C ++套接字不断接收相同的数据

Question

I am using this code to receive data from a sensor through sockets. The problem is that I keep receiving the same output for every iteration of the for loop. However I receive a different number for every time I run the code but again, the same number keeps repeating. The sensor should send different every time data but thats not the case here.

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <netdb.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include "port.h"

#define BUFSIZE 2048

int
main(int argc, char **argv)
{
    struct sockaddr_in myaddr;  /* our address */
    struct sockaddr_in remaddr; /* remote address */
    socklen_t addrlen = sizeof(remaddr);        /* length of addresses */
    int recvlen;            /* # bytes received */
    int fd;             /* our socket */
    int msgcnt = 0;         /* count # of messages we received */
    unsigned char buf[BUFSIZE]; /* receive buffer */


    /* create a UDP socket */

    if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
        perror("cannot create socket\n");
        return 0;
    }

    /* bind the socket to any valid IP address and a specific port */

    memset((char *)&myaddr, 0, sizeof(myaddr));
    myaddr.sin_family = AF_INET;
    myaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    myaddr.sin_port = htons(SERVICE_PORT);

    if (bind(fd, (struct sockaddr *)&myaddr, sizeof(myaddr)) < 0) {
        perror("bind failed");
        return 0;
    }

    /* now loop, receiving data and printing what we received */

    printf("waiting on port %d\n", SERVICE_PORT);
        printf("%s \n \n", "We recieve 10 packets just to confirm the communication");


    recvlen = recvfrom(fd, buf, BUFSIZE, 0, (struct sockaddr *)&remaddr, &addrlen);
        if (recvlen > 0) {
            buf[recvlen] = 0;
            printf("received message: \"%u\" (%d bytes)\n", buf, recvlen);
        }
        else
            printf("uh oh - something went wrong!\n");
        sprintf(buf, "ack %d", msgcnt++);
        printf("sending response \"%u\"\n", buf);
        if (sendto(fd, buf, strlen(buf), 0, (struct sockaddr *)&remaddr, addrlen) < 0)
            perror("sendto");

    int temp = recvlen;

    for (;;) {

    recvlen = recvfrom(fd, buf, BUFSIZE, 0, (struct sockaddr *)&remaddr, &addrlen);
    if (recvlen > 0) {
            buf[recvlen] = 0;
            printf("received message: \"%u\" (%d bytes)\n", buf, recvlen);

    }



}
}

Edit: Here is the output when i ran the code two seperate times: trial run and trial run 2

Answer 1

I believe the problem isn't with your networking code but rather with your printf() calls:

        printf("received message: \"%u\" (%d bytes)\n", buf, recvlen);

You are specifying %u to print out the contents of buf , but buf is a char array (not an unsigned integer), so you probably want to be using %s instead.