struct sockaddr_in 
{
    sa_family_t    sin_family; /* address family: AF_INET */
    in_port_t      sin_port;   /* port in network byte order */
    struct in_addr sin_addr;   /* internet address */
};

/* Internet address. */
struct in_addr 
{
    uint32_t       s_addr;     /* address in network byte order */
};

#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <arpa/inet.h>

int 
main()
{
    const char *ip_str = "192.168.1.1";
    //const char *ip_str = "255.255.255.255";
    //const char *ip_str = "0.0.0.0";
    struct in_addr in;
    memset(&in, 0, sizeof(struct in_addr));
    in.s_addr = inet_addr(ip_str);    
    printf("ip addr is:%u\n", in.s_addr);
    printf("ip addr is:%s\n", inet_ntoa(in));
    memset(&in, 0, sizeof(struct in_addr));
    inet_aton(ip_str, &in);
    printf("ip addr is:%s\n", inet_ntoa(in));
    return 0;
}

shelmean:[~]$ ./a.out 
ip addr is:16885952
ip addr is:192.168.1.1
ip addr is:192.168.1.1