Rp is a pointer to a structure (or a pointer to another whole). It points to a structure that is equivalent to your home address.

Nr_running is a member of the structure pointed by rp, such as your home 1 room.

RP-& gt； Nr_running is your room 1.

The function of "."is similar to that of "->"

"."is preceded by variable name (or other names) and "->", followed by address and pointer.

For example, your home, Room xx, Building xx, District xx. 1-> 1 room

void*(*start_rtn)(void)

A pointer to a function is defined, and the pointer should correspond to the parameter return value of the function.

In other words, the parameter of the function pointed by this pointer is void, and the return value is void pointer.

Define the form of function pointer,,,

void* (*start_rtn) (void)

The parameter of the function pointed by the name of the function pointer defined by the return value of the function to point to.

int ms(int msgid，stuct msgbuf *msp)

A function whose return value is an integer is defined. This function has two parameters, int msgid. The first parameter is an int type named msgid. Stuct msgbuf *msp, and the second parameter is a pointer MSP of Stuct msgbuf type;

Struct msgbuf can be abbreviated as msgbuf.