将#define置于结构中

struct gpio_desc {
    struct gpio_chip    *chip;
    unsigned long       flags;
/* flag symbols are bit numbers */
#define FLAG_REQUESTED  0
#define FLAG_IS_OUT 1
#define FLAG_EXPORT 2   /* protected by sysfs_lock */
#define FLAG_SYSFS  3   /* exported via /sys/class/gpio/control */
#define FLAG_ACTIVE_LOW 6   /* value has active low */
#define FLAG_OPEN_DRAIN 7   /* Gpio is open drain type */
#define FLAG_OPEN_SOURCE 8  /* Gpio is open source type */
#define FLAG_USED_AS_IRQ 9  /* GPIO is connected to an IRQ */
#define FLAG_IS_HOGGED  11  /* GPIO is hogged */

    /* Connection label */
    const char      *label;
    /* Name of the GPIO */
    const char      *name;
};

将定义放入结构体中的原因是什么？