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segmentation fault while sending UDP packets!

The following piece of code is suppose to send a UDP packet.
but inside function udpsocketinit , i get a segmentation fault and i can not understand why!!
please help me

Code:

#include <arpa/inet.h>

#include <netinet/in.h>

#include <stdio.h>

#include <sys/types.h>

#include <sys/socket.h>

#include <unistd.h>

    

#define BUFLEN 512

#define NPACK 10

#define PORT 9930

#define SRV_IP "127.0.0.1"  

void udpsocketinit (struct sockaddr_in *sok)

{

        struct in_addr *xyz;

//        memset((char *) sok, 0, sizeof(sok));

        sok->sin_family = AF_INET;

        sok->sin_port = htons(PORT);

        xyz=&(*sok).sin_addr;

        if (inet_aton(SRV_IP, xyz)==0)

        {

          printf("the ip address is wrong\n");

        }



} 



    

int main(void)

 {

        struct sockaddr_in *si_other;

        int s, i, slen=sizeof(si_other);

        char buf[BUFLEN];

    

        if ((s=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))==-1)

            printf("socket is not initialised\n");

        udpsocketinit(si_other);



    

        for (i=0; i<NPACK; i++)

        {

          printf("Sending packet %d\n", i);

          sprintf(buf, "This is packet %d\n", i);

          if (sendto(s, buf, BUFLEN, 0, si_other, slen)==-1)

                printf("socket bind failed!\n");

        }

    

        close(s);

        return 0;

}

Try this:

Code:

int udpsocketinit(struct sockaddr_in *sok)

{

    struct in_addr xyz;



    if (inet_aton(SRV_IP, &xyz) == 0)

    {

        printf("the ip address is wrong\n");

        return -1;

    }



    sok->sin_addr = xyz;

    sok->sin_family = AF_INET;

    sok->sin_port = htons(PORT);

    return 0;

}



int main(void)

{

    struct sockaddr_in si_other;

    int s, i, slen = sizeof(si_other);

    char buf[BUFLEN];

    int ret;



    ret = -1;



    if ((s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1)

    {

        printf("socket is not initialised\n");

        goto socket_err;

    }



    if (udpsocketinit(si_other))

    {

        goto init_err;

    }



    for (i = 0; i < NPACK; i++)

    {

        printf("Sending packet %d\n", i);

        sprintf(buf, "This is packet %d\n", i);

        if (sendto(s, buf, BUFLEN, 0, &si_other, slen) == -1)

        {

            printf("socket bind failed!\n");

            goto send_err;

        }

    }



    ret = 0;

    goto done;



send_err:

init_err:

done:

    close(s);



socket_err:

    return(ret);

}

Quote:

Originally Posted by bizoo (Post 3609340)

struct sockaddr_in *si_other;

That just defines a pointer to that structure type. It does not make the pointer point at anything.

Quote:

int s, i, slen=sizeof(si_other);

That sets slen to the size of a pointer. Is that what you intend, or did you intend slen to be the size of the type of object that the pointer would point to?

Quote:

udpsocketinit(si_other);

You use that pointer as if it is the address of an actual object, but it is just an uninitialized pointer.

In main you declare a pointer to struct sockaddr_in (si_other) that is never initialized (so pointing to somewhere in memory). Next you try (in udpsockinit) to assign a value to an element of that struct so writing to memory that more than likely is not 'yours'.

bizoo,

I made some changes to my earlier post. They should fix your problems. However I have not tested them.

Good luck.

thanks all esp. David
Yup the problem indeed was initializing a pointer but not directing it to some struct