Win32编程TextOut WM_Paint

Question

Having some trouble in this block of code at the TextOut line it says:

error: cannot convert 'std::string* {aka std::basic_string<char>*}' to 
'LPCSTR {aka const char*}' for argument 4 to 
'BOOL TextOutA(HDC, int, int, LPCSTR, int)'

I've searched for a while and wasn't able to find anything that didn't either eternally confuse me or would accomplish what I want to do which is draw a string.

case WM_PAINT:
        {
            HDC hdc;
            PAINTSTRUCT ps;
            string text = "Something";

            RECT rect;
            GetClientRect( hwnd, &rect );
            hdc = BeginPaint( hwnd, &ps );

            TextOut( hdc, rect.right/2, rect.bottom/2, &text, 1 );

            EndPaint( hwnd, &ps );
        }
        return 0;
        break;

Answer 1

You need to pass a pointer to a char array, not a C++ string. Try:

TextOut( hdc, rect.right/2, rect.bottom/2, text.c_str(), 1 );

Note that you've requested it to output only one character.

Answer 2

The error message explains what the problem is:

The LPCSTR type is a typedef (alias for) const char * . This is a C-style pointer, which is what the constant string "Something" defaults to (but not text ).

The std::string type is a typedef (alias for) std::basic_string<char> . This is a C++ template class that is used to manage strings dynamically, like C#/Java strings, or the CString type from MFC/ATL.

The &text line is a pointer to the string object, not a pointer to the string itself. Likewise, std::string does not provide implicit conversion to const char * . You need to explicitly call text.c_str() which is intended for use with APIs that take C-style strings.

For the last argument of TextOut , you can pass -1 to get it to calculate the length of the string (not 1 ). Alternatively, as you have the string in a std::string object, you can use text.size() .