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<h1 class="topictitle1">Example: A connectionless client</h1>
<div><p>This example shows how to use User Datagram Protocol (UDP) to connect
a connectionless socket client program to a server.</p>
<div class="section"><div class="note"><span class="notetitle">Note:</span> By using the code examples, you agree to the terms
of the <a href="codedisclaimer.htm">Code license and disclaimer information</a>.</div>
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<div class="section"><pre>/**************************************************************************/
/* This sample program provides a code for a connectionless client. */
/**************************************************************************/
/**************************************************************************/
/* Header files needed for this sample program */
/**************************************************************************/
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
/**************************************************************************/
/* Constants used by this program */
/**************************************************************************/
#define SERVER_PORT 3555
#define BUFFER_LENGTH 100
#define FALSE 0
#define SERVER_NAME "ServerHostName"
/* Pass in 1 parameter which is either the */
/* address or host name of the server, or */
/* set the server name in the #define */
/* SERVER_NAME */
void main(int argc, char *argv[])
{
/***********************************************************************/
/* Variable and structure definitions. */
/***********************************************************************/
int sd, rc;
char server[NETDB_MAX_HOST_NAME_LENGTH];
char buffer[BUFFER_LENGTH];
struct hostent *hostp;
struct sockaddr_in serveraddr;
int serveraddrlen = sizeof(serveraddr);
/***********************************************************************/
/* A do/while(FALSE) loop is used to make error cleanup easier. The */
/* close() of the socket descriptor is only done once at the very end */
/* of the program. */
/***********************************************************************/
do
{
/********************************************************************/
/* The socket() function returns a socket descriptor representing */
/* an endpoint. The statement also identifies that the INET */
/* (Internet Protocol) address family with the UDP transport */
/* (SOCK_STREAM) will be used for this socket. */
/********************************************************************/
sd = socket(AF_INET, SOCK_DGRAM, 0);
if (sd < 0)
{
perror("socket() failed");
break;
}
/********************************************************************/
/* If an argument was passed in, use this as the server, otherwise */
/* use the #define that is located at the top of this program. */
/********************************************************************/
if (argc > 1)
strcpy(server, argv[1]);
else
strcpy(server, SERVER_NAME);
memset(&serveraddr, 0, sizeof(serveraddr));
serveraddr.sin_family = AF_INET;
serveraddr.sin_port = htons(SERVER_PORT);
serveraddr.sin_addr.s_addr = inet_addr(server);
if (serveraddr.sin_addr.s_addr == (unsigned long)INADDR_NONE)
{
/*****************************************************************/
/* The server string that was passed into the inet_addr() */
/* function was not a dotted decimal IP address. It must */
/* therefore be the hostname of the server. Use the */
/* gethostbyname() function to retrieve the IP address of the */
/* server. */
/*****************************************************************/
hostp = gethostbyname(server);
if (hostp == (struct hostent *)NULL)
{
printf("Host not found --> ");
printf("h_errno = %d\n", h_errno);
break;
}
memcpy(&serveraddr.sin_addr,
hostp->h_addr,
sizeof(serveraddr.sin_addr));
}
/********************************************************************/
/* Initialize the data block that is going to be sent to the server */
/********************************************************************/
memset(buffer, 0, sizeof(buffer));
strcpy(buffer, "A CLIENT REQUEST");
/********************************************************************/
/* Use the sendto() function to send the data to the server. */
/********************************************************************/
rc = sendto(sd, buffer, sizeof(buffer), 0,
(struct sockaddr *)&serveraddr,
sizeof(serveraddr));
if (rc < 0)
{
perror("sendto() failed");
break;
}
/********************************************************************/
/* Use the recvfrom() function to receive the data back from the */
/* server. */
/********************************************************************/
rc = recvfrom(sd, buffer, sizeof(buffer), 0,
(struct sockaddr *)&serveraddr,
& serveraddrlen);
if (rc < 0)
{
perror("recvfrom() failed");
break;
}
printf("client received the following: <%s>\n", buffer);
printf("from port %d, from address %s\n",
ntohs(serveraddr.sin_port),
inet_ntoa(serveraddr.sin_addr));
/********************************************************************/
/* Program complete */
/********************************************************************/
} while (FALSE);
/***********************************************************************/
/* Close down any open socket descriptors */
/***********************************************************************/
if (sd != -1)
close(sd);
}</pre>
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<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="connectionless.htm" title="Connectionless sockets do not establish a connection over which data is transferred. Instead, the server application specifies its name where a client can send requests.">Create a connectionless socket</a></div>
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