QFile Class

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

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

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

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

     QFile file("/proc/modules");
     if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
         return;

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

Member Function Documentation

QFile::QFile()

Constructs a QFile object.

[explicit] QFile::QFile(QObject *parent)

Constructs a new file object with the given parent.

QFile::QFile(const QString &name)

Constructs a new file object to represent the file with the given name.

[since 6.0] QFile::QFile(const std::filesystem::path &name)

Constructs a new file object to represent the file with the given name.

This function was introduced in Qt 6.0.

QFile::QFile(const QString &name, QObject *parent)

Constructs a new file object with the given parent to represent the file with the specified name.

[since 6.0] QFile::QFile(const std::filesystem::path &name, QObject *parent)

Constructs a new file object with the given parent to represent the file with the specified name.

This function was introduced in Qt 6.0.

[virtual noexcept] QFile::~QFile()

Destroys the file object, closing it if necessary.

bool QFile::copy(const QString &newName)

Copies the file named fileName() to newName.

This file is closed before it is copied.

If the copied file is a symbolic link (symlink), the file it refers to is copied, not the link itself. With the exception of permissions, which are copied, no other file metadata is copied.

Returns true if successful; otherwise returns false.

Note that if a file with the name newName already exists, copy() returns false. This means QFile will not overwrite it.

See also setFileName().

[since 6.0] bool QFile::copy(const std::filesystem::path &newName)

This is an overloaded function.

This function was introduced in Qt 6.0.

[static] bool QFile::copy(const QString &fileName, const QString &newName)

This is an overloaded function.

Copies the file named fileName to newName.

This file is closed before it is copied.

If the copied file is a symbolic link (symlink), the file it refers to is copied, not the link itself. With the exception of permissions, which are copied, no other file metadata is copied.

Returns true if successful; otherwise returns false.

Note that if a file with the name newName already exists, copy() returns false. This means QFile will not overwrite it.

See also rename().

[static] QString QFile::decodeName(const QByteArray &localFileName)

This does the reverse of QFile::encodeName() using localFileName.

See also encodeName().

[static] QString QFile::decodeName(const char *localFileName)

This is an overloaded function.

Returns the Unicode version of the given localFileName. See encodeName() for details.

[static] QByteArray QFile::encodeName(const QString &fileName)

Converts fileName to an 8-bit encoding that you can use in native APIs. On Windows, the encoding is the one from active Windows (ANSI) codepage. On other platforms, this is UTF-8, for macOS in decomposed form (NFD).

See also decodeName().

[static] bool QFile::exists(const QString &fileName)

Returns true if the file specified by fileName exists; otherwise returns false.

bool QFile::exists() const

This is an overloaded function.

Returns true if the file specified by fileName() exists; otherwise returns false.

See also fileName() and setFileName().

[override virtual] QString QFile::fileName() const

Reimplements: QFileDevice::fileName() const.

Returns the name set by setFileName() or to the QFile constructors.

See also setFileName() and QFileInfo::fileName().

[since 6.0] std::filesystem::path QFile::filesystemFileName() const

Returns fileName() as std::filesystem::path.

This function was introduced in Qt 6.0.

[since 6.3] std::filesystem::path QFile::filesystemSymLinkTarget() const

Returns symLinkTarget() as std::filesystem::path.

This function was introduced in Qt 6.3.

[static, since 6.3] std::filesystem::path QFile::filesystemSymLinkTarget(const std::filesystem::path &fileName)

Returns symLinkTarget() as std::filesystem::path of fileName.

This function was introduced in Qt 6.3.

bool QFile::link(const QString &linkName)

Creates a link named linkName that points to the file currently specified by fileName(). What a link is depends on the underlying filesystem (be it a shortcut on Windows or a symbolic link on Unix). Returns true if successful; otherwise returns false.

This function will not overwrite an already existing entity in the file system; in this case, link() will return false and set error() to return RenameError.

See also setFileName().

[since 6.0] bool QFile::link(const std::filesystem::path &newName)

This is an overloaded function.

This function was introduced in Qt 6.0.

[static] bool QFile::link(const QString &fileName, const QString &linkName)

This is an overloaded function.

Creates a link named linkName that points to the file fileName. What a link is depends on the underlying filesystem (be it a shortcut on Windows or a symbolic link on Unix). Returns true if successful; otherwise returns false.

See also link().

bool QFile::moveToTrash()

Moves the file specified by fileName() to the trash. Returns true if successful, and sets the fileName() to the path at which the file can be found within the trash; otherwise returns false.

The time for this function to run is independent of the size of the file being trashed. If this function is called on a directory, it may be proportional to the number of files being trashed. If the current fileName() points to a symbolic link, this function will move the link to the trash, possibly breaking it, not the target of the link.

This function uses the Windows and macOS APIs to perform the trashing on those two operating systems. Elsewhere (Unix systems), this function implements the FreeDesktop.org Trash specification version 1.0.

[static] bool QFile::moveToTrash(const QString &fileName, QString *pathInTrash = nullptr)

This is an overloaded function.

Moves the file specified by fileName to the trash. Returns true if successful, and sets pathInTrash (if provided) to the path at which the file can be found within the trash; otherwise returns false.

The time for this function to run is independent of the size of the file being trashed. If this function is called on a directory, it may be proportional to the number of files being trashed. If the current fileName() points to a symbolic link, this function will move the link to the trash, possibly breaking it, not the target of the link.

This function uses the Windows and macOS APIs to perform the trashing on those two operating systems. Elsewhere (Unix systems), this function implements the FreeDesktop.org Trash specification version 1.0.

[override virtual] bool QFile::open(QIODeviceBase::OpenMode mode)

Reimplements: QIODevice::open(QIODeviceBase::OpenMode mode).

Opens the file using OpenMode mode, returning true if successful; otherwise false.

The mode must be QIODevice::ReadOnly, QIODevice::WriteOnly, or QIODevice::ReadWrite. It may also have additional flags, such as QIODevice::Text and QIODevice::Unbuffered.

See also QT_USE_NODISCARD_FILE_OPEN, QIODevice::OpenMode, and setFileName().

[since 6.3] bool QFile::open(QIODeviceBase::OpenMode mode, QFileDevice::Permissions permissions)

This is an overloaded function.

If the file does not exist and mode implies creating it, it is created with the specified permissions.

On POSIX systems the actual permissions are influenced by the value of umask.

On Windows the permissions are emulated using ACLs. These ACLs may be in non-canonical order when the group is granted less permissions than others. Files and directories with such permissions will generate warnings when the Security tab of the Properties dialog is opened. Granting the group all permissions granted to others avoids such warnings.

This function was introduced in Qt 6.3.

See also QIODevice::OpenMode, setFileName(), and QT_USE_NODISCARD_FILE_OPEN.

bool QFile::open(FILE *fh, QIODeviceBase::OpenMode mode, QFileDevice::FileHandleFlags handleFlags = DontCloseHandle)

This is an overloaded function.

Opens the existing file handle fh in the given mode. handleFlags may be used to specify additional options. Returns true if successful; otherwise returns false.

Example:

 #include <stdio.h>

 void printError(const char* msg)
 {
     QFile file;
     file.open(stderr, QIODevice::WriteOnly);
     file.write(msg, qstrlen(msg));        // write to stderr
     file.close();
 }

When a QFile is opened using this function, behaviour of close() is controlled by the AutoCloseHandle flag. If AutoCloseHandle is specified, and this function succeeds, then calling close() closes the adopted handle. Otherwise, close() does not actually close the file, but only flushes it.

Warning:

1. If fh does not refer to a regular file, e.g., it is stdin, stdout, or stderr, you may not be able to seek(). size() returns 0 in those cases. See QIODevice::isSequential() for more information.
2. Since this function opens the file without specifying the file name, you cannot use this QFile with a QFileInfo.

Note for the Windows Platform

fh must be opened in binary mode (i.e., the mode string must contain 'b', as in "rb" or "wb") when accessing files and other random-access devices. Qt will translate the end-of-line characters if you pass QIODevice::Text to mode. Sequential devices, such as stdin and stdout, are unaffected by this limitation.

You need to enable support for console applications in order to use the stdin, stdout and stderr streams at the console. To do this, add the following declaration to your application's project file:

 CONFIG += console

See also close() and QT_USE_NODISCARD_FILE_OPEN.

bool QFile::open(int fd, QIODeviceBase::OpenMode mode, QFileDevice::FileHandleFlags handleFlags = DontCloseHandle)

This is an overloaded function.

Opens the existing file descriptor fd in the given mode. handleFlags may be used to specify additional options. Returns true if successful; otherwise returns false.

When a QFile is opened using this function, behaviour of close() is controlled by the AutoCloseHandle flag. If AutoCloseHandle is specified, and this function succeeds, then calling close() closes the adopted handle. Otherwise, close() does not actually close the file, but only flushes it.

See also close() and QT_USE_NODISCARD_FILE_OPEN.

[override virtual] QFileDevice::Permissions QFile::permissions() const

Reimplements: QFileDevice::permissions() const.

See also setPermissions().

[static] QFileDevice::Permissions QFile::permissions(const QString &fileName)

This is an overloaded function.

Returns the complete OR-ed together combination of QFile::Permission for fileName.

[static, since 6.0] QFileDevice::Permissions QFile::permissions(const std::filesystem::path &filename)

This is an overloaded function.

This function was introduced in Qt 6.0.

bool QFile::remove()

Removes the file specified by fileName(). Returns true if successful; otherwise returns false.

The file is closed before it is removed.

See also setFileName().

[static] bool QFile::remove(const QString &fileName)

This is an overloaded function.

Removes the file specified by the fileName given.

Returns true if successful; otherwise returns false.

See also remove().

bool QFile::rename(const QString &newName)

Renames the file currently specified by fileName() to newName. Returns true if successful; otherwise returns false.

If a file with the name newName already exists, rename() returns false (i.e., QFile will not overwrite it).

The file is closed before it is renamed.

If the rename operation fails, Qt will attempt to copy this file's contents to newName, and then remove this file, keeping only newName. If that copy operation fails or this file can't be removed, the destination file newName is removed to restore the old state.

See also setFileName().

[since 6.0] bool QFile::rename(const std::filesystem::path &newName)

This is an overloaded function.

This function was introduced in Qt 6.0.

[static] bool QFile::rename(const QString &oldName, const QString &newName)

This is an overloaded function.

Renames the file oldName to newName. Returns true if successful; otherwise returns false.

If a file with the name newName already exists, rename() returns false (i.e., QFile will not overwrite it).

See also rename().

[override virtual] bool QFile::resize(qint64 sz)

Reimplements: QFileDevice::resize(qint64 sz).

[static] bool QFile::resize(const QString &fileName, qint64 sz)

This is an overloaded function.

Sets fileName to size (in bytes) sz. Returns true if the resize succeeds; false otherwise. If sz is larger than fileName currently is the new bytes will be set to 0, if sz is smaller the file is simply truncated.

See also resize().

void QFile::setFileName(const QString &name)

Sets the name of the file. The name can have no path, a relative path, or an absolute path.

Do not call this function if the file has already been opened.

If the file name has no path or a relative path, the path used will be the application's current directory path at the time of the open() call.

Example:

 QFile file;
 QDir::setCurrent("/tmp");
 file.setFileName("readme.txt");
 QDir::setCurrent("/home");
 file.open(QIODevice::ReadOnly);      // opens "/home/readme.txt" under Unix

Note that the directory separator "/" works for all operating systems supported by Qt.

See also fileName(), QFileInfo, and QDir.

[since 6.0] void QFile::setFileName(const std::filesystem::path &name)

This is an overloaded function.

This function was introduced in Qt 6.0.

[override virtual] bool QFile::setPermissions(QFileDevice::Permissions permissions)

Reimplements: QFileDevice::setPermissions(QFileDevice::Permissions permissions).

Sets the permissions for the file to the permissions specified. Returns true if successful, or false if the permissions cannot be modified.

See also permissions() and setFileName().

[static] bool QFile::setPermissions(const QString &fileName, QFileDevice::Permissions permissions)

This is an overloaded function.

Sets the permissions for fileName file to permissions.

[static, since 6.0] bool QFile::setPermissions(const std::filesystem::path &filename, QFileDevice::Permissions permissionSpec)

This is an overloaded function.

This function was introduced in Qt 6.0.

[override virtual] qint64 QFile::size() const

Reimplements: QFileDevice::size() const.

[static] QString QFile::symLinkTarget(const QString &fileName)

Returns the absolute path of the file or directory referred to by the symlink (or shortcut on Windows) specified by fileName, or returns an empty string if the fileName does not correspond to a symbolic link.

This name may not represent an existing file; it is only a string. QFile::exists() returns true if the symlink points to an existing file.

QString QFile::symLinkTarget() const

This is an overloaded function.

Returns the absolute path of the file or directory a symlink (or shortcut on Windows) points to, or a an empty string if the object isn't a symbolic link.

This name may not represent an existing file; it is only a string. QFile::exists() returns true if the symlink points to an existing file.

See also fileName() and setFileName().