Working with WinAPI functions that use C-style strings as OUT parameters

Question

Given the WinAPI function that returns it, it is obtained through the OUT parameter of a C-style string, for example:

int WINAPI GetWindowTextW(
   _In_   HWND hWnd,
   _Out_  LPTSTR lpString,
   _In_   int nMaxCount
);

Is there a better way to use the function than what I do below?

HWND handle; // Assume this is initialised to contain a real window handle
std::wstring title;
wchar_t buffer[512];
GetWindowTextW(handle, buffer, sizeof(buffer));
title = buffer;

The above code works, but I have the following problems:

• The size of the buffer is completely arbitrary, since I cannot find out the length of the string returned by the function. This "feels" wrong for me - I always tried to avoid magic numbers in my code.

• If the function returns a string that is larger than the buffer, it will be truncated - this is bad!

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?

Answer 1

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Answer 2

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std::wstring GetWindowTitle(HWND hwnd) {
    std::wstring title(16, L'X');
    int cch;
    do {
      title.resize(2 * title.size());
      cch = GetWindowTextW(hwnd, &title[0], title.size());
    } while (cch + 1 == title.size());
    title.resize(cch);
    return title;
}

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