Progressbar Range and position, how to handle big numbers in C++? - c++

Question

Trying to implement windows Progressbar showing progress of download in bytes with big numbers, but am unable to do it correctly.
For a download of 2.5gb if I do following, it ends short of the full range when download is complete.
double dlSize = getDlSize();
unsigned int pbRange = (unsigned int)( dlSize / 3000 );
SendMessage( hProgressbar, PBM_SETRANGE, 0, MAKELPARAM( 0, pbRange ) );
and then set new position at each download callback as :
double dlBytes = bytesDownloaded();
unsigned int newIncrement = (unsigned int)( dlBytes / 3000 );
SendMessage( hProgressbar, PBM_DELTAPOS, (WPARAM)newIncrement, 0 );
This is a very noobish implementation, and I don't want fall in the xy situation, So my question is what is the correct way to implement a progressbar with big numbers in tune of 2-5GBs in bytes ?
I tried both approaches suggested below by #msandiford and #NikBougalis, by taking the width of the progressbar in account and by using percentage instead of actual number, I even combined both, but in all cases the newIncrement always comes out 0, maybe that's because dlSize is always lower( in double newIncrement comes out something like 1.15743e+007, type cast it and its 0 ).
What else I can do ?
New Code combining both approaches:
EDIT 2:
Added few checks to the code as I was constantly getting 0 for newIncrement, looks like its working now, not sure how well:
GetClientRect(hProgressbar, &pbRCClient);
pbWidth = pbRCClient.right - pbRCClient.left; // (pbWidth its a global variable)
unsigned int pbRange = pbRCClient.right - pbRCClient.left;
SendMessage( hProgressbar, PBM_SETRANGE, 0, MAKELPARAM( 0, pbRange ) );
and while updating :
double dlSize = getDlSize();
double doubleIncrement = ( ( dlSize * pbWidth ) / totalSize );
unsigned int newIncrement;
if ( (unsigned int)doubleIncrement < 1 )
{
blockFill += doubleIncrement;
if ( (unsigned int)blockFill > 1 )
{
newIncrement = ( unsigned int )blockFill;
SendMessage( hProgressbar, PBM_DELTAPOS, (WPARAM)newIncrement, 0 );
blockFill = 0;
}
}
else
{
newIncrement = ( unsigned int )( doubleIncrement );
SendMessage( hProgressbar, PBM_DELTAPOS, (WPARAM)newIncrement, 0 );
//blockFill = 0;
}
EDIT 3 : Looks like its still finishing early.

Answer 1

The big issue that you have is limitations in the progress bar control itself. PBM_SETRANGE is limited, and although you could use PBM_SETRANGE32 if you need to deal with values larger than 2GB you will still encounter problems.
Coincidentally, why use a double at all? Use a UINT64, which maxes out at approximately 16,384 Petabytes (if you're downloading something that will overflow that... well skip the progress bar, it will only depress you and your customers). Integers work really well for counting things like bytes.
Provided that you know the full size of the file that you are downloading, one way to work around the size of the progress bar having a limited maximum range, is to make your progress bar start at 0 and end at 100. Then you can convert the bytes received into a percentage using the simple rule of three:
percent = (bytes_received * 100) / max_bytes;
If you want to get more "granularity" you can change the scale of the progress bar to 1000 and adjust the calculation accordingly; you could even go to 10000 but at that point and depending on the width (or height) of the control, you will probably bump up against the resolution of the monitor.

Answer 2

There probably isn't much point making the progress bar more accurate than the number of pixels in progress bar window itself. Based on this, you should be able to scale the target to the number of pixels pretty easily.
RECT rcClient;
GetClientRect(hProgressBar, &rcClient);
unsigned int pbRange = rcClient.right - rcClient.left;
// Need to either keep unitsPerPixel, or recalculate later
double pixelsPerUnit = pbRange / dlSize;
SendMessage(hProgressBar, PBM_SETRANGE, 0, MAKELPARAM(0, pbRange));
Then updating progress would be something like:
double dlBytes = totalBytesDownloaded();
unsigned int newProgress = (unsigned int)(dlBytes * pixelsPerUnit);
SendMessage(hProgressBar, PBM_SETPOS, (WPARAM)newProgress, 0);
If the progress window was somehow resizeable, you would need to recalculate pbRange, reset the progress bar range and recalculate unitsPerPixel in response to a WM_SIZE message.