Qt5 Tutorial QFile - 2020

In this tutorial, we will learn QFile.

The QFile class provides an interface for reading from and writing to files.

QFile is an I/O device for reading and writing text and binary files and resources. A QFile may be used by itself or, more conveniently, with a QTextStream or QDataStream.

The file name is usually passed in the constructor, but it can be set at any time using setFileName(). QFile expects the file separator to be '/' regardless of operating system. The use of other separators (e.g., '\') is not supported.

We can check for a file's existence using exists(), and remove a file using remove().

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., UTF-8 on most unix based operating systems). 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.

In the following code, we open a new file with the given name and write a text into the file. Then, we read in the file back and print the content to our console.

#include <QCoreApplication>
#include <QFile>
#include <QString>
#include <QDebug>
#include <QTextStream>

void write(QString filename)
{
    QFile file(filename);
    // Trying to open in WriteOnly and Text mode
    if(!file.open(QFile::WriteOnly |
                  QFile::Text))
    {
        qDebug() << " Could not open file for writing";
        return;
    }

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

    QTextStream out(&file;);
    out << "QFile Tutorial";
    file.flush();
    file.close();
}

void read(QString filename)
{
    QFile file(filename);
    if(!file.open(QFile::ReadOnly |
                  QFile::Text))
    {
        qDebug() << " Could not open the file for reading";
        return;
    }

    QTextStream in(&file;);
    QString myText = in.readAll();
    qDebug() << myText;

    file.close();
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QString filename = "C:/Qt/MyFile.txt";
    write(filename);
    read(filename);

    return a.exec();
}

Output:

"QFile Tutorial"