Calculate MD5 sum of a big file

[realdarkman71]

Hi all,

I need a md5 sum of a file with a big size. I found this:

QFile file("/home/chris/backup.img");
 
    if (file.open(QIODevice::ReadOnly)) {
        QByteArray fileData = file.readAll();
        QByteArray hashData = QCryptographicHash::hash(fileData, QCryptographicHash::Md5);
 
        qDebug() << hashData.toHex();
    }

QFile file("/home/chris/backup.img");

    if (file.open(QIODevice::ReadOnly)) {
        QByteArray fileData = file.readAll();
        QByteArray hashData = QCryptographicHash::hash(fileData, QCryptographicHash::Md5);

        qDebug() << hashData.toHex();
    }

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but with a file size > 8 GB it's a memory overkill!

Are there any other methods?

Thanks!
Chris

[Talei]

QCryptographicHash::hash() is static "helper" function, and what You are looking for is QCryptographicHash::addData().

This was answered here i.e. http://www.qtcentre.org/threads/3567...an-entire-file

[realdarkman71]

That works, thanks for the hint!

Is there a way to calculate md5 sum from a dvd (/dev/cdrom) with this method? It musts read the dvd raw data, not files on disc!

[ChrisW67]

Open and read the /dev/cdrom device directly: you get the bytes from one end of the disc to the other.

[realdarkman71]

How? QFile doesn't work!

[ChrisW67]

Sure it does, but QIODevice::atEnd() is not reliable on block special files so you have to adopt a slightly different approach:

QFile in("/dev/cdrom");
if (in.open(QIODevice::ReadOnly)) {
  qDebug() << "Opened ok";
  char buf[2048];
  int bytesRead;
  while ((bytesRead = in.read(buf, 2048)) > 0) {
    qDebug() << "Read" << bytesRead;
  }
  qDebug() << "Final bytesRead value" << bytesRead;
  in.close();
}

QFile in("/dev/cdrom");
if (in.open(QIODevice::ReadOnly)) {
  qDebug() << "Opened ok";
  char buf[2048];
  int bytesRead;
  while ((bytesRead = in.read(buf, 2048)) > 0) {
    qDebug() << "Read" << bytesRead;
  }
  qDebug() << "Final bytesRead value" << bytesRead;
  in.close();
}

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This will fail to open if there is no disc in the drive. In a real program you would use a larger buffer, distinguish between bytesRead == 0 and -1 etc.

[realdarkman71]

Thanks for the hint, but it doesn't work for me! The md5 sum from image and dvd are not the same! On command line they are identical! Or is the code wrong?

QCryptographicHash hash(QCryptographicHash::Md5);
QFile in("/dev/cdrom");
 
if (in.open(QIODevice::ReadOnly)) {
    char buf[2048];
 
    while (in.read(buf, 2048) > 0) {
        hash.addData(buf, 2048);
    }
 
    in.close();
    qDebug() << hash.result().toHex();
}
else {
    qDebug() << "Failed to open device!";
}

QCryptographicHash hash(QCryptographicHash::Md5);
QFile in("/dev/cdrom");

if (in.open(QIODevice::ReadOnly)) {
    char buf[2048];

    while (in.read(buf, 2048) > 0) {
        hash.addData(buf, 2048);
    }

    in.close();
    qDebug() << hash.result().toHex();
}
else {
    qDebug() << "Failed to open device!";
}

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[wysota]

How many bytes did you manage to read from the device?

[realdarkman71]

...the while loop reads all data from dvd!?

[wysota]

...the while loop reads all data from dvd!?

Was this supposed to be an answer to my question? If so, then it's not what I expected. I expected that you will change your code to count how many bytes were really read, not that you expect the loop to read "all" the data.

[realdarkman71]

Ok, but how? ...sorry!