FormatMessageWrapper.h

// sktoolslib - common files for SK tools

// Copyright (C) 2012, 2017, 2020-2021 - Stefan Kueng

// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software Foundation,
// 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
//

#pragma once

/**
 * A wrapper class for calling the FormatMessage() Win32 function and controlling
 * the lifetime of the allocated error message buffer.
 */

class CFormatMessageWrapper
{
private:
    LPWSTR buffer;
    DWORD  result;
    void   release();
    void   obtainMessage() { obtainMessage(::GetLastError()); }
    void   obtainMessage(DWORD errorCode);

public:
    CFormatMessageWrapper()
        : buffer(nullptr)
        , result(0)
    {
        obtainMessage();
    }
    CFormatMessageWrapper(DWORD lastError)
        : buffer(nullptr)
        , result(0)
    {
        obtainMessage(lastError);
    }
    ~CFormatMessageWrapper() { release(); }
    operator LPCWSTR() const { return buffer; }
    operator bool() const { return result != 0; }
    bool     operator!() const { return result == 0; }
    LPCWSTR  c_str() const { return buffer; }
};

inline void CFormatMessageWrapper::obtainMessage(DWORD errorCode)
{
    // First of all release the buffer to make it possible to call this
    // method more than once on the same object.
    release();
    result = FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
                               FORMAT_MESSAGE_FROM_SYSTEM |
                               FORMAT_MESSAGE_IGNORE_INSERTS,
                           nullptr,
                           errorCode,
                           MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), // Default language
                           reinterpret_cast<LPWSTR>(&buffer),
                           0,
                           nullptr);
}

inline void CFormatMessageWrapper::release()
{
    if (buffer != nullptr)
    {
        LocalFree(buffer);
        buffer = nullptr;
    }

    result = 0;
}