API Windows WriteFile: works but returns 0

[KrProg91]

Hello
I wrote a method that does nearly well it's job (except it returns an error) : The function write an image file to a USB key partition with the function WriteFile. The USB key is well formated with the image file but WriteFile returns 0 (false) and the written Bytes stay at 0,
I use QT for reading the file and because of the rest of the code was not made by me, I must use win32 lib .
the read file contains a lot of "\0"

boolean MyClass::writeFromFile(QString filepath)
{
    Log *log = Log::getInstance();
    qDebug() << "Openning file " << filepath;
    QFile file(filepath);
    if (!file.open(QIODevice::ReadOnly))
    {
        qDebug() << "Error: File "<< filepath << " not found";
        log->info("Error: File " + filepath + " not found");
        return false;
    }

    qDebug() << "File "<< filepath << " found";
    log->info("File " + filepath + " found");

    QByteArray buffer = file.readAll();
    file.close();

    openBatDevice();
    int retData = SetFilePointer(_batDevice, 0, NULL, FILE_BEGIN);
    if (retData == 0xFFFFFFF)
    {
        qDebug() << "Error: SetFilePointer is 0xFFFFFFF";
        log->info("Error: SetFilePointer is 0xFFFFFFF");
        return false;
    }

    DWORD nbOfByteWr;
    LPDWORD nNumberOfBytesToWrite;

    BYTE* data = (BYTE*) buffer.data();

    DWORD dwLen = strlen(buffer.data());


    DWORD dwBytesRead = (DWORD) buffer.size();

    qDebug() << "INFO buffer data: " << buffer.data();
    qDebug() << "INFO buffer size: " << buffer.size();


    BOOL out = WriteFile(_batDevice, data, dwBytesRead, &nbOfByteWr, NULL);

    qDebug() << "INFO out: " << out;

    qDebug() << "INFO nbOfByteWr: " << nbOfByteWr;


    int errorId = (int) GetLastError();
    qDebug() << "Error WriteSector : " + QString::number(errorId);
    qDebug() << "Error WriteSector : " + errorId;



}

Returns:

Openning file  "C:/Users/user/Documents/Projet/Project/Outils_project/projectExe/debug/clef_XXX.img"
File  "C:/Users/user/Documents/Projet/Project/Outils_project/projectExe/debug/clef_XXX.img"  found
INFO buffer data:  
INFO buffer size:  4198400
INFO out:  0
INFO nbOfByteWr:  0
Error WriteSector : 
Error WriteSector : 

ReadFile(_batDevice, buffer, toRead, &read, NULL)

News:

Here is how the Handle is made

_batDevice = CreateFile(devicePath, GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, 0, NULL);

In the documentation [URL="https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-createfilea"]https://docs.microsoft.com/...[/URL] I read we need to use the flag FILE_FLAG_OVERLAPPED for beeing Asynchronous , so I anderstand it is synchronous, isn't it?



Thanks a lot

[kbw]

The write didn't work, it returned FALSE.

[KrProg91]

Yes and no :
Yes: because the USB key is well written (the written data are good)
No: WriteFile returns FALSE, and I don't know why

[Thomas1965]

Yes and no :

That's a contradiction. 0 bytes written, return value false means clearly WriteFile didn't work.
Maybe the written data was there before.
Delete it and run the code again.

WriteFile returns FALSE, and I don't know why

To get an error msg you can use this code:

std::string GetLastWinError ()
{
  LPVOID lpMsgBuf;
  LPVOID lpDisplayBuf;
  DWORD dw = GetLastError ();

  FormatMessage (FORMAT_MESSAGE_ALLOCATE_BUFFER |FORMAT_MESSAGE_FROM_SYSTEM, 
  NULL, dw,  MAKELANGID (LANG_NEUTRAL, SUBLANG_DEFAULT), (LPTSTR)&lpMsgBuf,  0, NULL);

  std::ostringstream oss;
  oss << "Windows Error ";
  oss << dw << " :" << (LPCSTR)lpMsgBuf;

  LocalFree (lpMsgBuf);

  return oss.str();

[kbw]

WriteFile returns FALSE, and I don't know why

That's what GetLastError() is for.