一个简单的日志函数C++

有时候程序总是会发生意想不到的情况，为了方便排查错误的情况，还是写日志比较方便。这里自己写了一个简单的函数，能实现基本的功能。

BOOL WriteLog(char * DataBuffer)

{
    CString strTempPath;
    ::GetTempPath(MAX_PATH, strTempPath.GetBuffer(MAX_PATH));
    CString strLogFile = strTempPath + L"Log.txt";
    HANDLE hFile = INVALID_HANDLE_VALUE;
    DWORD dwBytesWritten = 0;
    BOOL bErrorFlag = FALSE;
    OVERLAPPED strOverlapped = {};
    strOverlapped.Offset = 0xFFFFFFFF;
    strOverlapped.OffsetHigh= 0xFFFFFFFF;
    hFile = CreateFile(strLogFile, GENERIC_READ| GENERIC_WRITE, 0, NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
    if (hFile== INVALID_HANDLE_VALUE)
    {
        return false;
    }
    char TimeMessage[MAX_PATH] = { 0 };
    SYSTEMTIME st;
    ::GetLocalTime(&st);
    char szTime[26] = { 0 };
    sprintf_s(szTime, "%04d-%02d-%02d %02d:%02d:%02d %d ", st.wYear, st.wMonth, st.wDay, st.wHour, st.wMinute, st.wSecond, st.wMilliseconds);
    sprintf_s(TimeMessage, "%s: %s
", szTime,DataBuffer);
    DWORD dwBytesToWrite = (DWORD)strlen(TimeMessage);
    bErrorFlag = WriteFile(hFile, TimeMessage, dwBytesToWrite, NULL, &strOverlapped);
    if (bErrorFlag==FALSE)
    {
        return false;
    }
    CloseHandle(hFile);
    return true;
}

这里用到CreateFile和WriteFile函数：

CreateFile 函数创建或打开下列对象，并返回一个可以用来访问这些对象的句柄。 
  文件 
  pipes
  邮槽 
  通信资源 
  磁盘驱动器（仅适用于 windowsNT ） 
  控制台 
  文件夹（仅用于打开）

HANDLE CreateFile(
 LPCTSTR lpFileName,    // 指向文件名的指针 
 DWORD dwDesiredAccess,    // 访问模式（写 / 读） 
 DWORD dwShareMode,    // 共享模式 
 LPSECURITY_ATTRIBUTES lpSecurityAttributes, // 指向安全属性的指针 
 DWORD dwCreationDisposition,   // 如何创建 
 DWORD dwFlagsAndAttributes,   // 文件属性 
 HANDLE hTemplateFile    // 用于复制文件句柄 
);
BOOL WriteFile(
  HANDLE       hFile,
  LPCVOID      lpBuffer,
  DWORD        nNumberOfBytesToWrite,
  LPDWORD      lpNumberOfBytesWritten,
  LPOVERLAPPED lpOverlapped
);

这里有一点需要说明的，要写让文件能追加改写，一定要定义一个 OVERLAPPED 结构体，并把offset,offsethigh设成0xFFFFFFFF，并把这个结构体的地址传给WriteFile的最后一个参数。不然每次都会重头写，

 OVERLAPPED strOverlapped = {};
 strOverlapped.Offset = 0xFFFFFFFF;
 strOverlapped.OffsetHigh= 0xFFFFFFFF;
 bErrorFlag = WriteFile(hFile, TimeMessage, dwBytesToWrite, NULL, &strOverlapped);

这里有一个获得time的函数，也值得关注。

 SYSTEMTIME st;
 ::GetLocalTime(&st);
 char szTime[26] = { 0 };
 sprintf_s(szTime, "%04d-%02d-%02d %02d:%02d:%02d %d ", st.wYear, st.wMonth, st.wDay, st.wHour, st.wMinute, st.wSecond, st.wMilliseconds)

最后的结果类似这样的：