This is sockets/t_gethostbyname.c (Listing 59-10, page 1233), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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/* t_gethostbyname.c

   Demonstrate the use of gethostbyname() to lookup of the address for a
   given host name. Note that gethostbyname() is now obsolete; new programs
   should use getaddrinfo().
#if defined(_AIX)       /* AIX 5.1 needs this to get hstrerror() declaration */
#define _USE_IRS
#define _BSD_SOURCE     /* To get hstrerror() declaration from <netdb.h> */
#include <netdb.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include "tlpi_hdr.h"
main(int argc, char *argv[])
    struct hostent *h;
    char **pp;
    char str[INET6_ADDRSTRLEN];

    for (argv++; *argv != NULL; argv++) {
        h = gethostbyname(*argv);
        if (h == NULL) {
            fprintf(stderr, "gethostbyname() failed for '%s': %s\n",
                    *argv, hstrerror(h_errno));

        printf("Canonical name: %s\n", h->h_name);

        printf("        alias(es):     ");
        for (pp = h->h_aliases; *pp != NULL; pp++)
            printf(" %s", *pp);

        printf("        address type:   %s\n",
                (h->h_addrtype == AF_INET) ? "AF_INET" :
                (h->h_addrtype == AF_INET6) ? "AF_INET6" : "???");

        if (h->h_addrtype == AF_INET || h->h_addrtype == AF_INET6) {
            printf("        address(es):   ");
            for (pp = h->h_addr_list; *pp != NULL; pp++)
                printf(" %s", inet_ntop(h->h_addrtype, *pp,
                                        str, INET6_ADDRSTRLEN));



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