How to nicely “cast” qint64 to int for QProgressBar

问题

I'm playing around with QFtp (yes .. I know) and all works well.

Using code from their own example(s) as a guideline.

http://doc.qt.io/archives/qt-4.7/network-qftp-ftpwindow-cpp.html

The only problem I'm having is when sending (or receiving) big files (let's say 3 GB) the progress bar glitches out.

This is due to the cast from qint64 to int in:

void FtpWindow::updateDataTransferProgress(qint64 readBytes, 
    qint64 totalBytes) 
{
    progressDialog->setMaximum(totalBytes);
    progressDialog->setValue(readBytes);
}

I'm wondering what would be the nicest way to handle this after googling for about an hour and settling on keeping it 'safe' by making sure I don't go out of range.

while (totalBytes > 4294967295UL)
{ 
   totalBytes = totalBytes/4294967295UL;
   readBytes = readBytes/4294967295UL;
}

But that doesn't "feel" right . .

回答1:

You can make the progress bar present the progress as a percentage:

void FtpWindow::updateDataTransferProgress(qint64 readBytes, 
    qint64 totalBytes) 
{
    progressDialog->setMaximum(100);
    progressDialog->setValue((qint)((readBytes * 100) / totalBytes));
}

回答2:

Set your progress bar to a range of 0-100, and display the percentage of bytes read instead of trying to set the absolute value.

来源：https://stackoverflow.com/questions/4931780/how-to-nicely-cast-qint64-to-int-for-qprogressbar