Writing to a file

[ShahriarNK]

void Add::saveData()
{
    QFile file("c://WeightTracker.csv");
    if (!file.open(QIODevice::WriteOnly)) {
        //std::cerr << "Cannot open file for writing: "
                  //<< qPrintable(file.errorString()) << std::endl;
        return;
    }

    QTextStream out(&file);
    qint32 weight = (ui->lineEdit->text()).toInt();
    QString date_of_weight = (ui->dateEdit->date()).toString();

    out << date_of_weight << "," << weight << endl;


}

I am using the above function to write to a file (the application is a nokia mobile application). It works correctly and writes a single line to the file.
But I have 2 problems:
1. The data is written when a button is clicked (saveData is a slot connected to a clicked signal). But when I click the button multiple times, the first line is always overwritten (so there is always only 1 row in the file). With every button click, I want new data to be added as a new row.

2. If I enable the following line:

//std::cerr << "Cannot open file for writing: "
                  //<< qPrintable(file.errorString()) << std::endl;

I get the following error: "cerr is not a member of std"; can you please help me resolve this error?

The project can be found here: [link removed]

Thanks in advance for your help.

[danhicksbyron]

Try
open(QIODevice::WriteOnly | QIODevice::Append)

[dahiya.vinod]

Yes, open file in append mode. If you frequently need to write into file,instead of opening file every time you can keep it open untill you are done with it.

[ShahriarNK]

Thankyou both for your solution; it works perfectly.

Does any one have any clue regarding the second error i am facing:

2. If I enable the following line:

//std::cerr << "Cannot open file for writing: "
                  //<< qPrintable(file.errorString()) << std::endl;

I get the following error: "cerr is not a member of std"; can you please help me resolve this error?

[dahiya.vinod]

Did you include <iostream> header?
you should use qt specific things like qDebug(), qWarning(), qFatal(),qCritical(), equivalent for your code is:

qDebug() << "Cannot open file for writing: " << qPrintable(file.errorString());