How to set the source port in the UDP socket in c?

Question

Can any one tell me how to set the Source port address in the UDP socket ?. My client application needs to send the Packets from the 57002 port to the server port 58007 .

Answer 1

struct sockaddr_in servaddr,cliaddr;
sockfd=socket(AF_INET,SOCK_DGRAM,0);

servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr=inet_addr(argv[1]);
servaddr.sin_port=htons(32000); //destination port for incoming packets


cliaddr.sin_family = AF_INET;
cliaddr.sin_addr.s_addr= htonl(INADDR_ANY);
cliaddr.sin_port=htons(33000); //source port for outgoing packets
bind(sockfd,(struct sockaddr *)&cliaddr,sizeof(cliaddr));



use sendto with servaddr 
use recvfrom with cliaddr
if u check wireshark u will see source port as 33000 and destination port as 32000 for sendto operation

Answer 2

bind(2) it. Use INADDR_ANY address and your port number.

Answer 3

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

#define DST_PORT    58007
#define SRC_PORT    57002

#define IP      "127.0.0.1"

int main(int argc, char *argv[]) {
    struct sockaddr_in addr, srcaddr;
    int fd;
    char message[] = "Hello, World!";

    if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
        perror("socket");
        exit(1);
    }

    memset(&addr, 0, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = inet_addr(IP);
    addr.sin_port = htons(DST_PORT);

    memset(&srcaddr, 0, sizeof(srcaddr));
    srcaddr.sin_family = AF_INET;
    srcaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    srcaddr.sin_port = htons(SRC_PORT);

    if (bind(fd, (struct sockaddr *) &srcaddr, sizeof(srcaddr)) < 0) {
        perror("bind");
        exit(1);
    }

    while (1) {
        if (sendto(fd, message, sizeof(message), 0, (struct sockaddr *) &addr,
                sizeof(addr)) < 0) {
            perror("sendto");
            exit(1);
        }
        sleep(1);
    }
    return 0;
}

Answer 4

 struct sockaddr_in sa;
 int ret, fd;

 memset(&sa, 0, sizeof(struct sockaddr_in));
 sa.sin_family = AF_INET;
 sa.sin_port = htons(LOCAL_PORT);
 sa.sin_addr.s_addr = inet_addr(LOCAL_IP_ADDRESS);


 ret = bind(fd, (struct sockaddr *)&sa, sizeof(struct sockaddr));