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.