奇怪的数组初始化(从C移植到C ++)

时间:2017-01-20 16:36:56

标签: c++ c arrays initialization porting

我正在尝试将一个名为“evtest”的小应用程序从C语言移植到C ++,并且在我以前从未见过的以下数组初始化(这看起来与g ++不兼容)上进行了简化:

char *events[EV_MAX + 1] = {
    [0 ... EV_MAX] = NULL,
    [EV_SYN] = "Sync",          [EV_KEY] = "Key",
    [EV_REL] = "Relative",          [EV_ABS] = "Absolute",
    [EV_MSC] = "Misc",          [EV_LED] = "LED",
    [EV_SND] = "Sound",         [EV_REP] = "Repeat",
    [EV_FF] = "ForceFeedback",      [EV_PWR] = "Power",
    [EV_FF_STATUS] = "ForceFeedbackStatus",
};

以下是完整代码:

//evtest.c
#include <stdint.h>

#include <linux/input.h>

#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>

#ifndef EV_SYN
#define EV_SYN 0
#endif

char *events[EV_MAX + 1] = {
    [0 ... EV_MAX] = NULL,
    [EV_SYN] = "Sync",          [EV_KEY] = "Key",
    [EV_REL] = "Relative",          [EV_ABS] = "Absolute",
    [EV_MSC] = "Misc",          [EV_LED] = "LED",
    [EV_SND] = "Sound",         [EV_REP] = "Repeat",
    [EV_FF] = "ForceFeedback",      [EV_PWR] = "Power",
    [EV_FF_STATUS] = "ForceFeedbackStatus",
};

char *keys[KEY_MAX + 1] = {
    [0 ... KEY_MAX] = NULL,
    [KEY_RESERVED] = "Reserved",        [KEY_ESC] = "Esc",
    [KEY_1] = "1",              [KEY_2] = "2",
    [KEY_3] = "3",              [KEY_4] = "4",
    [KEY_5] = "5",              [KEY_6] = "6",
    [KEY_7] = "7",              [KEY_8] = "8",
    [KEY_9] = "9",              [KEY_0] = "0",
    [KEY_MINUS] = "Minus",          [KEY_EQUAL] = "Equal",
    [KEY_BACKSPACE] = "Backspace",      [KEY_TAB] = "Tab",
    [KEY_Q] = "Q",              [KEY_W] = "W",
    [KEY_E] = "E",              [KEY_R] = "R",
    [KEY_T] = "T",              [KEY_Y] = "Y",
    [KEY_U] = "U",              [KEY_I] = "I",
    [KEY_O] = "O",              [KEY_P] = "P",
    [KEY_LEFTBRACE] = "LeftBrace",      [KEY_RIGHTBRACE] = "RightBrace",
    [KEY_ENTER] = "Enter",          [KEY_LEFTCTRL] = "LeftControl",
    [KEY_A] = "A",              [KEY_S] = "S",
    [KEY_D] = "D",              [KEY_F] = "F",
    [KEY_G] = "G",              [KEY_H] = "H",
    [KEY_J] = "J",              [KEY_K] = "K",
    [KEY_L] = "L",              [KEY_SEMICOLON] = "Semicolon",
    [KEY_APOSTROPHE] = "Apostrophe",    [KEY_GRAVE] = "Grave",
    [KEY_LEFTSHIFT] = "LeftShift",      [KEY_BACKSLASH] = "BackSlash",
    [KEY_Z] = "Z",              [KEY_X] = "X",
    [KEY_C] = "C",              [KEY_V] = "V",
    [KEY_B] = "B",              [KEY_N] = "N",
    [KEY_M] = "M",              [KEY_COMMA] = "Comma",
    [KEY_DOT] = "Dot",          [KEY_SLASH] = "Slash",
    [KEY_RIGHTSHIFT] = "RightShift",    [KEY_KPASTERISK] = "KPAsterisk",
    [KEY_LEFTALT] = "LeftAlt",      [KEY_SPACE] = "Space",
    [KEY_CAPSLOCK] = "CapsLock",        [KEY_F1] = "F1",
    [KEY_F2] = "F2",            [KEY_F3] = "F3",
    [KEY_F4] = "F4",            [KEY_F5] = "F5",
    [KEY_F6] = "F6",            [KEY_F7] = "F7",
    [KEY_F8] = "F8",            [KEY_F9] = "F9",
    [KEY_F10] = "F10",          [KEY_NUMLOCK] = "NumLock",
    [KEY_SCROLLLOCK] = "ScrollLock",    [KEY_KP7] = "KP7",
    [KEY_KP8] = "KP8",          [KEY_KP9] = "KP9",
    [KEY_KPMINUS] = "KPMinus",      [KEY_KP4] = "KP4",
    [KEY_KP5] = "KP5",          [KEY_KP6] = "KP6",
    [KEY_KPPLUS] = "KPPlus",        [KEY_KP1] = "KP1",
    [KEY_KP2] = "KP2",          [KEY_KP3] = "KP3",
    [KEY_KP0] = "KP0",          [KEY_KPDOT] = "KPDot",
    [KEY_ZENKAKUHANKAKU] = "Zenkaku/Hankaku", [KEY_102ND] = "102nd",
    [KEY_F11] = "F11",          [KEY_F12] = "F12",
    [KEY_RO] = "RO",            [KEY_KATAKANA] = "Katakana",
    [KEY_HIRAGANA] = "HIRAGANA",        [KEY_HENKAN] = "Henkan",
    [KEY_KATAKANAHIRAGANA] = "Katakana/Hiragana", [KEY_MUHENKAN] = "Muhenkan",
    [KEY_KPJPCOMMA] = "KPJpComma",      [KEY_KPENTER] = "KPEnter",
    [KEY_RIGHTCTRL] = "RightCtrl",      [KEY_KPSLASH] = "KPSlash",
    [KEY_SYSRQ] = "SysRq",          [KEY_RIGHTALT] = "RightAlt",
    [KEY_LINEFEED] = "LineFeed",        [KEY_HOME] = "Home",
    [KEY_UP] = "Up",            [KEY_PAGEUP] = "PageUp",
    [KEY_LEFT] = "Left",            [KEY_RIGHT] = "Right",
    [KEY_END] = "End",          [KEY_DOWN] = "Down",
    [KEY_PAGEDOWN] = "PageDown",        [KEY_INSERT] = "Insert",
    [KEY_DELETE] = "Delete",        [KEY_MACRO] = "Macro",
    [KEY_MUTE] = "Mute",            [KEY_VOLUMEDOWN] = "VolumeDown",
    [KEY_VOLUMEUP] = "VolumeUp",        [KEY_POWER] = "Power",
    [KEY_KPEQUAL] = "KPEqual",      [KEY_KPPLUSMINUS] = "KPPlusMinus",
    [KEY_PAUSE] = "Pause",          [KEY_KPCOMMA] = "KPComma",
    [KEY_HANGUEL] = "Hanguel",      [KEY_HANJA] = "Hanja",
    [KEY_YEN] = "Yen",          [KEY_LEFTMETA] = "LeftMeta",
    [KEY_RIGHTMETA] = "RightMeta",      [KEY_COMPOSE] = "Compose",
    [KEY_STOP] = "Stop",            [KEY_AGAIN] = "Again",
    [KEY_PROPS] = "Props",          [KEY_UNDO] = "Undo",
    [KEY_FRONT] = "Front",          [KEY_COPY] = "Copy",
    [KEY_OPEN] = "Open",            [KEY_PASTE] = "Paste",
    [KEY_FIND] = "Find",            [KEY_CUT] = "Cut",
    [KEY_HELP] = "Help",            [KEY_MENU] = "Menu",
    [KEY_CALC] = "Calc",            [KEY_SETUP] = "Setup",
    [KEY_SLEEP] = "Sleep",          [KEY_WAKEUP] = "WakeUp",
    [KEY_FILE] = "File",            [KEY_SENDFILE] = "SendFile",
    [KEY_DELETEFILE] = "DeleteFile",    [KEY_XFER] = "X-fer",
    [KEY_PROG1] = "Prog1",          [KEY_PROG2] = "Prog2",
    [KEY_WWW] = "WWW",          [KEY_MSDOS] = "MSDOS",
    [KEY_COFFEE] = "Coffee",        [KEY_DIRECTION] = "Direction",
    [KEY_CYCLEWINDOWS] = "CycleWindows",    [KEY_MAIL] = "Mail",
    [KEY_BOOKMARKS] = "Bookmarks",      [KEY_COMPUTER] = "Computer",
    [KEY_BACK] = "Back",            [KEY_FORWARD] = "Forward",
    [KEY_CLOSECD] = "CloseCD",      [KEY_EJECTCD] = "EjectCD",
    [KEY_EJECTCLOSECD] = "EjectCloseCD",    [KEY_NEXTSONG] = "NextSong",
    [KEY_PLAYPAUSE] = "PlayPause",      [KEY_PREVIOUSSONG] = "PreviousSong",
    [KEY_STOPCD] = "StopCD",        [KEY_RECORD] = "Record",
    [KEY_REWIND] = "Rewind",        [KEY_PHONE] = "Phone",
    [KEY_ISO] = "ISOKey",           [KEY_CONFIG] = "Config",
    [KEY_HOMEPAGE] = "HomePage",        [KEY_REFRESH] = "Refresh",
    [KEY_EXIT] = "Exit",            [KEY_MOVE] = "Move",
    [KEY_EDIT] = "Edit",            [KEY_SCROLLUP] = "ScrollUp",
    [KEY_SCROLLDOWN] = "ScrollDown",    [KEY_KPLEFTPAREN] = "KPLeftParenthesis",
    [KEY_KPRIGHTPAREN] = "KPRightParenthesis", [KEY_F13] = "F13",
    [KEY_F14] = "F14",          [KEY_F15] = "F15",
    [KEY_F16] = "F16",          [KEY_F17] = "F17",
    [KEY_F18] = "F18",          [KEY_F19] = "F19",
    [KEY_F20] = "F20",          [KEY_F21] = "F21",
    [KEY_F22] = "F22",          [KEY_F23] = "F23",
    [KEY_F24] = "F24",          [KEY_PLAYCD] = "PlayCD",
    [KEY_PAUSECD] = "PauseCD",      [KEY_PROG3] = "Prog3",
    [KEY_PROG4] = "Prog4",          [KEY_SUSPEND] = "Suspend",
    [KEY_CLOSE] = "Close",          [KEY_PLAY] = "Play",
    [KEY_FASTFORWARD] = "Fast Forward", [KEY_BASSBOOST] = "Bass Boost",
    [KEY_PRINT] = "Print",          [KEY_HP] = "HP",
    [KEY_CAMERA] = "Camera",        [KEY_SOUND] = "Sound",
    [KEY_QUESTION] = "Question",        [KEY_EMAIL] = "Email",
    [KEY_CHAT] = "Chat",            [KEY_SEARCH] = "Search",
    [KEY_CONNECT] = "Connect",      [KEY_FINANCE] = "Finance",
    [KEY_SPORT] = "Sport",          [KEY_SHOP] = "Shop",
    [KEY_ALTERASE] = "Alternate Erase", [KEY_CANCEL] = "Cancel",
    [KEY_BRIGHTNESSDOWN] = "Brightness down", [KEY_BRIGHTNESSUP] = "Brightness up",
    [KEY_MEDIA] = "Media",          [KEY_UNKNOWN] = "Unknown",
    [BTN_0] = "Btn0",           [BTN_1] = "Btn1",
    [BTN_2] = "Btn2",           [BTN_3] = "Btn3",
    [BTN_4] = "Btn4",           [BTN_5] = "Btn5",
    [BTN_6] = "Btn6",           [BTN_7] = "Btn7",
    [BTN_8] = "Btn8",           [BTN_9] = "Btn9",
    [BTN_LEFT] = "LeftBtn",         [BTN_RIGHT] = "RightBtn",
    [BTN_MIDDLE] = "MiddleBtn",     [BTN_SIDE] = "SideBtn",
    [BTN_EXTRA] = "ExtraBtn",       [BTN_FORWARD] = "ForwardBtn",
    [BTN_BACK] = "BackBtn",         [BTN_TASK] = "TaskBtn",
    [BTN_TRIGGER] = "Trigger",      [BTN_THUMB] = "ThumbBtn",
    [BTN_THUMB2] = "ThumbBtn2",     [BTN_TOP] = "TopBtn",
    [BTN_TOP2] = "TopBtn2",         [BTN_PINKIE] = "PinkieBtn",
    [BTN_BASE] = "BaseBtn",         [BTN_BASE2] = "BaseBtn2",
    [BTN_BASE3] = "BaseBtn3",       [BTN_BASE4] = "BaseBtn4",
    [BTN_BASE5] = "BaseBtn5",       [BTN_BASE6] = "BaseBtn6",
    [BTN_DEAD] = "BtnDead",         [BTN_A] = "BtnA",
    [BTN_B] = "BtnB",           [BTN_C] = "BtnC",
    [BTN_X] = "BtnX",           [BTN_Y] = "BtnY",
    [BTN_Z] = "BtnZ",           [BTN_TL] = "BtnTL",
    [BTN_TR] = "BtnTR",         [BTN_TL2] = "BtnTL2",
    [BTN_TR2] = "BtnTR2",           [BTN_SELECT] = "BtnSelect",
    [BTN_START] = "BtnStart",       [BTN_MODE] = "BtnMode",
    [BTN_THUMBL] = "BtnThumbL",     [BTN_THUMBR] = "BtnThumbR",
    [BTN_TOOL_PEN] = "ToolPen",     [BTN_TOOL_RUBBER] = "ToolRubber",
    [BTN_TOOL_BRUSH] = "ToolBrush",     [BTN_TOOL_PENCIL] = "ToolPencil",
    [BTN_TOOL_AIRBRUSH] = "ToolAirbrush",   [BTN_TOOL_FINGER] = "ToolFinger",
    [BTN_TOOL_MOUSE] = "ToolMouse",     [BTN_TOOL_LENS] = "ToolLens",
    [BTN_TOUCH] = "Touch",          [BTN_STYLUS] = "Stylus",
    [BTN_STYLUS2] = "Stylus2",      [BTN_TOOL_DOUBLETAP] = "Tool Doubletap",
    [BTN_TOOL_TRIPLETAP] = "Tool Tripletap", [BTN_GEAR_DOWN] = "WheelBtn",
    [BTN_GEAR_UP] = "Gear up",      [KEY_OK] = "Ok",
    [KEY_SELECT] = "Select",        [KEY_GOTO] = "Goto",
    [KEY_CLEAR] = "Clear",          [KEY_POWER2] = "Power2",
    [KEY_OPTION] = "Option",        [KEY_INFO] = "Info",
    [KEY_TIME] = "Time",            [KEY_VENDOR] = "Vendor",
    [KEY_ARCHIVE] = "Archive",      [KEY_PROGRAM] = "Program",
    [KEY_CHANNEL] = "Channel",      [KEY_FAVORITES] = "Favorites",
    [KEY_EPG] = "EPG",          [KEY_PVR] = "PVR",
    [KEY_MHP] = "MHP",          [KEY_LANGUAGE] = "Language",
    [KEY_TITLE] = "Title",          [KEY_SUBTITLE] = "Subtitle",
    [KEY_ANGLE] = "Angle",          [KEY_ZOOM] = "Zoom",
    [KEY_MODE] = "Mode",            [KEY_KEYBOARD] = "Keyboard",
    [KEY_SCREEN] = "Screen",        [KEY_PC] = "PC",
    [KEY_TV] = "TV",            [KEY_TV2] = "TV2",
    [KEY_VCR] = "VCR",          [KEY_VCR2] = "VCR2",
    [KEY_SAT] = "Sat",          [KEY_SAT2] = "Sat2",
    [KEY_CD] = "CD",            [KEY_TAPE] = "Tape",
    [KEY_RADIO] = "Radio",          [KEY_TUNER] = "Tuner",
    [KEY_PLAYER] = "Player",        [KEY_TEXT] = "Text",
    [KEY_DVD] = "DVD",          [KEY_AUX] = "Aux",
    [KEY_MP3] = "MP3",          [KEY_AUDIO] = "Audio",
    [KEY_VIDEO] = "Video",          [KEY_DIRECTORY] = "Directory",
    [KEY_LIST] = "List",            [KEY_MEMO] = "Memo",
    [KEY_CALENDAR] = "Calendar",        [KEY_RED] = "Red",
    [KEY_GREEN] = "Green",          [KEY_YELLOW] = "Yellow",
    [KEY_BLUE] = "Blue",            [KEY_CHANNELUP] = "ChannelUp",
    [KEY_CHANNELDOWN] = "ChannelDown",  [KEY_FIRST] = "First",
    [KEY_LAST] = "Last",            [KEY_AB] = "AB",
    [KEY_NEXT] = "Next",            [KEY_RESTART] = "Restart",
    [KEY_SLOW] = "Slow",            [KEY_SHUFFLE] = "Shuffle",
    [KEY_BREAK] = "Break",          [KEY_PREVIOUS] = "Previous",
    [KEY_DIGITS] = "Digits",        [KEY_TEEN] = "TEEN",
    [KEY_TWEN] = "TWEN",            [KEY_DEL_EOL] = "Delete EOL",
    [KEY_DEL_EOS] = "Delete EOS",       [KEY_INS_LINE] = "Insert line",
    [KEY_DEL_LINE] = "Delete line",
};

char *absval[5] = { "Value", "Min  ", "Max  ", "Fuzz ", "Flat " };

char *relatives[REL_MAX + 1] = {
    [0 ... REL_MAX] = NULL,
    [REL_X] = "X",          [REL_Y] = "Y",
    [REL_Z] = "Z",          [REL_HWHEEL] = "HWheel",
    [REL_DIAL] = "Dial",        [REL_WHEEL] = "Wheel", 
    [REL_MISC] = "Misc",    
};

char *absolutes[ABS_MAX + 1] = {
    [0 ... ABS_MAX] = NULL,
    [ABS_X] = "X",          [ABS_Y] = "Y",
    [ABS_Z] = "Z",          [ABS_RX] = "Rx",
    [ABS_RY] = "Ry",        [ABS_RZ] = "Rz",
    [ABS_THROTTLE] = "Throttle",    [ABS_RUDDER] = "Rudder",
    [ABS_WHEEL] = "Wheel",      [ABS_GAS] = "Gas",
    [ABS_BRAKE] = "Brake",      [ABS_HAT0X] = "Hat0X",
    [ABS_HAT0Y] = "Hat0Y",      [ABS_HAT1X] = "Hat1X",
    [ABS_HAT1Y] = "Hat1Y",      [ABS_HAT2X] = "Hat2X",
    [ABS_HAT2Y] = "Hat2Y",      [ABS_HAT3X] = "Hat3X",
    [ABS_HAT3Y] = "Hat 3Y",     [ABS_PRESSURE] = "Pressure",
    [ABS_DISTANCE] = "Distance",    [ABS_TILT_X] = "XTilt",
    [ABS_TILT_Y] = "YTilt",     [ABS_TOOL_WIDTH] = "Tool Width",
    [ABS_VOLUME] = "Volume",    [ABS_MISC] = "Misc",
};

char *misc[MSC_MAX + 1] = {
    [ 0 ... MSC_MAX] = NULL,
    [MSC_SERIAL] = "Serial",    [MSC_PULSELED] = "Pulseled",
    [MSC_GESTURE] = "Gesture",  [MSC_RAW] = "RawData",
    [MSC_SCAN] = "ScanCode",
};

char *leds[LED_MAX + 1] = {
    [0 ... LED_MAX] = NULL,
    [LED_NUML] = "NumLock",     [LED_CAPSL] = "CapsLock", 
    [LED_SCROLLL] = "ScrollLock",   [LED_COMPOSE] = "Compose",
    [LED_KANA] = "Kana",        [LED_SLEEP] = "Sleep", 
    [LED_SUSPEND] = "Suspend",  [LED_MUTE] = "Mute",
    [LED_MISC] = "Misc",
};

char *repeats[REP_MAX + 1] = {
    [0 ... REP_MAX] = NULL,
    [REP_DELAY] = "Delay",      [REP_PERIOD] = "Period"
};

char *sounds[SND_MAX + 1] = {
    [0 ... SND_MAX] = NULL,
    [SND_CLICK] = "Click",      [SND_BELL] = "Bell",
    [SND_TONE] = "Tone"
};

char **names[EV_MAX + 1] = {
    [0 ... EV_MAX] = NULL,
    [EV_SYN] = events,          [EV_KEY] = keys,
    [EV_REL] = relatives,           [EV_ABS] = absolutes,
    [EV_MSC] = misc,            [EV_LED] = leds,
    [EV_SND] = sounds,          [EV_REP] = repeats,
};

#define BITS_PER_LONG (sizeof(long) * 8)
#define NBITS(x) ((((x)-1)/BITS_PER_LONG)+1)
#define OFF(x)  ((x)%BITS_PER_LONG)
#define BIT(x)  (1UL<<OFF(x))
#define LONG(x) ((x)/BITS_PER_LONG)
#define test_bit(bit, array)    ((array[LONG(bit)] >> OFF(bit)) & 1)

int main (int argc, char **argv)
{
    int fd, rd, i, j, k;
    struct input_event ev[64];
    int version;
    unsigned short id[4];
    unsigned long bit[EV_MAX][NBITS(KEY_MAX)];
    char name[256] = "Unknown";
    int abs[5];

    if (argc < 2) {
        printf("Usage: evtest /dev/input/eventX\n");
        printf("Where X = input device number\n");
        return 1;
    }

    if ((fd = open(argv[argc - 1], O_RDONLY)) < 0) {
        perror("evtest");
        return 1;
    }

    if (ioctl(fd, EVIOCGVERSION, &version)) {
        perror("evtest: can't get version");
        return 1;
    }

    printf("Input driver version is %d.%d.%d\n",
        version >> 16, (version >> 8) & 0xff, version & 0xff);

    ioctl(fd, EVIOCGID, id);
    printf("Input device ID: bus 0x%x vendor 0x%x product 0x%x version 0x%x\n",
        id[ID_BUS], id[ID_VENDOR], id[ID_PRODUCT], id[ID_VERSION]);

    ioctl(fd, EVIOCGNAME(sizeof(name)), name);
    printf("Input device name: \"%s\"\n", name);

    memset(bit, 0, sizeof(bit));
    ioctl(fd, EVIOCGBIT(0, EV_MAX), bit[0]);
    printf("Supported events:\n");

    for (i = 0; i < EV_MAX; i++)
        if (test_bit(i, bit[0])) {
            printf("  Event type %d (%s)\n", i, events[i] ? events[i] : "?");
            if (!i) continue;
            ioctl(fd, EVIOCGBIT(i, KEY_MAX), bit[i]);
            for (j = 0; j < KEY_MAX; j++) 
                if (test_bit(j, bit[i])) {
                    printf("    Event code %d (%s)\n", j, names[i] ? (names[i][j] ? names[i][j] : "?") : "?");
                    if (i == EV_ABS) {
                        ioctl(fd, EVIOCGABS(j), abs);
                        for (k = 0; k < 5; k++)
                            if ((k < 3) || abs[k])
                                printf("      %s %6d\n", absval[k], abs[k]);
                    }
                }
        }


    printf("Testing ... (interrupt to exit)\n");
    while (1) {
        rd = read(fd, ev, sizeof(struct input_event) * 64);

        if (rd < (int) sizeof(struct input_event)) {
            printf("yyy\n");
            perror("\nevtest: error reading");
            return 1;
        }

        for (i = 0; i < rd / sizeof(struct input_event); i++)

            if (ev[i].type == EV_SYN) {
                printf("Event: time %ld.%06ld, -------------- %s ------------\n",
                    ev[i].time.tv_sec, ev[i].time.tv_usec, ev[i].code ? "Config Sync" : "Report Sync" );
            } else if (ev[i].type == EV_MSC && (ev[i].code == MSC_RAW || ev[i].code == MSC_SCAN)) {
                printf("Event: time %ld.%06ld, type %d (%s), code %d (%s), value %02x\n",
                    ev[i].time.tv_sec, ev[i].time.tv_usec, ev[i].type,
                    events[ev[i].type] ? events[ev[i].type] : "?",
                    ev[i].code,
                    names[ev[i].type] ? (names[ev[i].type][ev[i].code] ? names[ev[i].type][ev[i].code] : "?") : "?",
                    ev[i].value);
            } else {
                printf("Event: time %ld.%06ld, type %d (%s), code %d (%s), value %d\n",
                    ev[i].time.tv_sec, ev[i].time.tv_usec, ev[i].type,
                    events[ev[i].type] ? events[ev[i].type] : "?",
                    ev[i].code,
                    names[ev[i].type] ? (names[ev[i].type][ev[i].code] ? names[ev[i].type][ev[i].code] : "?") : "?",
                    ev[i].value);
            }   

    }
}

与此相当的C ++是什么?

0 个答案:

没有答案