Listing Available Input Devices

To obtain a list of available input devices, use XHPListInputDevices.

XHPDeviceList *XHPListInputDevices(display, ndevices)
      Display *display;
      int     *ndevices;                /* RETURN */

XHPListInputDevices returns information about the input devices that are available to the X server, including the standard X keyboard and pointer devices. Each time it is called it returns a pointer to an array of XHPDeviceList structures that contains information about each device. The ndevices value returned specifies the number of XHPDeviceList structures in the array. In < X11/XHPlib.h >, the XHPDeviceList structure is defined as follows:

typedef struct                         

    {                                  

    unsigned int      resolution;  
/* resolution in counts/meter */

    unsigned short    min_val;     
/* min value this axis returns*/

    unsigned short    max_val;     
/* max value this axis returns*/

    } XHPaxis_info;                    

typedef struct                         

    {                                  

    XID               x_id;        
/* device X identifier        */

    char              *name;       
/* device name                */

    XHPaxis_info      *axes;       
/* pointer to axes array      */

    unsigned short    type;        
/* device type                */

    unsigned short    min_keycode; 
/* min X keycode from this dev*/

    unsigned short    max_keycode; 
/* max X keycode from this dev*/

    unsigned char     hil_id;      
/* device HIL identifier      */

    unsigned char     mode;        
/* ABSOLUTE or RELATIVE       */

    unsigned char     num_axes;    
/* # axes this device has     */

    unsigned char     num_buttons; 
/* # buttons on this device   */

    unsigned char     num_keys;    
/* # keys on this device      */

    unsigned char     io_byte;     
/* I/O descriptor byte for dev*/

    unsigned short    detailed_id; 
/* kbd interface + type       */

    unsigned char     pad[6];      
/* reserved for future use    */

    } XHPDeviceList;                   

The axes field of the HPDeviceList structure contains the address of an array of XHPaxis_info structures. The num_axes field contains the number of elements in this array. If the num_axes field contains 0 (zero), the contents of the axes field will be NULL. In the XHPaxis_info structure the resolution field contains the resolution of the device in counts per meter. If the mode field of the XHPDeviceList structure is ABSOLUTE, then the min_val and max_val fields contain the minimum and maximum values the device can report. For relative pointing devices, these fields contain 0 (zero).

The X pointer device is always the first device listed and has an x_id field equal to the constant XPOINTER. The X keyboard device is always listed second and has an x_id field equal to the constant XKEYBOARD. In general, attempting to access the X keyboard or pointer devices using the HP extension functions generates a BadDevice error.

A variety of device types are defined in < X11/XHPlib.h >.

XHPDeviceList returns NULL if there are no input devices to list.