Probe into the usage of gethostbyname () and getaddrinfo ()

The main is how to use the return structure of two functions. In the GetHostByName function, the return Hostent,linux reference manual is described below:

struct hostent {    char  *h_name;            /* official name of host */    char **h_aliases;         /* alias list */    int    h_addrtype;        /* host address type */    int    h_length;          /* length of address */    char **h_addr_list;       /* list of addresses */}

The specific usage can be seen in the following code:

#include <arpa/inet.h>#include <netdb.h>#include <stdlib.h>#include <stdio.h>intMainintargcChar* argv[]) {Char*ptr, **pptr;CharStr[inet_addrstrlen];structHostent * HPTR; while(--ARGC >0) {ptr = *++argv;if((hptr = gethostbyname (ptr)) = = NULL) {fprintf(stderr,"gethostbyname error for host%s:%s", PTR, Hstrerror (H_errno));Continue; }printf("Official hostname%s\n", hptr->h_name); for(pptr = hptr->h_aliases; *pptr! = NULL; ++pptr)printf("\talials:%s\n", *pptr);Switch(Hptr->h_addrtype) { CaseAf_inet:pptr = hptr->h_addr_list; for(; *pptr! = NULL; ++pptr)printf("\taddress:%s\n", Inet_ntop (Hptr->h_addrtype, *pptr, str,sizeof(str))); Break;default:fprintf(stderr,"Unknown address type");Exit(exit_failure); Break; }    }return 0;}

./hostent www.baidu.comafter execution
The effect is as follows:

The Getaddrinfo function is more complex, but provides a better interface.
This is just a sample program to show.

#include <stdio.h>#include <stdlib.h>#include <string.h>#include <sys/socket.h>#include <netdb.h>#include <sys/types.h>#include <arpa/inet.h>voidPrintaddressinfo (Const structaddrinfo*);intMainintargcChar* argv[]) {intNstructaddrinfo* Res, *ressave;structAddrinfo hint;Char* SERV;if(ARGC <2)    {fprintf(stderr,"Usage:"                "./getaddrinfo                 "or Port name>]\n");Exit(exit_failure); }if(ARGC = =2) serv = NULL;Elseserv = argv[2]; Bzero (&hint,sizeof(hint)); hint.ai_family = Af_unspec;if((n = getaddrinfo (argv[1], serv, &hint, &res)! =!0)    {if(Argc >2)fprintf(stderr,"Cannot get information for"                    "%s:%s\n\terror:%s\n", argv[1], serv, Gai_strerror (n));Else            fprintf(stderr,"Cannot get information for"                    "%s\n\terror:%s\n", argv[1], Gai_strerror (n));Exit(exit_failure); } ressave = res; while(res! = NULL)        {Printaddressinfo (res);    res = res->ai_next; } freeaddrinfo (Ressave);Exit(exit_success);}voidPrintaddressinfo (Const structaddrinfo* addr) {CharStr[inet6_addrstrlen]; ShortPortprintf("ai_family:");Switch(addr->ai_family) { CaseAf_inet: {structSockaddr_in* in;printf("ipv4\n"); in = (structsockaddr_in *) (ADDR-&GT;AI_ADDR);            Port = Ntohs (In->sin_port); Inet_ntop (af_inet, &in->sin_addr, str,sizeof(str)); Break; } CaseAf_inet6: {structsockaddr_in6* in6; In6 = (structSOCKADDR_IN6 *) (ADDR-&GT;AI_ADDR);            Port = Ntohs (In6->sin6_port); Inet_ntop (AF_INET6, &in6->sin6_addr, str,sizeof(str));printf("ipv6\n"); Break; }default:printf("unknown\n"); Break; }printf("Ai_socktype:");Switch(Addr->ai_socktype) { CaseSock_stream:printf("stream\n"); Break; CaseSock_dgram:printf("dgram\n"); Break; CaseSock_seqpacket:printf("seqpacket\n"); Break; CaseSock_raw:printf("raw\n"); Break;default:printf("others\n"); Break; }printf("Protocol:");Switch(Addr->ai_protocol) { CaseIPPROTO_TCP:printf("Tcp\n"); Break; CaseIPPROTO_UDP:printf("Udp\n"); Break; CaseIPPROTO_SCTP:printf("Sctp\n"); Break;default:printf("others\n"); Break; }printf("Address:%s\n", str);printf("Port:%d\n", port);printf("canonical name:%s\n\n", addr->ai_canonname);}

The above procedure after entering: ./getaddrinfo www.baidu.com http , the effect is as follows:

The focus is on the display of the address. The contents of the structure.

Probe into the usage of gethostbyname () and getaddrinfo ()