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QIODeviceBase Class

Base class for QIODevice that provides flags describing the mode in which a device is opened. More...

Header: #include <QIODevice>
CMake: find_package(Qt6 COMPONENTS Core REQUIRED) target_link_libraries(mytarget PRIVATE Qt6::Core)
qmake: QT += core
Inherited By:

QDataStream, QDebug, QIODevice, and QTextStream

Public Types

flags OpenMode
enum OpenModeFlag { NotOpen, ReadOnly, WriteOnly, ReadWrite, Append, …, ExistingOnly }

Detailed Description

Member Type Documentation

enum QIODeviceBase::OpenModeFlagflags QIODeviceBase::OpenMode

This enum is used with QIODevice::open() to describe the mode in which a device is opened. It is also returned by QIODevice::openMode().

Constant Value Description
QIODeviceBase::NotOpen 0x0000 The device is not open.
QIODeviceBase::ReadOnly 0x0001 The device is open for reading.
QIODeviceBase::WriteOnly 0x0002 The device is open for writing. Note that, for file-system subclasses (e.g. QFile), this mode implies Truncate unless combined with ReadOnly, Append or NewOnly.
QIODeviceBase::ReadWrite ReadOnly | WriteOnly The device is open for reading and writing.
QIODeviceBase::Append 0x0004 The device is opened in append mode so that all data is written to the end of the file.
QIODeviceBase::Truncate 0x0008 If possible, the device is truncated before it is opened. All earlier contents of the device are lost.
QIODeviceBase::Text 0x0010 When reading, the end-of-line terminators are translated to '\n'. When writing, the end-of-line terminators are translated to the local encoding, for example '\r\n' for Win32.
QIODeviceBase::Unbuffered 0x0020 Any buffer in the device is bypassed.
QIODeviceBase::NewOnly 0x0040 Fail if the file to be opened already exists. Create and open the file only if it does not exist. There is a guarantee from the operating system that you are the only one creating and opening the file. Note that this mode implies WriteOnly, and combining it with ReadWrite is allowed. This flag currently only affects QFile. Other classes might use this flag in the future, but until then using this flag with any classes other than QFile may result in undefined behavior. (since Qt 5.11)
QIODeviceBase::ExistingOnly 0x0080 Fail if the file to be opened does not exist. This flag must be specified alongside ReadOnly, WriteOnly, or ReadWrite. Note that using this flag with ReadOnly alone is redundant, as ReadOnly already fails when the file does not exist. This flag currently only affects QFile. Other classes might use this flag in the future, but until then using this flag with any classes other than QFile may result in undefined behavior. (since Qt 5.11)

Certain flags, such as Unbuffered and Truncate, are meaningless when used with some subclasses. Some of these restrictions are implied by the type of device that is represented by a subclass. In other cases, the restriction may be due to the implementation, or may be imposed by the underlying platform; for example, QTcpSocket does not support Unbuffered mode, and limitations in the native API prevent QFile from supporting Unbuffered on Windows.

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

© The Qt Company Ltd
Licensed under the GNU Free Documentation License, Version 1.3.
https://doc.qt.io/qt-6.2/qiodevicebase.html