help with seg fault

hi all.

Can someone explain why U get a segmentation fault in the following block of code

Code:

---

int setup(char *hostname, int ttl, SOCKET *icmpSock, SOCKADDR_IN *dest)
{
    HOSTENT *hp;
    unsigned int addr;
    int sockRet;
   
    // create socket
    *icmpSock = WSASocket(AF_INET, SOCK_RAW, IPPROTO_ICMP, NULL, 0, 0);
    if (*icmpSock == INVALID_SOCKET) {
      printf("Could not create socket : %d.\n", WSAGetLastError());
      return -1;
    }
   
    // setup for TTL
    sockRet = setsockopt(*icmpSock, IPPROTO_IP, IP_TTL, (const char *)&ttl, sizeof(ttl));
    if (sockRet == SOCKET_ERROR) {
      printf("ttl setsockopt failed : %d. \n", WSAGetLastError());
      return -1;
    }
   
    memset(&dest, 0, sizeof(*dest));
    addr = inet_addr(hostname);
    if (addr == INADDR_NONE) {
      hp = gethostbyname(hostname);
      if (hp != 0) {
          //memcpy(&dest->sin_addr, hp->h_addr, hp->h_length);
          dest->sin_addr = *((struct in_addr *)hp->h_addr);
          dest->sin_family = hp->h_addrtype;
      } else {
          printf("unknown hostname || failed to resolve\n");
          return -1;
      }
    } else {
        dest->sin_addr.s_addr = addr;
        dest->sin_family = AF_INET;
    }
   
    return 0;
}

---

The error is coming from the line dest->sin_addr = *((struct in_addr *)hp->h_addr);
I get the same error if I try to use memcpy as above it.

dest is a pointer to an empty structure.

Thanks.

> memset(&dest, 0, sizeof(*dest));
Remove the &
You just made your pointer a NULL pointer, and hosed a bunch of memory following it as well.

Thanks Salem.

When you get a sec, can you just quickly explain why the pointer was set null and what happened to the memory.

Thanks.

Quote:

---

2.14.6 memset

Declaration:

Code:

---

void *memset(void *str, int c, size_t n);

---

Copies the character c (an unsigned char) to the first n characters of the string pointed to by the argument str.

The argument str is returned.

---

memset(dest, 0, sizeof(*dest));
The second argument is what is being filled into dest

I was using this page as a learning reference http://tangentsoft.net/wskfaq/examples/rawping.html

In their function setup_for_ping they set the address of dest to 0 as I did initially. (I see why thats wrong now. Thanks sand_man.)

This is quite a popular paper and if theirs was wrong, I would have though someone would have picked up on it.

So assuming theirs is right, what makes mine different than theirs?

Perhaps because yours is an inaccurate translation of the C++ code (on that page) to the C code (you posted)