[Qt] 文本文件读写， 摘自官方文档

Reading Files Directly

The following example reads a text file line by line:

    QFile file("in.txt");
    if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
        return;

    while (!file.atEnd()) {
        QByteArray line = file.readLine();
        process_line(line);
    }

The QIODevice::Text flag passed to open() tells Qt to convert Windows-style line terminators ("rn") into C++-style terminators ("n"). By default,QFile assumes binary,i.e. it doesn‘t perform any conversion on the bytes stored in the file.

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Using Streams to Read Files

The next example uses QTextStream to read a text file line by line:

    QFile file("in.txt");
    if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
        return;

    QTextStream in(&file);
    while (!in.atEnd()) {
        QString line = in.readLine();
        process_line(line);
    }

QTextStream takes care of converting the 8-bit data stored on disk into a 16-bit Unicode QString. By default,it assumes that the user system‘s local 8-bit encoding is used (e.g.,ISO 8859-1 for most of Europe; see QTextCodec::codecForLocale() for details). This can be changed using setCodec().

To write text,we can use operator<<(),which is overloaded to take a QTextStream on the left and various data types (including QString) on the right:

    QFile file("out.txt");
    if (!file.open(QIODevice::WriteOnly | QIODevice::Text))
        return;

    QTextStream out(&file);
    out << "The magic number is: " << 49 << "n";