下面的 C 代码有什么作用，= { }

Question

The code below is contained in STMicroelectronics C code for a USB driver. I am trying to follow (understand) how this works, and I admit my C programming is not strong.

My question is what does / is

USBD_Interface_fops_FS =
{ xxxxx }

???

I cannot find in K & R, where the "=" assignment operator is used in a similar example.

typedef struct _USBD_CDC_Itf
{
  int8_t (* Init)          (void);
  int8_t (* DeInit)        (void);
  int8_t (* Control)       (uint8_t, uint8_t * , uint16_t);   
  int8_t (* Receive)       (uint8_t *, uint32_t *);  

}USBD_CDC_ItfTypeDef;

static int8_t CDC_Init_FS     (void);
static int8_t CDC_DeInit_FS   (void);
static int8_t CDC_Control_FS  (uint8_t cmd, uint8_t* pbuf, uint16_t length);
static int8_t CDC_Receive_FS  (uint8_t* pbuf, uint32_t *Len);

USBD_CDC_ItfTypeDef USBD_Interface_fops_FS = 
{
  CDC_Init_FS,
  CDC_DeInit_FS,
  CDC_Control_FS,  
  CDC_Receive_FS
};

Answer 1

It's struct initializer syntax . It's just setting the four function pointers in the struct to the four named functions.

Answer 2

Struct initialization.

This:

USBD_CDC_ItfTypeDef USBD_Interface_fops_FS = 
{
  CDC_Init_FS,
  CDC_DeInit_FS,
  CDC_Control_FS,  
  CDC_Receive_FS
};

is just a more efficient way of doing this:

USBD_CDC_ItfTypeDef USBD_Interface_fops_FS;
USBD_Interface_fops_FS.Init = CDC_Init_FS;
USBD_Interface_fops_FS.DeInit = CDC_DeInit_FS;
USBD_Interface_fops_FS.Control = CDC_Control_FS;
USBD_Interface_fops_FS.Receive = CDC_Receive_FS;

I know for sure that this has been around since ANSI C 89. I don't know if they had struct initialization in K & R though...