c++ - 为什么 WinAPI FormatMessage 失败，总是返回 false

Question

我正在尝试从 FormatMessage 方法获取错误消息，但该方法总是返回 false 并且 lpBuffer 为空。

我想知道我做错了什么？

谢谢

LPTSTR lpBuffer = NULL;
DWORD dwError = GetLastError();
int nResult = 0;
if (dwError >= 12000 && dwError <= 12174)
{
    logger.info("dwError >= 12000 && dwError <= 12174");
    nResult = FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_HMODULE, GetModuleHandle("wininet.dll"), dwError, 0, lpBuffer, 0, NULL);
}
else
{
    logger.info("in else");
    nResult = FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS, NULL, dwError, MAKELANGID(LANG_ENGLISH, SUBLANG_ENGLISH_US),lpBuffer, 0, NULL);
}

if (nResult)
{
    logger.critical("Cannot start Drools client [" + m_exe + "] because [" + lpBuffer + "]");
    //wcout << (LPWSTR)lpBuffer << endl;
    LocalFree(lpBuffer);
}
else
{
    logger.critical("Cannot start Drools client [" + m_exe + "] because [ Windows error code : " + boost::lexical_cast<string>(dwError) + " ]");
}

Answer 1

你说错了。如果您传递 FORMAT_MESSAGE_ALLOCATE_BUFFER，则必须为其提供存储缓冲区的位置，因此“您必须将指针转换为 LPTSTR(例如，(LPTSTR)&lpBuffer)。 "

即:

nResult = FormatMessage(
    FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_HMODULE,
    GetModuleHandle("wininet.dll"), 
    dwError, 
    0, 
    (LPTSTR)&lpBuffer, 
    BUFFER_SIZE, 
    NULL
);

请参阅此处的文档:

• http://msdn.microsoft.com/en-us/library/windows/desktop/ms679351(v=vs.85).aspx