QDirListing Class

The QDirListing class provides an STL-style iterator for directory entries. More...

Header: #include <QDirListing>
CMake: find_package(Qt6 REQUIRED COMPONENTS Core)
target_link_libraries(mytarget PRIVATE Qt6::Core)
qmake: QT += core
Since: Qt 6.8

Public Types

class DirEntry
(since 6.8) class const_iterator
(since 6.8) class sentinel
enum class IteratorFlag { Default, ExcludeFiles, ExcludeDirs, ExcludeSpecial, ResolveSymlinks, …, FollowDirSymlinks }
flags IteratorFlags

Public Functions

QDirListing(const QString &path, QDirListing::IteratorFlags flags = IteratorFlag::Default)
QDirListing(const QString &path, const QStringList &nameFilters, QDirListing::IteratorFlags flags = IteratorFlag::Default)
QDirListing(QDirListing &&other)
~QDirListing()
QDirListing::const_iterator begin() const
QDirListing::const_iterator cbegin() const
QDirListing::sentinel cend() const
QDirListing::sentinel end() const
QDirListing::IteratorFlags iteratorFlags() const
QString iteratorPath() const
QStringList nameFilters() const
QDirListing &operator=(QDirListing &&other)

Detailed Description

You can use QDirListing to navigate entries of a directory one at a time. It is similar to QDir::entryList() and QDir::entryInfoList(), but because it lists entries one at a time instead of all at once, it scales better and is more suitable for large directories. It also supports listing directory contents recursively, and following symbolic links. Unlike QDir::entryList(), QDirListing does not support sorting.

The QDirListing constructor takes a directory path string as argument. Here's how to iterate over all entries recursively:

using ItFlag = QDirListing::IteratorFlag;
for (const auto &dirEntry : QDirListing(u"/etc"_s, ItFlag::Recursive)) {
    qDebug() << dirEntry.filePath();
    // /etc/.
    // /etc/..
    // /etc/X11
    // /etc/X11/fs
    // ...
}

Here's how to find and read all regular files filtered by name, recursively:

using F = QDirListing::IteratorFlag;
QDirListing dirList(u"/sys"_s, QStringList{u"scaling_cur_freq"_s}, F::FilesOnly | F::Recursive);
for (const auto &dirEntry : dirList) {
    QFile f(dirEntry.filePath());
    if (f.open(QIODevice::ReadOnly))
        qDebug() << f.fileName() << f.readAll().trimmed().toDouble() / 1000 << "MHz";
}

Here's how to list only regular files, recursively:

using F = QDirListing::IteratorFlag;
const auto flags = F::FilesOnly | F::Recursive;
for (const auto &dirEntry : QDirListing(u"/etc"_s, flags)) {
    // ...
}

Here's how to list only regular files and symbolic links to regular files, recursively:

using F = QDirListing::IteratorFlag;
const auto flags = F::FilesOnly | F::Recursive | F::ResolveSymlinks;
for (const auto &dirEntry : QDirListing(u"/etc"_s, flags)) {
    // ...
}

QDirListing::const_iterator models C++20 std::input_iterator, that is, it is a move-only, forward-only, single-pass iterator, that doesn't allow random access. It can be used in ranged-for loops (or with C++20 range algorithms that don't require random access iterators). Dereferencing a valid iterator returns a QDirListing::DirEntry object. The (c)end() sentinel marks the end of the iteration. Dereferencing an iterator that is equal to sentinel is undefined behavior.

QDirListing::DirEntry offers a subset of QFileInfo's API (for example, fileName(), filePath(), exists()). Internally, DirEntry only constructs a QFileInfo object if needed, that is, if the info hasn't been already fetched by other system functions. You can use DirEntry::fileInfo() to get a QFileInfo. For example:

using ItFlag = QDirListing::IteratorFlag;
for (const auto &dirEntry : QDirListing(u"/etc"_s, ItFlag::Recursive)) {
    // Faster
    if (dirEntry.fileName().endsWith(u".conf")) { /* ... */ }

    // This works, but might be potentially slower, since it has to construct a
    // QFileInfo, whereas (depending on the implementation) the fileName could
    // be known already
    if (dirEntry.fileInfo().fileName().endsWith(u".conf")) { /* ... */ }
}
using ItFlag = QDirListing::IteratorFlag;
for (const auto &dirEntry : QDirListing(u"/etc"_s, ItFlag::Recursive)) {
    // Both approaches are the same, because DirEntry will have to construct
    // a QFileInfo to get this info (for example, by calling system stat())

    if (dirEntry.size() >= 4'000 /* 4KB */) { /* ...*/ }
    if (dirEntry.fileInfo().size() >= 4'000 /* 4KB */) { /* ... */ }
}

See also QDir and QDir::entryList().

Member Type Documentation

enum class QDirListing::IteratorFlag
flags QDirListing::IteratorFlags

This enum class describes flags that can be used to configure the behavior of QDirListing. Values from this enumerator can be bitwise OR'ed together.

ConstantValueDescription
QDirListing::IteratorFlag::Default0x000000List all files, directories and symbolic links, including broken symlinks (where the target doesn't exist). Hidden files and directories and the special entries . and .. aren't listed by default.
QDirListing::IteratorFlag::ExcludeFiles0x000004Don't list regular files. When combined with ResolveSymlinks, symbolic links to regular files will be excluded too.
QDirListing::IteratorFlag::ExcludeDirs0x000008Don't list directories. When combined with ResolveSymlinks, symbolic links to directories will be excluded too.
QDirListing::IteratorFlag::ExcludeSpecial0x000010Don't list special system files:
  • On Unix: an entry that is not a directory, regular file or symbolic link (including broken symlinks). That is, FIFO, socket, character device, or block device.
  • On Windows: .lnk.
QDirListing::IteratorFlag::ResolveSymlinks0x000020Filter symbolic links based on the type of the target of the link, rather than the symbolic link itself. With this flag, broken symbolic links (where the target doesn't exist) are excluded. This flag is ignored on operating systems that don't support symbolic links.
QDirListing::IteratorFlag::FilesOnlyExcludeDirs | ExcludeSpecialOnly regular files will be listed. When combined with ResolveSymlinks, symbolic links to files will also be listed.
QDirListing::IteratorFlag::DirsOnlyExcludeFiles | ExcludeSpecialOnly directories will be listed. When combined with ResolveSymlinks, symbolic links to directories will also be listed.
QDirListing::IteratorFlag::IncludeHidden0x000040List hidden entries. When combined with Recursive, the iteration will recurse into hidden sub-directories as well.
QDirListing::IteratorFlag::IncludeDotAndDotDot0x000080List the . and .. special entries.
QDirListing::IteratorFlag::CaseSensitive0x000100The file glob patterns in the name filters passed to the QDirListing constructor, will be matched case sensitively (for details, see QDir::setNameFilters()).
QDirListing::IteratorFlag::Recursive0x000400List entries inside all sub-directories as well. When combined with FollowDirSymlinks, symbolic links to directories will be iterated too.
QDirListing::IteratorFlag::FollowDirSymlinks0x000800When combined with Recursive, symbolic links to directories will be iterated too. Symbolic link loops (e.g., link => . or link => ..) are automatically detected and ignored.

The IteratorFlags type is a typedef for QFlags<IteratorFlag>. It stores an OR combination of IteratorFlag values.

Member Function Documentation

QDirListing::const_iterator QDirListing::begin() const

QDirListing::const_iterator QDirListing::cbegin() const

QDirListing::sentinel QDirListing::cend() const

QDirListing::sentinel QDirListing::end() const

(c)begin() returns a QDirListing::const_iterator that can be used to iterate over directory entries.

  • This is a forward-only, single-pass iterator (you cannot iterate directory entries in reverse order)
  • Can't be copied, only std::move()d.
  • The return value of post-increment on objects that model std::input_iterator is partially-formed (a copy of an iterator that has since been advanced), the only valid operations on such an object are destruction and assignment of a new iterator. Therefore the post-increment operator advances the iterator and returns void.
  • Doesn't allow random access
  • Can be used in ranged-for loops; or with C++20 std::ranges algorithms that don't require random access iterators
  • Dereferencing a valid iterator returns a const DirEntry &
  • (c)end() returns a QDirListing::sentinel that signals the end of the iteration. Dereferencing an iterator that compares equal to end() is undefined behavior

Note: Each time (c)begin() is called on the same QDirListing object, the internal state is reset and the iteration starts anew.

(Some of the above restrictions are dictated by the underlying system library functions' implementation).

For example:

using ItFlag = QDirListing::IteratorFlag;
for (const auto &dirEntry : QDirListing(u"/etc"_s, ItFlag::Recursive)) {
    qDebug() << dirEntry.filePath();
    // /etc/.
    // /etc/..
    // /etc/X11
    // /etc/X11/fs
    // ...
}

Here's how to find and read all files filtered by name, recursively:

using F = QDirListing::IteratorFlag;
QDirListing dirList(u"/sys"_s, QStringList{u"scaling_cur_freq"_s}, F::FilesOnly | F::Recursive);
for (const auto &dirEntry : dirList) {
    QFile f(dirEntry.filePath());
    if (f.open(QIODevice::ReadOnly))
        qDebug() << f.fileName() << f.readAll().trimmed().toDouble() / 1000 << "MHz";
}

Note: The "classical" STL algorithms don't support iterator/sentinel, so you need to use C++20 std::ranges algorithms for QDirListing, or else a 3rd-party library that provides range-based algorithms in C++17.

See also QDirListing::DirEntry.

[explicit] QDirListing::QDirListing(const QString &path, QDirListing::IteratorFlags flags = IteratorFlag::Default)

Constructs a QDirListing that can iterate over path.

You can pass options via flags to control how the directory should be iterated.

By default, flags is IteratorFlag::Default.

See also IteratorFlags.

[explicit] QDirListing::QDirListing(const QString &path, const QStringList &nameFilters, QDirListing::IteratorFlags flags = IteratorFlag::Default)

Constructs a QDirListing that can iterate over path.

You can pass options via flags to control how the directory should be iterated. By default, flags is IteratorFlag::Default.

The listed entries will be filtered according to the file glob patterns in nameFilters (see QDir::setNameFilters() for more details).

For example, the following iterator could be used to iterate over audio files:

QDirListing audioFileIt(u"/home/johndoe/"_s, QStringList{u"*.mp3"_s, u"*.wav"_s},
                        QDirListing::IteratorFlag::FilesOnly);

See also IteratorFlags and QDir::setNameFilters().

[noexcept] QDirListing::QDirListing(QDirListing &&other)

Move constructor. Moves other into this QDirListing.

Note: The moved-from object other is placed in a partially-formed state, in which the only valid operations are destruction and assignment of a new value.

[noexcept] QDirListing::~QDirListing()

Destroys the QDirListing.

QDirListing::IteratorFlags QDirListing::iteratorFlags() const

Returns the set of IteratorFlags used to construct this QDirListing.

QString QDirListing::iteratorPath() const

Returns the directory path used to construct this QDirListing.

QStringList QDirListing::nameFilters() const

Returns the list of file name glob filters used to construct this QDirListing.

[noexcept] QDirListing &QDirListing::operator=(QDirListing &&other)

Move-assigns other to this QDirListing.

Note: The moved-from object other is placed in a partially-formed state, in which the only valid operations are destruction and assignment of a new value.

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