Problem with screen update...

[yop]

//Pseodu
int i=0;
while(!eof(fptr){
    ReadBuff(fptr,Buff,SIZE);
    WriteToPrintf(Buff,SIZE);
    ProgressBarUpdate(i);
    qApp->processEvents(); // This will make your app responcive
    i+=IncrementValue;
}

//Pseodu
int i=0;
while(!eof(fptr){
    ReadBuff(fptr,Buff,SIZE);
    WriteToPrintf(Buff,SIZE);
    ProgressBarUpdate(i);
    qApp->processEvents(); // This will make your app responcive
    i+=IncrementValue;
}

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Kepp SIZE small.
But moving it to a new thread is the best solution.