本文测试了ReadDirectoryChangesW 类监控文件变化。

#include<iostream> 
#include<string>
#include<Windows.h>
using namespace std;

string  WStringToString(const std::wstring &wstr);
void RunWatchFile()
{
    string watchDirectory = "E:/Test";
    HANDLE hDirectory = CreateFile(watchDirectory.c_str(),
                        GENERIC_READ | GENERIC_WRITE | FILE_LIST_DIRECTORY,
                        FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
                        NULL,
                        OPEN_EXISTING,
                        FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OVERLAPPED,
                        NULL);
    if (hDirectory == INVALID_HANDLE_VALUE)
    {
        DWORD dwErr = GetLastError();
        return;
    }

    char notify[1024];
    memset(notify, 0, sizeof(notify));
    FILE_NOTIFY_INFORMATION *pNotification = (FILE_NOTIFY_INFORMATION *)notify;
    DWORD bytesReturned = 0;

    while (TRUE)
    {
        ZeroMemory(pNotification, sizeof(notify));

        auto watchState = ReadDirectoryChangesW(hDirectory,
            &notify,
            sizeof(notify),
            TRUE,   //监控子目录
            FILE_NOTIFY_CHANGE_FILE_NAME | FILE_NOTIFY_CHANGE_LAST_WRITE, 
            (LPDWORD)&bytesReturned,
            NULL,
            NULL);

        if (GetLastError() == ERROR_INVALID_FUNCTION)
        {
            cout << "文件监控，系统不支持 " << watchDirectory << endl;
            break;
        }
        else if (watchState == FALSE)
        {
            DWORD dwErr = GetLastError();
            cout << "文件监控，监控失败 " << watchDirectory << dwErr << endl;
            break;
        }
        else if (GetLastError() == ERROR_NOTIFY_ENUM_DIR)
        {
            cout << "文件监控，内存溢出 " << watchDirectory <<endl;
            continue;
        }
        else
        {
            //检测返回的信息
            wstring fileName(pNotification->FileName, pNotification->FileNameLength / sizeof(wchar_t));
            std::string fullFileName = watchDirectory + "/" +  WStringToString(fileName);          
            if (pNotification->Action == FILE_ACTION_ADDED)
            {
                cout << "文件监控，新增文件 " << fullFileName  << endl;
            }
            else if (pNotification->Action == FILE_ACTION_REMOVED)
            {
                cout << "文件监控，删除文件 " << fullFileName << endl;
            }
            else if (pNotification->Action == FILE_ACTION_MODIFIED)
            {
                cout << "文件监控，修改文件 "  << fullFileName << endl;
            }
            else if (pNotification->Action == FILE_ACTION_RENAMED_OLD_NAME)
            {
                cout << "文件监控，重命名文件 " << fullFileName << endl;
            }
            //PostMessage通知主线程
        }
    }
    CloseHandle(hDirectory);
}

string  WStringToString(const std::wstring &wstr)
{
    string result;
    //获取缓冲区大小，并申请空间，缓冲区大小事按字节计算的  
    int len = WideCharToMultiByte(CP_ACP, 0, wstr.c_str(), wstr.size(), NULL, 0, NULL, NULL);
    char* buffer = new char[len + 1];
    //宽字节编码转换成多字节编码  
    WideCharToMultiByte(CP_ACP, 0, wstr.c_str(), wstr.size(), buffer, len, NULL, NULL);
    buffer[len] = '\0';
    //删除缓冲区并返回值  
    result.append(buffer);
    delete[] buffer;
    return result;
}

int main()
{
    RunWatchFile();
    getchar();
    return 0;
}

  上例中监控的目录是“E:\\Test”，在此目录下创建txt文件，命名为“log.txt”。

   运行结果：