The profoundness of C language: assignment operations of arrays and structures-EEWORLD

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First, let's talk about array assignment. Well, in C language, array assignment and structure assignment are very simple, just use = and memcpy operations.

But recently, when I was looking at the kernel implementation code for queue scheduling, I found the following strange assignment statement. (For the specific program, see line 539 of linux-2.6.8:net/core/Rtnetlink.c)

#define RTM_MAX (RTM_BASE+47)
#define RTM_GETLINK (RTM_BASE+2)
struct rtnetlink_link
{
int (*doit)(struct sk_buff *, struct nlmsghdr*, void *attr);
int (*dumpit)(struct sk_buff *, struct netlink_callback *cb);
};
static struct rtnetlink_link link_rtnetlink_table[RTM_MAX-RTM_BASE+1] =
//RTM_MAX-RTM_BASE+1=48
{
[RTM_GETLINK - RTM_BASE] = { .dumpit = rtnetlink_dump_ifinfo },
[RTM_SETLINK - RTM_BASE] = { .doit = do_setlink },
[RTM_GETADDR - RTM_BASE] = { .dumpit = rtnetlink_dump_all },
[RTM_GETROUTE - RTM_BASE] = { .dumpit = rtnetlink_dump_all },
[RTM_NEWNEIGH - RTM_BASE] = { .doit = neigh_add },
[RTM_DELNEIGH - RTM_BASE] = { .doit = neigh_delete },
[RTM_GETNEIGH - RTM_BASE] = { .dumpit = neigh_dump_info }
};

This is the first time I have seen the assignment statement above. After reading it for a long time, I finally understood the meaning of this assignment statement. It turns out that C language can also assign values in this way.

Note: There are two things to note about the above assignment statement.

1, [RTM_GETLINK - RTM_BASE] = { .dumpit = rtnetlink_dump_ifinfo }, This indicates that when assigning values to an array, the C language can assign values to the element in question. In this example, it is equal to [2] = {...}, which means assigning values to the second element.

2. { .dumpit = rtnetlink_dump_ifinfo } indicates that, in the structure assignment, a specific structure member can also be assigned separately.

Reference address：The profoundness of C language: assignment operations of arrays and structures

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