c - int 指针指向两个结构体指针？

Question

这是来自 linux 构建文件 <linux/usb/serial.h> :

int (*calc_num_ports)(struct usb_serial *serial, struct usb_serial_endpoints *epds);

我只是有点无法理解这里发生的事情。一个 int 指针指向两个结构体指针？这是如何运作的？

Answer 1

它告诉您它是什么以及它在 header ( <linux/usb/serial.h> ) 中的用途:

@calc_num_ports: pointer to a function to determine how many ports this *  device has dynamically. It can also be used to verify the number of *  endpoints or to modify the port-endpoint mapping. It will be called *  after the probe() callback is called, but before attach().

The syntax for a function pointer is not very intuitive. Consider the following:

int *calc_num_ports(struct usb_serial *serial, struct usb_serial_endpoints *epds);
int (*calc_num_ports)(struct usb_serial *serial, struct usb_serial_endpoints *epds);

第一个是名为calc_num_ports的函数的原型(prototype)需要两个参数，struct usb_serial *和struct usb_serial_endpoints * ，和return是 int * .

第二个是变量类型，需要带有两个参数的函数的地址，struct usb_serial *和struct usb_serial_endpoints *和return是 int .