How to read Linux key values, input subsystem, KEY,DEV/INPUT/EVENT,DEV/EVENT,C language keyboard

I believe you use embedded all want to read the key value directly, especially the chip manufacturers have provided input-driven cases, such as GPIO or scan the type of keyboard. So how do you get the key value in the application layer through the C language?

To the brothers a heavyweight source code, see below, we take to compile and run to know what is going on, of course, you can use Select instead of while () to read a little better, leaving you to imagine:

Attention:

#include <linux/input.h>

For the core source of the header file, note the path, generally for kernel/include/linux/input.h

EV.C:

* * Copyright 2002 Red Hat Inc., Durham, North Carolina.
 * All Rights Reserved. * * Permission is hereby granted, free of charge, to any person obtaining * a copy of this software and associated Docum Entation Files (The * "Software"), to deal in the Software without restriction, including * without limitation on the RI  Ghts to use, copy, modify, merge, * publish, distribute, sublicense, and/or sell copies of the Software, * and to permit Persons to whom the Software are furnished to does so, * subject to the following conditions: * * The above copyright not Ice and this permission notice (including the * next paragraph) shall is included in all copies or substantial * portion
 S of the Software. * * The SOFTWARE is provided ' as is ', without WARRANTY of any KIND, * EXPRESS OR implied, including BUT don't LIMITED to T  He warranties of the * merchantability, FITNESS for A particular purpose and * non-infringement. In NO EVENT SHALL RED HAT and/or their suppliers * is liable for Any CLAIM, damages or liability, WHETHER in a * ACTION of CONTRACT, TORT OR Otherwise, arising from, out of or in
 * CONNECTION with the SOFTWARE or, or other dealings, in the * SOFTWARE.
 * * This is the simple test program "reads from/dev/input/event*, * decoding events into a human readable form." * * * Authors: * Rickard E. (Rik) Faith <faith@redhat.com> * * */#include <stdio.h> #include <stdl ib.h> #include <unistd.h> #include <string.h> #include <sys/types.h> #include <fcntl.h> #

Include <errno.h> #include <time.h> #include <linux/input.h> struct input_event event;           int main (int argc, char **argv) {char name[64];  /* Rats:use OK, but could be better */char buf[256] = {0,}; /* rats:use OK */unsigned char MASK[EV_MAX/8 + 1];
    /* rats:use OK */int version;
    int fd = 0;
    int RC;
    int I, J; ChaR *tmp; #define TEST_BIT (bit) (mask[(bit)/8] & (1 << ((bit)%8)) for (i = 0; i < i++) {sprintf (name
        , "/dev/input/event%d", I);
            if (fd = open (name, o_rdonly, 0)) >= 0) {IOCTL (FD, eviocgversion, &version);
            IOCTL (FD, Eviocgname (sizeof (BUF)), buf);
            IOCTL (FD, eviocgbit (0, sizeof (mask)), mask);
            printf ("%s\n", name); printf ("Evdev version:%d.%d.%d\n", Version >>, (version >> 8) & 0xFF, Version & Amp
            0xFF);
            printf ("Name:%s\n", buf);
            printf ("Features:");
                    for (j = 0; J < Ev_max; J + +) {if (Test_bit (j)) {const char *type = "Unknown";
                    Switch (j) {Case ev_key:type = "keys/buttons";     Case ev_rel:type = "relative";
                    Break     Case ev_abs:type = "absolute";
    Break                Case ev_msc:type = "reserved";
                    Break         Case Ev_led:type = "LEDs";
                    Break        Case ev_snd:type = "sound";
                    Break       Case Ev_rep:type = "repeat";
                    Break     Case Ev_ff:type = "Feedback";
                    Break
                printf ("%s", type);
            printf ("\ n");
        Close (FD);
        } if (argc > 1) {sprintf (name, "/dev/input/event%d", Atoi (argv[1));
            if (fd = open (name, O_RDWR, 0) >= 0) {printf ("%s:open, FD =%d\n", name, FD);
                for (i = 0; i < Led_max. i++) {event.time.tv_sec = time (0);
                event.time.tv_usec = 0;
                Event.type = ev_led;
                Event.code = i;
                Event.value = 0;
            Write (fd, &event, sizeof (event));
            
 }           while (rc = Read (FD, &event, sizeof (event)) > 0) {printf ("%-24.24s.%0 6lu type 0x%04x; Code 0x%04x; "" Value 0x%08x;
                       ", CTime (&event.time.tv_sec), Event.time.tv_usec,
                Event.type, Event.code, Event.value);
                        Switch (event.type) {case ev_key:if (Event.code > Btn_misc) { printf ("button%d%s", Event.code & 0xFF, Event.val Ue?
                    "Press": "Release");
                               else {printf ("Key%d (0x%x)%s", Event.code & 0xFF, Event.code & 0xFF, Event.value?
                    "Press": "Release");
                } break;
 Case Ev_rel:switch (Event.code) {                   Case rel_x:tmp = "X";
                    Break       Case rel_y:tmp = "Y";
                    Break  Case rel_hwheel:tmp = "Hwheel";
                    Break    Case rel_dial:tmp = "DIAL";
                    Break   Case rel_wheel:tmp = "WHEEL";
                    Break    Case rel_misc:tmp = "MISC";
                    Break default:tmp = "UNKNOWN";
                    Break
                    printf ("Relative%s%d", TMP, Event.value);
                Break        Case Ev_abs:switch (event.code) {case abs_x:tmp = "X";
                    Break        Case abs_y:tmp = "Y";
                    Break        Case abs_z:tmp = "Z";
                    Break       Case abs_rx:tmp = "RX";
                    Break       Case abs_ry:tmp = "RY";
                    Break       Case abs_rz:tmp = "RZ";
      Break              Case abs_throttle:tmp = "throttle";
                    Break   Case abs_rudder:tmp = "rudder";
                    Break    Case abs_wheel:tmp = "WHEEL";
                    Break      Case abs_gas:tmp = "gas";
                    Break    Case abs_brake:tmp = "BRAKE";
                    Break    Case abs_hat0x:tmp = "hat0x";
                    Break    Case abs_hat0y:tmp = "hat0y";
                    Break    Case abs_hat1x:tmp = "hat1x";
                    Break    Case abs_hat1y:tmp = "hat1y";
                    Break    Case abs_hat2x:tmp = "hat2x";
                    Break    Case abs_hat2y:tmp = "hat2y";
                    Break    Case abs_hat3x:tmp = "hat3x";
                    Break    Case abs_hat3y:tmp = "hat3y";
                    Break Case abs_pressure:tmp = "pressure";
                    Break Case abs_distance:tmp = "DISTANCE";
                    Break Case abs_tilt_x:tmp = "Tilt_x ";
                    Break   Case abs_tilt_y:tmp = "tilt_y";
                    Break     Case abs_misc:tmp = "MISC";
                    Break  default:tmp = "UNKNOWN";
                    Break
                    printf ("Absolute%s%d", TMP, Event.value);
                Break Case ev_msc:printf ("Misc");
                Break  Case ev_led:printf ("LED");
                Break  Case ev_snd:printf ("SND");
                Break  Case ev_rep:printf ("REP");
                Break   Case ev_ff:printf ("FF");
                    Break
                Break
            printf ("\ n");
            printf ("rc =%d, (%s) \ n", RC, Strerror (errno));
        Close (FD);
} return 0; }