how to specify variable file name?

[aurora]

hello everyone....
i'm opening a file as shown below....
how can I specify variable file name......different time, user may give different file name.....
When i'm trying to change the following format, i got error....
Please help me

QFile file(":/input.txt");
 
if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
return;
ui->label_4->setText("FILE NAME:"+filename);
while (!file.atEnd())
{
 
//DOING REST OPERATION...
}

QFile file(":/input.txt");

if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
return;
ui->label_4->setText("FILE NAME:"+filename);
while (!file.atEnd())
{

//DOING REST OPERATION...
}

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