/* dgramclnt.c: *  * Example datagram client : */#include <stdio.h>#include <unistd.h>#include <stdlib.h>#include <errno.h>#include <string.h>#include <time.h>#include <sys/types.h>#include <sys/socket.h>#include <netinet/in.h>#include <arpa/inet.h>/* * This function reports the error and * exits back to the shell : */static voidbail(const char *on_what) {    fputs(strerror(errno),stderr);    fputs(": ",stderr);    fputs(on_what,stderr);    fputc('\n',stderr);    exit(1);}intmain(int argc,char **argv) {    int z;    int x;    char *srvr_addr = NULL;    struct sockaddr_in adr_srvr;/* AF_INET */    struct sockaddr_in adr;     /* AF_INET */    int len_inet;               /* length  */    int s;                       /* Socket */    char dgram[512];        /* Recv buffer */    /*     * Use a server address from the command     * line, if one has been provided.     * Otherwise, this program will default     * to using the arbitrary address     * 127.0.0.23 :     */    if ( argc >= 2 ) {        /* Addr on cmdline: */        srvr_addr = argv[1];    } else {        /* Use default address: */        srvr_addr = "127.0.0.23";    }    /*     * Create a socket address, to use     * to contact the server with:     */    memset(&adr_srvr,0,sizeof adr_srvr);    adr_srvr.sin_family = AF_INET;    adr_srvr.sin_port = htons(9090);    adr_srvr.sin_addr.s_addr =        inet_addr(srvr_addr);    if ( adr_srvr.sin_addr.s_addr == INADDR_NONE )        bail("bad address.");    len_inet = sizeof adr_srvr;    /*     * Create a UDP socket to use :     */    s = socket(AF_INET,SOCK_DGRAM,0);    if ( s == -1 )        bail("socket()");    for (;;) {        /*         * Prompt user for a date format string:         */        fputs("\nEnter format string: ",stdout);        if ( !fgets(dgram,sizeof dgram,stdin) )            break;                        /* EOF */        z = strlen(dgram);        if ( z > 0 && dgram[--z] == '\n' )            dgram[z] = 0;   /* Stomp out newline */        /*         * Send format string to server:         */        z = sendto(s,   /* Socket to send result */            dgram, /* The datagram result to snd */            strlen(dgram), /* The datagram lngth */            0,              /* Flags: no options */            (struct sockaddr *)&adr_srvr,/* addr */            len_inet);  /* Server address length */        if ( z < 0 )            bail("sendto(2)");        /*         * Test if we asked for a server shutdown:         */        if ( !strcasecmp(dgram,"QUIT") )            break;          /* Yes, we quit too */        /*         * Wait for a response :         */        x = sizeof adr;        z = recvfrom(s,                /* Socket */            dgram,           /* Receiving buffer */            sizeof dgram,   /* Max recv buf size */            0,              /* Flags: no options */            (struct sockaddr *)&adr,     /* Addr */            &x);           /* Addr len, in & out */        if ( z < 0 )            bail("recvfrom(2)");        dgram[z] = 0;          /* null terminate */        /*         * Report Result :         */        printf("Result from %s port %u :\n\t'%s'\n",            inet_ntoa(adr.sin_addr),            (unsigned)ntohs(adr.sin_port),            dgram);    }    /*     * Close the socket and exit:     */    close(s);    putchar('\n');    return 0;}