Linux C network programming: Use domain name to obtain IP address or IP to get the domain name network address conversion to integer host character sequence and network byte order conversion

Get an IP address with a domain name or get a domain name with IP

#include<stdio.h>
#include<sys/socket.h>
#include<netdb.h>
int main(int argc,char **aggv)
{
        struct hostent *host;
        char hostname[]="www.163.com";
        char hostname2[]="www.baidu.com";
        struct in_addr in;
        struct sockaddr_in addr_in;
        int h_errno;
        char addr[]="202.108.249.216";

        if((host=gethostbyname(hostname))!=NULL)
                {
                        memcpy(&addr_in.sin_addr.s_addr,host->h_addr,4);
                        in.s_addr=addr_in.sin_addr.s_addr;
                        printf("Domain name : %s \n",hostname);
                        printf("IP length is: %d \n",host->h_length);
                        printf("Type : %d \n",host->h_addrtype);
                        printf("IP : %s \n",inet_ntoa(in));

                }

        if(((host=gethostbyaddr(addr,sizeof(addr),AF_INET)))!=(struct hostnet *)NULL)
        {
                memcpy(&addr_in.sin_addr.s_addr,host->h_addr,4);
                        in.s_addr=addr_in.sin_addr.s_addr;
                        printf("\n---------------------\n");
                        printf("Domain name : %s \n",hostname);
                        printf("IP length is: %d \n",host->h_length);
                        printf("Type : %d \n",host->h_addrtype);
                        printf("IP : %s \n",inet_ntoa(in));
        }
        return 0;
}

#include <stdio.h>
#include <netdb.h>
#include <arpa / inet.h>
int main ()
{
         int i;
         for (i = 0; i <6; i ++)
         printf ("% d% s \ n", i, hstrerror (i)); // Catch the error number

         char cp [] = "192.168.0.84";
         printf ("% ld \ n", inet_addr (cp));
// Convert network address to integer
  struct in_addr ip; ip.s_addr = 16885952; printf ("% s \ n", inet_ntoa (ip));
// Convert integer to network address
  long local; int port; local = 123456; port = 1024; printf ("net:% d \ n", htonl (local)); // Conversion of host character order and network byte order printf ("net:% d \ n ", htonl (port)); printf (" local:% d \ n ", ntohl (htonl (local)));
  printf ("local:% d \ n", ntohl (htonl (port))); return 0;}