buffer.
lptstrCopy = (LPWSTR)GlobalLock(hglbCopy);
memcpy(lptstrCopy, text.c_str(),
(text.length() + 1) * sizeof(WCHAR) );
lptstrCopy[(text.length() + 1) * sizeof(WCHAR)] = (WCHAR) 0; // null character
GlobalUnlock(hglbCopy);
// Place the handle on the clipboard.
SetClipboardData(CF_UNICODETEXT, hglbCopy);
// Close the clipboard.
CloseClipboard();
}
std::string WinClipboard::paste()
{
HGLOBAL hglb;
LPWSTR lptstr;
std::string result;
std::wstring input;
// get the clipboard text.
if (!IsClipboardFormatAvailable(CF_UNICODETEXT))
return result;
if (!OpenClipboard(NULL))
return result;
hglb = GetClipboardData(CF_UNICODETEXT);
if (hglb != NULL)
{
lptstr = (LPWSTR)GlobalLock(hglb);
if (lptstr != NULL)
{
GlobalUnlock(hglb);
input = lptstr;
result = _winUTF16ToUTF8(input);
}
CloseClipboard();
}
return result;
}
It works great except, when I quickly do CTRL C then CTRL-V (essentially calling the above copy and paste functions) the entire application freezes.
Am I forgetting to check for something or forgetting to release a resource?

Answer 1

I see two problems in your paste() function:
1) it is calling GlobalUnlock() before assigning the clipboard data to your std::wstring variable. You need to reverse those operations - call GlobalUnlock() after copying the data, not before.
2) it is not calling CloseClipboard() if GetClipboardData() fails.

Answer 2

Another "problem".
In the copy function:
The line
lptstrCopy[(text.length() + 1) * sizeof(WCHAR)] = (WCHAR) 0;
should be
lptstrCopy[text.length() + 1] = (WCHAR) 0;
to avoid the overflow/heap corruption.