Why we use memset to fill the structure with value 0, in socket programming c?

Question

struct sockaddr_in servaddr, cliaddr; 

// Creating socket file descriptor 
if ( (sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) { 
    perror("socket creation failed"); 
    exit(EXIT_FAILURE); 
} 

memset(&servaddr, 0, sizeof(servaddr)); 
memset(&cliaddr, 0, sizeof(cliaddr));

In my previous work on structs i didn't fill the structures with value 0, but here in socket we always reset, fill 0, the struct before using it. Why is it important to fill 0 the structure?

Answer 1

Unless the variables are declared as static storage duration, they will have an arbitrary value upon creation. Hence, it's always a good idea to set them to a known value before using them.

For example, if your next step after socket() is a connect() or bind(), they will very much want a specific structure value for client or server respectively.

It's no different really to the function:

void xyzzy(void) {
    int plugh;
    printf("%d\n", plugh);
}

inasmuch as it may print any value.