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

#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;
}