1. Example (UDP Client)
// This program sends UDP packets to the given address
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#define SERVER_ADDR " "
#define SERVER_PORT 5555
void error(char *str) {
printf("\n%s", str);
exit(0); }
int main(int argc, char *argv[])
char message[100], message2[10];
int sockfd, res;
struct sockaddr_in client_addr, server_addr;
int i, mesNum;
printf("\nClient is running...");
if (argc < 2)
error("\nYou should supply parameter: the number of messages to send");

2. Example (UDP Client) // Opening socket
if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
error("Could not open socket");
// Sending a message to the server
bzero((char*) &server_addr, sizeof(server_addr));
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = inet_addr(SERVER_ADDR);
server_addr.sin_port = htons(SERVER_PORT);
mesNum = atoi(argv[1]);
if (mesNum == 0)
error("\nIllegal parameter");
for (i=0; i<mesNum; i++) {
strcpy(message, "Test message: ");
sprintf(message2, "%d", i+mesNum);
strcat(message, message2);
res = sendto(sockfd, message, strlen(message)+1, 0,
(struct sockaddr*)&server_addr, sizeof(server_addr));
printf("\nClient sent %d bytes", res); }

3. Example (UDP Server) // This program receives UDP packets
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#define SERVER_PORT 5555
#define MAX_MESSAGE_SIZE 100
void error(char *str) {
printf("\n%s", str);
exit(0); }
int main()
char message[MAX_MESSAGE_SIZE];
int sockfd, res;
struct sockaddr_in client_addr, server_addr;
int addr_len;
printf("\nServer is running..."); fflush(stdout);

4. Example (UDP Server) // Opening socket
if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
error("Could not open socket");
// Bind local ip and process addresses
bzero((char*) &server_addr, sizeof(server_addr));
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
server_addr.sin_port = htons(SERVER_PORT);
if (bind(sockfd, (struct sockaddr*)&server_addr, sizeof(server_addr)) < 0)
error("Could not bind to the socket");
while (1) {
// Receiving a message from the client
addr_len = sizeof(client_addr);
res = recvfrom(sockfd, message, MAX_MESSAGE_SIZE, 0, (struct sockaddr*)&client_addr, &addr_len);
printf("\nServer received %d bytes", res);
printf("\n%s", message); fflush(stdout); }