sender..c

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#define PORT 5500
#define BUFFSIZE 100
#define MIN(_x_,_y_)(((_x_)<(_y_) )? (_x_)<img src="images/smilies/frown.gif" border="0" alt="">_y_))
int main (int argc, char* argv){


  FILE* fin;
  int sd; /*socket descriptor*/
  struct sockaddr_in dest;
  char buf[BUFFSIZE];  /*buffer for socket*/
  unsigned long length, file_size, encoded_file_size, chunk_size;

  memset((char *)&dest, 0, sizeof(dest));
  dest.sin_family = PF_INET;
  dest.sin_port = htons(PORT);
  dest.sin_addr.s_addr = inet_addr("10.0.0.201"); /*destination's address*/



   
  if ((sd = socket(PF_INET,SOCK_DGRAM,0))<0) {
  perror("socket creation");
  }
  fin = fopen("/home/dileo/prova.txt","rb");
  if (fin != NULL){
      fseek(fin,0, SEEK_END);
      file_size = ftell(fin);
      fseek(fin,0, SEEK_SET);
      encoded_file_size = htonl(file_size); /*send dim file*/
       if(sendto(sd, &encoded_file_size, sizeof(encoded_file_size), 0, (struct sockaddr*)&dest, sizeof(dest))<0){ <-here I've                   problem 
       perror("send to error");
       }
       for (length=0; length < file_size; length += chunk_size ){
           chunk_size = MIN(BUFFSIZE, file_size-length);
           fread(buf, chunk_size,1, fin);  /*Check*/
           if (chunk_size != sendto(sd, buf, chunk_size,0,(struct sockaddr*)&dest, sizeof(dest))) <--here Ive problem
              perror("Unable to send data");
       }
    fclose(fin);
    }else{
    printf("Unable to open file");
    }
close(sd);   
}

RECEIVER.c

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#define BUFSIZE 5000
#define DEBUG 1
#define PORT 5500 /*receiver's port*/
#define MIN(_x_,_y_)(((_x_)<(_y_) )? (_x_)<img src="images/smilies/frown.gif" border="0" alt="">_y_))

int main (int argc, char** argv){

  int sd, sfamily, stype, sprotocol;
  struct sockaddr_in receiver, their_addr;
  socklen_t their_addr_len;
  unsigned long file_size;

    memset((char *)&receiver, 0, sizeof(receiver)); /*clean */     
    receiver.sin_family = PF_INET;
    receiver.sin_port = htons(PORT);
    receiver.sin_addr.s_addr = INADDR_ANY;
    
    if ((sd = socket(PF_INET, SOCK_DGRAM, 0))<0)
       perror("socket creation error");
    if (bind(sd, (struct sockaddr*)& receiver, sizeof(receiver))){
    perror("bind error");
    exit(1);
    }

    if (recvfrom(sd,&file_size, sizeof(unsigned long),0, (struct sockaddr*)&their_addr, their_addr_len)<0){
         perror("receive error");
    }
    printf("received packet from %s\n ", inet_ntoa(their_addr.sin_addr));
    printf("packet contains \"%i\"\n",ntohl(file_size));        
    
   FILE *fout = fopen("/home/pippo.txt","wb");
   char buffer[BUFSIZE];
   unsigned long length, chunk_size;
       for (length = 0; length < file_size; length += chunk_size){
#ifdef DEBUG        
        printf("length %i\n", length);
#endif        
    chunk_size = recvfrom (sd, &buffer, MIN(BUFSIZE, file_size-length),0,NULL, NULL);
#ifdef DEBUG
      printf("chunk_size %i\n", chunk_size);
#endif     
    if (!chunk_size){
        printf("connection unexpdeately terminated");
        close(sd);
        }
        
    fwrite(buffer, chunk_size,1, fout); /*<--questa fwrite è reposnsabile segment fault */
        }        
    
fclose(fout);   
close(sd);

return 0;

}