UNIX & GNU/Linux - System calls - Using bind()

The bind() system call function is used with socket().

It assigns the address of the second argument to the file descriptor retrieved by socket().
Of course before using bind(), we must have a valid fd generated by socket().

Using bind()

server.c

/* server.c */
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <netinet/in.h>

#include "h.h"

void my_socket(t_s *s)
{
    s->name    = "TCP";
    s->domain    = AF_INET;
    s->type    = SOCK_STREAM;
    s->pe        = getprotobyname(s->name);
    s->fd        = socket(s->domain, s->type, s->pe->p_proto);
    check_error(s->fd, -1);
}

void my_bind(t_s *s, int port)
{
    s->sockfd                = s->fd;
    s->addr.sin_family        = s->domain;
    s->addr.sin_addr.s_addr = INADDR_ANY;
    s->addr.sin_port        = htons(port);
    s->addrlen                = sizeof(s->addr);
    s->bindValue            = bind(s->fd, (const struct sockaddr *)&s->addr, s->addrlen);
    check_error(s->bindValue, -1);
}

int main(int ac, char *av[])
{
    t_s s;

    check_arg(ac, 2);
    my_socket(&s);
    my_bind(&s, atoi(av[1]));
    debug(&s);
    check_error(close(s.fd), -1);
    return 0;
}

debug.c

/* debug.c */
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <unistd.h>

#include "h.h"

void debug(t_s *s)
{
    printf("\n===== socket() =====\n");
    printf("domain = %d\n", s->domain);
    printf("type = %d\n", s->type);
    printf("fd = %d\n", s->fd);
    printf("name = %s\n", s->name);
    printf("p_proto = %d\n", s->pe->p_proto);

    printf("\n===== bind() =====\n");
    printf("sockfd = %d\n", s->sockfd);
    printf("sin_family = %d\n", s->addr.sin_family);
    printf("sin_addr.s_addr = %d\n", s->addr.sin_addr.s_addr);
    printf("sin_port = %d\n", s->addr.sin_port);
    printf("addrlen = %d\n", s->addrlen);
    printf("bindValue = %d\n\n", s->bindValue);
}

void check_error(int test, int error)
{
    if (test == error)
    {
        fprintf(stderr, "ERROR: %s\n", strerror(errno));
        exit(EXIT_FAILURE);
    }
}

void check_arg(int ac, int number)
{
    if (ac < number)
    {
        printf("Usage: ./server [PORT]\n");
        exit(EXIT_FAILURE);
    }
}

h.h

#ifndef H_H_
#define H_H_

#include <netdb.h>

/**
 * Structure
 */
typedef struct mystruct
{
    int domain;
    int type;
    int fd;
    char *name;
    struct protoent *pe;

    int sockfd;
    socklen_t addrlen;
    struct sockaddr_in addr;
    int bindValue;
} t_s;

/**
 * Prototype
 */
void debug(t_s *);
void check_error(int, int);
void check_arg(int, int);

#endif /* H_H_ */

Compiling

$ gcc server.c debug.c -o server ; ./server 5000

Result

===== socket() =====
domain = 2
type = 1
fd = 3
name = TCP
p_proto = 6

===== bind() =====
sockfd = 3
sin_family = 2
sin_addr.s_addr = 0
sin_port = 34835
addrlen = 16
bindValue = 0

Good job!