Hi all,
I have written socket programs udpServer.c and udpClient.c . In which i write client code as

sendagain:
rc = sendto(sd,sendtext, strlen(sendtext)+1, 0,(struct sockaddr *) &remoteServAddr, sizeof(remoteServAddr));

if(rc<0) {
printf("cannot send data \n");
close(sd);
exit(1);
}
memset(msg,0x0,1024);
cliLen = sizeof(cliAddr);
n = recvfrom(sd, recvtext, 1024, 0, (struct sockaddr *) &cliAddr, &cliLen);
if(strcmp(senttext,recvtext)!=0)
goto sendagain;

my client programs sends string to server and server sends same string back to client then client compares if both sent and received string is same or not?
if not same then i am sending same string again to server by using goto.

What i am trying to configure my udpclient work as nonblocking with timeout 5seconds.
how then can i code condition of making sockets nonblocking and only block for 5 seconds here.

Probably the best way is to select(2) or poll(2) on the file descriptor with a timeout of 5 seconds. If the socket has no data after those 5 seconds (you'll need to check the output of select and poll, see the man pages for exact details), act accordingly.

OK Finally i swapped my server and clients codes. But i am unable to use select in my udpserver program that generates string and sends to clients and clients back to server.
Please help me to make following program as UDPSERVER which is actually tcpserver program with select call used.

#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/time.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>

#define LOCAL_SERVER_PORT 9200

int main()
{
int server_sockfd, client_sockfd;
int server_len, client_len;
struct sockaddr_in server_address;
struct sockaddr_in client_address;
int result;
fd_set readfds, testfds;
unsigned char msg[1024],recvtext[1024],sendtext[1024];
struct timeval timeout;
strcpy(sendtext,"mystring");


server_sockfd = socket(AF_INET, SOCK_DGRAM, 0);

server_address.sin_family = AF_INET;
server_address.sin_addr.s_addr = htonl(INADDR_ANY);
server_address.sin_port = htons(1500);
server_len = sizeof(server_address);

bind(server_sockfd, (struct sockaddr *)&server_address, server_len);


listen(server_sockfd, 5);

FD_ZERO(&readfds);
FD_SET(server_sockfd, &readfds);


while(1) {

int fd;
int nread;
int rc, n;
timeout.tv_sec = 5;
timeout.tv_usec = 000000;

testfds = readfds;

printf("server waiting\n");
result = select(FD_SETSIZE, &testfds, (fd_set *)0,
(fd_set *)0, &timeout);

if(result < 1) {
perror("server5");
exit(1);
}


for(fd = 0; fd < FD_SETSIZE; fd++) {
if(FD_ISSET(fd,&testfds)) {


if(fd == server_sockfd) {
client_len = sizeof(client_address);
client_sockfd = accept(server_sockfd,
(struct sockaddr *)&client_address, &client_len);
FD_SET(client_sockfd, &readfds);
printf("adding client on fd %d\n", client_sockfd);
}

else {
ioctl(fd, FIONREAD, &nread);

if(nread == 0) {
close(fd);
FD_CLR(fd, &readfds);
printf("removing client on fd %d\n", fd);
}

else {
sendagain:
rc = sendto(fd,sendtext, strlen(sendtext)+1, 0,(struct sockaddr *) &server_address, sizeof(server_address));

if(rc<0) {
printf("cannot send data \n");
close(fd);
exit(1);
}
memset(msg,0x0,1024);
client_len = sizeof(client_address);
n = recvfrom(fd, recvtext, 1024, 0, (struct sockaddr *) &client_address, &client_len);
if(strcmp(senttext,recvtext)!=0)
goto sendagain;
}
}
}
}
}
}