File locking in Windows

FileLocker.hpp

#pragma once
#ifndef FILELOCKER_H
#define FILELOCKER_H

#include <Windows.h>
#include <string>
#include <tchar.h>
#include <iostream>

#if UNICODE
typedef std::wstring tstring;
#define tcout std::wcout
#else
typedef std::string tstring;
#define tcout std::cout
#endif // UNICODE

enum class FileLockModes
{
    AllowReading,
    AllowWriting,
    AllowDeletion
};

class FileLocker
{
    tstring m_tsFileToLock;
    HANDLE m_hLockedFileHandle;
    DWORD m_dwLastError;
    bool m_bSharingViolation;
public:
    FileLocker(tstring& fileToLock) :
        m_tsFileToLock(fileToLock),
        m_hLockedFileHandle(nullptr),
        m_dwLastError(ERROR_SUCCESS),
        m_bSharingViolation(false)
    {
    }
    bool LockFile(FileLockModes);
    bool UnLockFile();
    auto GetLastErrorCode() { return m_dwLastError; }
};

bool FileLocker::LockFile(FileLockModes lockMode)
{
    auto fileSharingMode = FILE_SHARE_READ;
    switch (lockMode)
    {
        case FileLockModes::AllowReading:
            break;
        case FileLockModes::AllowWriting:
            fileSharingMode = FILE_SHARE_WRITE;
            break;
        case FileLockModes::AllowDeletion:
            fileSharingMode = FILE_SHARE_DELETE;
            break;
        default:
            tcout << _T("Invalid mode specified; Will not attempt to lock file.");
            return false;
    }
    m_hLockedFileHandle = ::CreateFile(m_tsFileToLock.c_str(),
        GENERIC_READ | GENERIC_WRITE,
        fileSharingMode,
        nullptr,
        OPEN_EXISTING,
        0,
        nullptr);
    auto bRet = (INVALID_HANDLE_VALUE != m_hLockedFileHandle);
    if (bRet)
    {
        tcout << _T("File:  ") << m_tsFileToLock << _T(" locked successfully.\n");
    }
    else
    {
        m_dwLastError = ::GetLastError();
        if (ERROR_SHARING_VIOLATION == m_dwLastError)
        {
            m_bSharingViolation = true;
            tcout << _T("ERROR_SHARING_VIOLATION; File is already in use by another process.\n");
        }
    }
    return bRet;
}

bool FileLocker::UnLockFile()
{
    auto bRet = false;
    if (m_hLockedFileHandle)
    {
        bRet = static_cast<bool>(::CloseHandle(m_hLockedFileHandle));
        if (bRet)
        {
            m_dwLastError = ERROR_SUCCESS;
            m_hLockedFileHandle = nullptr;
        }
        else
        {
            m_dwLastError = ::GetLastError();
        }
    }
    return bRet;
}
#endif // !FILELOCKER_H