Question

我编写了以下代码来处理Linux上的操纵杆：

static int fd;

int joystick_init(void)
{
    struct js_event event;

    if((fd = open("/dev/input/js1", O_RDONLY | O_NONBLOCK)) == -1)
        return ERROR;

    //ignore all init events
    while(read(fd, &event, sizeof(struct js_event)) == sizeof(struct js_event)){
    }

    return SUCCESS;
}

void joystick_end(void)
{
    close(fd);
}

const struct js_event *joystick_get_event(void)
{
    static struct js_event event;

    if(read(fd, &event, sizeof(struct js_event)) == sizeof(struct js_event))
        return &event;

    return NULL;
}

以下内容打印事件：

void joy_input(const struct js_event *event)
{
    switch(event->type){
        case JS_EVENT_BUTTON:
            printf("button number = %d\n", event->number);
            break;

        case JS_EVENT_AXIS:
            printf("axis number = %d\n", event->number);
            break;
    }

    printf("event time = %d\n", event->time);
    printf("event value = %d\n", event->value);
    printf("event type = %d\n", event->type);
    puts("joy_input called");
}

这是每次按下按钮时打印的内容：

活动时间= 6348112

事件值= 0

事件类型= 0

joy_input调用

问题是什么？为什么不报告JS_EVENT_BUTTON或JS_EVENT_AXIS？为什么时间不变？

修改

//void * can't point to functions
typedef struct Joystick_Listener {
    void (*cb)(const struct js_event *event);
} Joystick_Listener;

static void dispatch_joy_events(Node *node, void *arg)
{
    Joystick_Listener *listener = node->content;
    listener->cb(arg);
}

void video_and_input_run(void)
{
    const struct js_event *event;

    while(1){
        /* ... */

        //Call joystick listeners
        pthread_mutex_lock(&joy_listener_lock);

        while((event = joystick_get_event()) != NULL)
            list_iterate_arg(&joy_listener, dispatch_joy_events, &event);

        pthread_mutex_unlock(&joy_listener_lock);

        /* ... */
    }
}

void list_iterate_arg(const List *list, void(*function)(Node*, void *), void *arg)
{
    Node *next; //store in case the node changes
    for(Node *ite = list->first; ite != NULL; ite = next){
        next = ite->next;
        function(ite, arg);
    }
}

Answer 1

愚蠢的错误，我传递了event的地址，但它已经是事件的指针，而不是事件本身，所以没有任何意义。

void video_and_input_run(void)
{
    const struct js_event *event;

    while(1){
        /* ... */

        //Call joystick listeners
        pthread_mutex_lock(&joy_listener_lock);

        while((event = joystick_get_event()) != NULL)
            list_iterate_arg(&joy_listener, dispatch_joy_events, event);

        pthread_mutex_unlock(&joy_listener_lock);

        /* ... */
    }
}

为什么js_event.type始终为0？

1 个答案: