QFile Class | Qt Core | Qt 6.10.1
Description: The QFile class provides an interface for reading from and writing to files.

- Qt 6.10
- Qt Core
- C++ Classes
- QFile
- Qt 6.10.1 Reference Documentation

# QFile Class

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

Header: | `#include <QFile>`
CMake: | `find_package(Qt6 REQUIRED COMPONENTS Core)` `target_link_libraries(mytarget PRIVATE Qt6::Core)`
qmake: | `QT += core`
Inherits: | QFileDevice
Inherited By: | QTemporaryFile

- List of all members, including inherited members
- QFile is part of Input/Output and Networking.

Note: All functions in this class are reentrant.

## Public Functions

| QFile()
| QFile(QObject *parent)
| QFile(const QString &name)
`(since 6.0)` | QFile(const std::filesystem::path &name)
| QFile(const QString &name, QObject *parent)
`(since 6.0)` | QFile(const std::filesystem::path &name, QObject *parent)
virtual | ~QFile()
bool | copy(const QString &newName)
`(since 6.0)` bool | copy(const std::filesystem::path &newName)
bool | exists() const
`(since 6.0)` std::filesystem::path | filesystemFileName() const
`(since 6.3)` std::filesystem::path | filesystemSymLinkTarget() const
bool | link(const QString &linkName)
`(since 6.0)` bool | link(const std::filesystem::path &newName)
bool | moveToTrash()
`(since 6.3)` bool | open(QIODeviceBase::OpenMode mode, QFileDevice::Permissions permissions)
bool | open(FILE *fh, QIODeviceBase::OpenMode mode, QFileDevice::FileHandleFlags handleFlags = DontCloseHandle)
bool | open(int fd, QIODeviceBase::OpenMode mode, QFileDevice::FileHandleFlags handleFlags = DontCloseHandle)
bool | remove()
bool | rename(const QString &newName)
`(since 6.0)` bool | rename(const std::filesystem::path &newName)
void | setFileName(const QString &name)
`(since 6.0)` void | setFileName(const std::filesystem::path &name)
QString | symLinkTarget() const

## Reimplemented Public Functions

virtual QString | fileName() const override
virtual bool | open(QIODeviceBase::OpenMode mode) override
virtual QFileDevice::Permissions | permissions() const override
virtual bool | resize(qint64 sz) override
virtual bool | setPermissions(QFileDevice::Permissions permissions) override
virtual qint64 | size() const override

## Static Public Members

bool | copy(const QString &fileName, const QString &newName)
QString | decodeName(const QByteArray &localFileName)
QString | decodeName(const char *localFileName)
QByteArray | encodeName(const QString &fileName)
bool | exists(const QString &fileName)
`(since 6.3)` std::filesystem::path | filesystemSymLinkTarget(const std::filesystem::path &fileName)
bool | link(const QString &fileName, const QString &linkName)
bool | moveToTrash(const QString &fileName, QString *pathInTrash = nullptr)
QFileDevice::Permissions | permissions(const QString &fileName)
`(since 6.0)` QFileDevice::Permissions | permissions(const std::filesystem::path &filename)
bool | remove(const QString &fileName)
bool | rename(const QString &oldName, const QString &newName)
bool | resize(const QString &fileName, qint64 sz)
bool | setPermissions(const QString &fileName, QFileDevice::Permissions permissions)
`(since 6.0)` bool | setPermissions(const std::filesystem::path &filename, QFileDevice::Permissions permissionSpec)
`(since 6.9)` bool | supportsMoveToTrash()
QString | symLinkTarget(const QString &fileName)

## Detailed Description

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.

You can check for a file's existence using exists(), and remove a file using remove(). (More advanced file system related operations are provided by QFileInfo and QDir.)

The file is opened with open(), closed with close(), and flushed with flush(). Data is usually read and written using QDataStream or QTextStream, but you can also call the QIODevice-inherited functions read(), readLine(), readAll(), write(). QFile also inherits getChar(), putChar(), and ungetChar(), which work one character at a time.

The size of the file is returned by size(). You can get the current file position using pos(), or move to a new file position using seek(). If you've reached the end of the file, atEnd() returns `true`.

### 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 Text flag passed to open() tells Qt to convert Windows-style line terminators ("\r\n") 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.

### 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 file is encoded in UTF-8. This can be changed using QTextStream::setEncoding().

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";

QDataStream is similar, in that you can use operator<<() to write data and operator>>() to read it back. See the class documentation for details.

### Signals

Unlike other QIODevice implementations, such as QTcpSocket, QFile does not emit the aboutToClose(), bytesWritten(), or readyRead() signals. This implementation detail means that QFile is not suitable for reading and writing certain types of files, such as device files on Unix platforms.

### Platform Specific Issues

Qt APIs related to I/O use UTF-16 based QStrings to represent file paths. Standard C++ APIs (`<cstdio>` or `<iostream>`) or platform-specific APIs however often need a 8-bit encoded path. You can use encodeName() and decodeName() to convert between both representations.

On Unix, there are some special system files (e.g. in `/proc`) for which size() will always return 0, yet you may still be able to read more data from such a file; the data is generated in direct response to you calling read(). In this case, however, you cannot use atEnd() to determine if there is more data to read (since atEnd() will return true for a file that claims to have size 0). Instead, you should either call readAll(), or call read() or readLine() repeatedly until no more data can be read. The next example uses QTextStream to read `/proc/modules` line by line:

         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();
         }

File permissions are handled differently on Unix-like systems and Windows. In a non writable directory on Unix-like systems, files cannot be created. This is not always the case on Windows, where, for instance, the 'My Documents' directory usually is not writable, but it is still possible to create files in it.

Qt's understanding of file permissions is limited, which affects especially the QFile::setPermissions() function. On Windows, Qt will set only the legacy read-only flag, and that only when none of the Write* flags are passed. Qt does not manipulate access control lists (ACLs), which makes this function mostly useless for NTFS volumes. It may still be of use for USB sticks that use VFAT file systems. POSIX ACLs are not manipulated, either.

On Android, some limitations apply when dealing with content URIs:

- Access permissions might be needed by prompting the user through the QFileDialog which implements Android's native file picker.
- Aim to follow the Scoped storage guidelines, such as using app specific directories instead of other public external directories. For more information, also see storage best practices.
- Due to the design of Qt APIs (e.g. QFile), it's not possible to fully integrate the latter APIs with Android's MediaStore APIs.

See also QTextStream, QDataStream, QFileInfo, QDir, and The Qt Resource System.

## Member Function Documentation

### QFile::QFile()

Constructs a QFile object.

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

Constructs a new file object with the given parent.

### `[explicit]` QFile::QFile(const QString &name)

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

Note: In versions up to and including Qt 6.8, this constructor is implicit, for backward compatibility. Starting from Qt 6.9 this constructor is unconditionally `explicit`. Users can force this constructor to be `explicit` even in earlier versions of Qt by defining the `QT_EXPLICIT_QFILE_CONSTRUCTION_FROM_PATH` macro before including any Qt header.

### `[explicit, since 6.0]` QFile::QFile(const std::filesystem::path &name)

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

Note: In versions up to and including Qt 6.8, this constructor is implicit, for backward compatibility. Starting from Qt 6.9 this constructor is unconditionally `explicit`. Users can force this constructor to be `explicit` even in earlier versions of Qt by defining the `QT_EXPLICIT_QFILE_CONSTRUCTION_FROM_PATH` macro before including any Qt header.

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.

Note: On Android, this operation is not yet supported for `content` scheme URIs.

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)

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.

Note: On Android, this operation is not yet supported for `content` scheme URIs.

This is an overloaded function.

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)

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

This is an overloaded function.

### `[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`.

Note: If fileName is a symlink that points to a non-existing file, false is returned.

### bool QFile::exists() const

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

This is an overloaded function.

See also fileName() and setFileName().

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

Reimplements: QFileDevice::fileName() const.

Returns the name of the file as set by setFileName(), rename(), or by the QFile constructors.

See also setFileName(), rename(), 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.

Note: To create a valid link on Windows, linkName must have a `.lnk` file extension.

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)

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`.

This is an overloaded function.

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.

Note: When using the FreeDesktop.org Trash implementation, this function will fail if it is unable to move the files to the trash location by way of file renames and hardlinks. This condition arises if the file being trashed resides on a volume (mount point) on which the current user does not have permission to create the `.Trash` directory, or with some unusual filesystem types or configurations (such as sub-volumes that aren't themselves mount points).

Note: On systems where the system API doesn't report the location of the file in the trash, fileName() will be set to the null string once the file has been moved. On systems that don't have a trash can, this function always returns `false` (see supportsMoveToTrash()).

See also supportsMoveToTrash(), remove(), and QDir::remove().

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

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.

Note: When using the FreeDesktop.org Trash implementation, this function will fail if it is unable to move the files to the trash location by way of file renames and hardlinks. This condition arises if the file being trashed resides on a volume (mount point) on which the current user does not have permission to create the `.Trash` directory, or with some unusual filesystem types or configurations (such as sub-volumes that aren't themselves mount points).

Note: On systems where the system API doesn't report the path of the file in the trash, pathInTrash will be set to the null string once the file has been moved. On systems that don't have a trash can, this function always returns false.

This is an overloaded function.

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

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

Opens the file using mode flags, returning `true` if successful; otherwise returns `false`.

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

Note: In WriteOnly or ReadWrite mode, if the relevant file does not already exist, this function will try to create a new file before opening it. The file will be created with mode 0666 masked by the umask on POSIX systems, and with permissions inherited from the parent directory on Windows. On Android, it's expected to have access permission to the parent of the file name, otherwise, it won't be possible to create this non-existing file.

See also QT_USE_NODISCARD_FILE_OPEN and setFileName().

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

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 is an overloaded function.

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)

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

This is an overloaded function.

See also close() and QT_USE_NODISCARD_FILE_OPEN.

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

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.

Warning: If fd is not a regular file, e.g, it is 0 (`stdin`), 1 (`stdout`), or 2 (`stderr`), you may not be able to seek(). In those cases, size() returns `0`. See QIODevice::isSequential() for more information.

Warning: Since this function opens the file without specifying the file name, you cannot use this QFile with a QFileInfo.

This is an overloaded function.

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)

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

This is an overloaded function.

### `[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)

Removes the file specified by the fileName given.

Returns `true` if successful; otherwise returns `false`.

This is an overloaded function.

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)

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).

This is an overloaded function.

See also rename().

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

Reimplements: QFileDevice::resize(qint64 sz).

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

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.

Warning: This function can fail if the file doesn't exist.

This is an overloaded function.

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.

Warning: This function does not manipulate ACLs, which may limit its effectiveness.

See also permissions() and setFileName().

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

Sets the permissions for fileName file to permissions.

This is an overloaded function.

### `[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, since 6.9]` bool QFile::supportsMoveToTrash()

Returns `true` if Qt supports moving files to a trash (recycle bin) in the current operating system using the moveToTrash() function, `false` otherwise. Note that this function returning `true` does not imply moveToTrash() will succeed. In particular, this function does not check if the user has disabled the functionality in their settings.

This function was introduced in Qt 6.9.

See also moveToTrash().

### `[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

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.

This is an overloaded function.

See also fileName() and setFileName().