XIQueryDevice, XIFreeDeviceInfo − get information about devices.


#include <X11/extensions/XInput2.h>

XIDeviceInfo* XIQueryDevice( Display *display,
int deviceid,
int *ndevices_return);

XIFreeDeviceInfo( XIDeviceInfo *info);

Specifies the device to query or XIAllDevices or

Specifies the connection to the X server.

Returns the number of devices returned.

A list of device XIDeviceInfo structs to be freed.


The XIQueryDevice returns information about one or more input
devices. If the deviceid specifies a device, ndevices_return is
1 and the returned information describes only the requested
device. If deviceid is XIAllDevices or XIAllMasterDevices,
ndevices_return is the number of devices or master devices,
respectively, and the returned information represents all
devices or all master devices, respectively.

To free the XIDeviceInfo array returned by XIQueryDevice, use

For each input device requested, the XIQueryDevice returns an
XIDeviceInfo structure. Each structure contains information
about the capabilities of one input device available to the

typedef struct
int deviceid;
char *name;
int use;
int attachment;
Bool enabled;
int num_classes;
XIAnyClassInfo **classes;
} XIDeviceInfo;

The deviceid is the numeric unique id of the device. A deviceid
is unique for the life−time of a device but a server may re−use
the id once a device has been removed.

The name points to a null−terminated string specifying the
identifier of the device.

The use and attachment fields specify the type of the device
and the current attachment or pairing.
− If use is XIMasterPointer, the device is a master pointer and
attachment specifies the deviceid of the paired master
− If use is XIMasterKeyboard, the device is a master keyboard,
and the attachment field specifies the paired master pointer.
− If use is XISlavePointer, the device is a slave device and
currently attached to the master pointer specified in
− If use is XISlaveKeyboard, the device is a slave device an
currently attached to the master keyboard specified in
− If use is XIFloatingSlave, the device is a slave device
currently not attached to any master device. The value of the
attachment field for floating slave devices is undefined.

The enabled field specifies if the device is currently enabled
and can send events. Disabled devices will not send events.

The num_classes field specifies the number of input classes
pointed to by classes. The first two fields of all input
classes are identical.

typedef struct
int type;
int sourceid;
} XIAnyClassInfo;

The type field specifies the type of the input class.
Currently, the following types are defined:
XIKeyClass, XIButtonClass, XIValuatorClass

In the future, additional types may be added. Clients are
required to ignore unknown input classes.

The sourceid is the deviceid this class originated from. For
master devices, the sourceid is typically the id of the slave
device currently sending events. For slave devices, the
sourceid is typically the device´s id.

A device may have zero or one XIButtonClass, denoting the
device´s capability to send button events.

typedef struct {
int mask_len;
unsigned char *mask;
} XIButtonState;

typedef struct
int type;
int sourceid;
int num_buttons;
Atom *labels;
XIButtonState state;
} XIButtonClassInfo;

The num_buttons field specifies the number of buttons available
on this device. A device that has an XIButtonClass must have at
least one button.

labels is a list of num_buttons Atoms specifying the button
labels for this device. If the label is not None, then the
label specifies the type of button in physical device order
(i.e. as the buttons are numbered on the physical input

The state is the current button state as seen by clients (i.e.
after button mapping is applied). The mask_len field specifies
the length of mask in bytes. For each button on the device, the
respective bit in mask is set if the button is currently
logically down.

A device may have zero or one XIKeyClass, denoting the device´s
capability to send key events.

typedef struct
int type;
int sourceid;
int num_keycodes;
int *keycodes;
} XIKeyClassInfo;

The num_keycodes field specifies the number of keycodes
available on this device. A device that has an XIKeyClass must
have at least one keycode.

keycodes is a list of num_keycodes keycodes the device may

A device may have zero or more XIValuatorClass, denoting the
device´s capability to send coordinates.

typedef struct
int type;
int sourceid;
int number;
Atom label;
double min;
double max;
double value;
int resolution;
int mode;
} XIValuatorInfo;

The number field specifies the number of the axis on the
physical device.

If the label field is not None, the value of label is an Atom
describing the axis.

min and max are the minimum and maximum values allowed on this
axis. If both are zero, no minumum or maximum values are set on
this device. value is the current value of this axis.

The resolution field specifies the resolution of the device in

The mode specifies the mode of this axis. If the mode is
XIModeAbsolute this axis sends absolute coordinates. If the
mode is XIModeRelative, this device sends relative coordinates.

XIQueryDevice can generate a BadDevice error.

XIFreeDeviceInfo frees the information returned by


An invalid device was specified. The device does not
exist or is not a pointer device.


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