Qt5 Tutorial QDir - 2020

In this tutorial, we will learn QDir.

The QDir class provides access to directory structures and their contents.

A QDir is used to manipulate path names, access information regarding paths and files, and manipulate the underlying file system. It can also be used to access Qt's resource system.

Qt uses "/" as a universal directory separator in the same way that "/" is used as a path separator in URLs. If you always use "/" as a directory separator, Qt will translate your paths to conform to the underlying operating system.

The following code checks if the two directories exist. In this example, the first one does, but the second one does not:

#include <QCoreApplication>
#include <QDir>
#include <QDebug>

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

    // forward slash for directory separator
    QDir dir1("C:/Qt");
    QDir dir2("C:/Qt/test");

    // output: true false
    qDebug() << dir1.exists() << dir2.exists();  

    return a.exec();
}

QFileInfoList QDir::drives() returns a list of the root directories on this system.

On Windows this returns a list of QFileInfo objects containing "C:/", "D:/", etc. On other operating systems, it returns a list containing just one root directory (i.e. "/").

#include <QCoreApplication>
#include <QDir>
#include <QDebug>

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

    // forward slash for directory separator
    QDir dir1("C:/Qt");
    QDir dir2("C:/Qt/test");
    qDebug() << dir1.exists() << dir2.exists();

    QDir dir3;
    foreach(QFileInfo item, dir3.drives() )
    {
        qDebug() << item.absoluteFilePath();
    }

    return a.exec();
}

Output:

true false
"C:/"
"D:/"
"E:/"

bool QDir::mkpath(const QString & dirPath) const creates the directory path dirPath.

The function will create all parent directories necessary to create the directory.

mkpath() returns true if successful; otherwise returns false.

If the path already exists when this function is called, it will return true.

The code below checks if a directory exists. In this example, a new directory will be created because it does not exist. If we run it again, the code will give a message telling the directory already exists.

#include <QCoreApplication>
#include <QDir>
#include <QDebug>
#include <QString>

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

    QString path = "C:/Qt/test";
   
    QDir dir(path);
    if(!dir.exists())
    {
        qDebug() << "Creating " << path << "directory";
        dir.mkpath(path);
    }
    else
    {
        qDebug() << path << " already exists";
    }

    return a.exec();
}

If we run the code, we get the output:

Creating  "C:/Qt/test" directory

If we run it again, we get the following message:

"C:/Qt/test"  already exists

QFileInfoList QDir::entryInfoList(const QStringList & nameFilters, Filters filters = NoFilter, SortFlags sort = NoSort) const returns a list of QFileInfo objects for all the files and directories in the directory, ordered according to the name and attribute filters previously set with setNameFilters() and setFilter(), and sorted according to the flags set with setSorting().

The name filter, file attribute filter, and sorting specification can be overridden using the nameFilters, filters, and sort arguments.

entryInfoList() returns an empty list if the directory is unreadable, does not exist, or if nothing matches the specification.

Here is the code using QDir::entryInfoList():

#include <QCoreApplication>
#include <QDir>
#include <QDebug>
#include <QString>

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

    QString path = "C:/Qt";
    QDir dir(path);

    foreach(QFileInfo item, dir.entryInfoList() )
    {
        if(item.isDir())
            qDebug() << "Dir: " << item.absoluteFilePath();
        if(item.isFile())
            qDebug() << "File: " << item.absoluteFilePath();
    }

    return a.exec();
}

Output:

Dir:  "C:/Qt"
Dir:  "C:/"
...
Dir:  "C:/Qt/build-QDir-Desktop_Qt_5_1_0_MSVC2012_OpenGL_64bit-Debug"
...
File:  "C:/Qt/FileA.txt"
File:  "C:/Qt/FileB.txt"
,,,
Dir:  "C:/Qt/test"