XLISTINPUTDEVICES - Online Linux Manual PageSection : 3
Updated : 09/15/2021
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NAMEXListInputDevices, XFreeDeviceList − list available input devices

SYNOPSIS#include <X11/extensions/XInput​.h>XDeviceInfo *XListInputDevices( Display *display, int *ndevices_return);int XFreeDeviceList( XDeviceInfo *list);display Specifies the connection to the X server​.ndevices_return Specifies a pointer to a variable where the number of available devices can be returned​.list Specifies the list of devices to free​. The XFreeDeviceList function frees the list of available extension input devices​.

DESCRIPTIONThe XListInputDevices request lists the available input devices​. This list includes the core keyboard and any physical input device currently accessible through the X server, and any input devices that are not currently accessible through the X server but could be accessed if requested​.A master pointer is a virtual pointer device that does not represent a physical device​. It is visually represented through a cursor​. A master keyboard is a virtual keyboard device that does not represent a physical device​. It is virtually represented through a keyboard focus​. A master pointer and a master keyboard are always paired (i​.e​. if shift is pressed on the master keyboard, a pointer click would be a shift−click)​. Multiple master pointer/keyboard pairs can exist​.X servers supporting the X Input Extension version 2, XListInputDevices only returns the first master pointer, the first master keyboard and all slave devices​. Additional master devices are not listed​.Physical devices (so−called slave devices) are attached to either a master pointer or a master keyboard, depending on their capabilities​. If a slave device generates an event, the event is also generated by the respective master device​. Multiple slave devices can be attached to a single master device​.Some server implementations may make all physical input devices available at the time the server is initialized​. Others may wait until requested by a client to access an input device​. In the latter case, it is possible that an input device will be listed as available at one time but not at another​.For each input device available to the server, the XListInputDevices request returns an XDeviceInfo structure​. That structure contains a pointer to a list of structures, each of which contains information about one class of input supported by the device​. The XDeviceInfo structure is defined as follows: typedef struct _XDeviceInfo { XID id; Atom type; char *name; int num_classes; int use; XAnyClassPtr inputclassinfo; } XDeviceInfo;The id is a number in the range 0−128 that uniquely identifies the device​. It is assigned to the device when it is initialized by the server​.The type field is of type Atom and indicates the nature of the device​. The type will correspond to one of the following strings (defined in the header file XI​.h):XI_MOUSE XI_TABLET XI_KEYBOARD XI_TOUCHSCREEN XI_TOUCHPAD XI_BUTTONBOX XI_BARCODE XI_TRACKBALL XI_QUADRATURE XI_ID_MODULE XI_ONE_KNOB XI_NINE_KNOB XI_KNOB_BOX XI_SPACEBALL XI_DATAGLOVE XI_EYETRACKER XI_CURSORKEYS XI_FOOTMOUSE XI_JOYSTICKThese strings may be used in an XInternAtom request to return an atom that can be compared with the type field of the XDeviceInfo structure​.The name field contains a pointer to a null−terminated string that serves as identifier of the device​. This identifier may be user−configured or automatically assigned by the server​.The num_classes field is a number in the range 0−255 that specifies the number of input classes supported by the device for which information is returned by ListInputDevices​. Some input classes, such as class Focus and class Proximity do not have any information to be returned by ListInputDevices​.All devices provide an AttachClass​. This class specifies the master device a given slave device is attached to​. For master devices, the class specifies the respective paired master device​.The use field specifies how the device is currently being used​. If the value is IsXKeyboard, the device is a master keyboard​. If the value is IsXPointer, the device is a master pointer​. If the value is IsXExtensionPointer, the device is a slave pointer​. If the value is IsXExtensionKeyboard, the device is a slave keyboard​. If the value is IsXExtensionDevice, the device is available for use as an extension device​.The inputclassinfo field contains a pointer to the first input−class specific data​. The first two fields are common to all classes​.The class field is a number in the range 0−255​. It uniquely identifies the class of input for which information is returned​. Currently defined classes are KeyClass, ButtonClass, and ValuatorClass​.The length field is a number in the range 0− 255​. It specifies the number of bytes of data that are contained in this input class​. The length includes the class and length fields​.The XKeyInfo structure describes the characteristics of the keys on the device​. It is defined as follows:typedef struct _XKeyInfo { XID class; int length; unsigned short min_keycode; unsigned short max_keycode; unsigned short num_keys; } XKeyInfo;min_keycode is of type KEYCODE​. It specifies the minimum keycode that the device will report​. The minimum keycode will not be smaller than 8​.max_keycode is of type KEYCODE​. It specifies the maximum keycode that the device will report​. The maximum keycode will not be larger than 255​.num_keys specifies the number of keys that the device has​.The XButtonInfo structure defines the characteristics of the buttons on the device​. It is defined as follows:typedef struct _XButtonInfo { XID class; int length; short num_buttons; } XButtonInfo;num_buttons specifies the number of buttons that the device has​.The XValuatorInfo structure defines the characteristics of the valuators on the device​. It is defined as follows:typedef struct _XValuatorInfo { XID class; int length; unsigned char num_axes; unsigned char mode; unsigned long motion_buffer; XAxisInfoPtr axes; } XValuatorInfo;num_axes contains the number of axes the device supports​.mode is a constant that has one of the following values: Absolute or Relative​. Some devices allow the mode to be changed dynamically via the SetDeviceMode request​.motion_buffer_size is a cardinal number that specifies the number of elements that can be contained in the motion history buffer for the device​.The axes field contains a pointer to an XAxisInfo structure​.The XAxisInfo structure is defined as follows:typedef struct _XAxisInfo { int resolution; int min_value; int max_value; } XAxisInfo;The resolution contains a number in counts/meter​.The min_val field contains a number that specifies the minimum value the device reports for this axis​. For devices whose mode is Relative, the min_val field will contain 0​.The max_val field contains a number that specifies the maximum value the device reports for this axis​. For devices whose mode is Relative, the max_val field will contain 0​.The XAttachInfo structure is defined as follows: typedef struct _XAttachInfo { int attached; } XAttachInfo;If the device is a slave device, attached specifies the device ID of the master device this device is attached to​. If the device is not attached to a master device, attached is Floating​. If the device is a master device, attached specifies the device ID of the master device this device is paired with​.

RETURN VALUEXListInputDevices returns a pointer to an array of XDeviceInfo structs and sets ndevices_return to the number of elements in that array​. To free the XDeviceInfo array created by XListInputDevices, use XFreeDeviceList​.On error, XListInputDevices returns NULL and ndevices_return is left unmodified​.
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