- Qt 5.15
- Qt D-Bus
- C++ Classes
- QDBusUnixFileDescriptor
- Qt 5.15.18 Reference Documentation

# QDBusUnixFileDescriptor Class

The QDBusUnixFileDescriptor class holds one Unix file descriptor. More...

Header: | #include <QDBusUnixFileDescriptor>
qmake: | QT += dbus
Since: | Qt 4.8

This class was introduced in Qt 4.8.

- List of all members, including inherited members

## Public Functions

| QDBusUnixFileDescriptor(const QDBusUnixFileDescriptor &other)
| QDBusUnixFileDescriptor(int fileDescriptor)
| QDBusUnixFileDescriptor()
QDBusUnixFileDescriptor & | operator=(const QDBusUnixFileDescriptor &other)
QDBusUnixFileDescriptor & | operator=(QDBusUnixFileDescriptor &&other)
| ~QDBusUnixFileDescriptor()
int | fileDescriptor() const
bool | isValid() const
void | setFileDescriptor(int fileDescriptor)
void | swap(QDBusUnixFileDescriptor &other)

## Static Public Members

bool | isSupported()

## Detailed Description

The QDBusUnixFileDescriptor class is used to hold one Unix file descriptor for use with the Qt D-Bus module. This allows applications to send and receive Unix file descriptors over the D-Bus connection, mapping automatically to the D-Bus type 'h'.

Objects of type QDBusUnixFileDescriptors can be used also as parameters in signals and slots that get exported to D-Bus by registering with QDBusConnection::registerObject.

QDBusUnixFileDescriptor does not take ownership of the file descriptor. Instead, it will use the Unix system call `dup(2)` to make a copy of the file descriptor. This file descriptor belongs to the QDBusUnixFileDescriptor object and should not be stored or closed by the user. Instead, you should make your own copy if you need that.

#### Availability

Unix file descriptor passing is not available in all D-Bus connections. This feature is present with D-Bus library and bus daemon version 1.4 and upwards on Unix systems. Qt D-Bus automatically enables the feature if such a version was found at compile-time and run-time.

To verify that your connection does support passing file descriptors, check if the QDBusConnection::UnixFileDescriptorPassing capability is set with QDBusConnection::connectionCapabilities(). If the flag is not active, then you will not be able to make calls to methods that have QDBusUnixFileDescriptor as arguments or even embed such a type in a variant. You will also not receive calls containing that type.

Note also that remote applications may not have support for Unix file descriptor passing. If you make a D-Bus to a remote application that cannot receive such a type, you will receive an error reply. If you try to send a signal containing a D-Bus file descriptor or return one from a method call, the message will be silently dropped.

Even if the feature is not available, QDBusUnixFileDescriptor will continue to operate, so code need not have compile-time checks for the availability of this feature.

On non-Unix systems, QDBusUnixFileDescriptor will always report an invalid state and QDBusUnixFileDescriptor::isSupported() will return false.

See also QDBusConnection::ConnectionCapabilities and QDBusConnection::connectionCapabilities().

## Member Function Documentation

### QDBusUnixFileDescriptor::QDBusUnixFileDescriptor(const QDBusUnixFileDescriptor &other)

Constructs a QDBusUnixFileDescriptor object by copying other.

### QDBusUnixFileDescriptor::QDBusUnixFileDescriptor(int fileDescriptor)

Constructs a QDBusUnixFileDescriptor object by copying the fileDescriptor parameter. The original file descriptor is not touched and must be closed by the user.

Note that the value returned by fileDescriptor() will be different from the fileDescriptor parameter passed.

If the fileDescriptor parameter is not valid, isValid() will return false and fileDescriptor() will return -1.

See also setFileDescriptor() and fileDescriptor().

### QDBusUnixFileDescriptor::QDBusUnixFileDescriptor()

Constructs a QDBusUnixFileDescriptor without a wrapped file descriptor. This is equivalent to constructing the object with an invalid file descriptor (like -1).

See also fileDescriptor() and isValid().

### QDBusUnixFileDescriptor &QDBusUnixFileDescriptor::operator=(const QDBusUnixFileDescriptor &other)

Copies the Unix file descriptor from the other QDBusUnixFileDescriptor object. If the current object contained a file descriptor, it will be properly disposed of before.

### QDBusUnixFileDescriptor &QDBusUnixFileDescriptor::operator=(QDBusUnixFileDescriptor &&other)

Move-assigns other to this QDBusUnixFileDescriptor.

### QDBusUnixFileDescriptor::~QDBusUnixFileDescriptor()

Destroys this QDBusUnixFileDescriptor object and disposes of the Unix file descriptor that it contained.

### int QDBusUnixFileDescriptor::fileDescriptor() const

Returns the Unix file descriptor contained by this QDBusUnixFileDescriptor object. An invalid file descriptor is represented by the value -1.

Note that the file descriptor returned by this function is owned by the QDBusUnixFileDescriptor object and must not be stored past the lifetime of this object. It is ok to use it while this object is valid, but if one wants to store it for longer use, the file descriptor should be cloned using the Unix `dup(2)`, `dup2(2)` or `dup3(2)` functions.

See also setFileDescriptor() and isValid().

### `[static]` bool QDBusUnixFileDescriptor::isSupported()

Returns `true` if Unix file descriptors are supported on this platform. In other words, this function returns `true` if this is a Unix platform.

Note that QDBusUnixFileDescriptor continues to operate even if this function returns `false`. The only difference is that the QDBusUnixFileDescriptor objects will always be in the isValid() == false state and fileDescriptor() will always return -1. The class will not consume any operating system resources.

### bool QDBusUnixFileDescriptor::isValid() const

Returns `true` if this Unix file descriptor is valid. A valid Unix file descriptor is not -1.

See also fileDescriptor().

### void QDBusUnixFileDescriptor::setFileDescriptor(int fileDescriptor)

Sets the file descriptor that this QDBusUnixFileDescriptor object holds to a copy of fileDescriptor. The original file descriptor is not touched and must be closed by the user.

Note that the value returned by fileDescriptor() will be different from the fileDescriptor parameter passed.

If the fileDescriptor parameter is not valid, isValid() will return false and fileDescriptor() will return -1.

See also isValid() and fileDescriptor().

### void QDBusUnixFileDescriptor::swap(QDBusUnixFileDescriptor &other)

Swaps this file descriptor instance with other. This function is very fast and never fails.

This function was introduced in Qt 5.0.