Question

I get the SIGSEGV – Segmentation Fault on the run-time for the code below when the function (log_msg_send) is called. I read that it is about memory violation but I could not find the reason. I would appreciate for the any suggestions/help.

 #define  MAXSTRINGLENGTH 128
#define BUFSIZE 512

void log_msg_send(char *message, char *next_hop);

struct routing {
        int hop_distance;
        char sender_ID[16]; 
};

struct routing user_list[40]  =  { [0]={0,0,0,0}};


int main(int argc,char *argv[]){
    strcpy(user_list[0].sender_ID,"192.168.001.102");
    char message[1000];
    strcpy(message,"123456123456");
     log_msg_send(message, user_list[0].sender_ID);

    return 0;
}

void log_msg_send(char *message, char *next_hop){
    char *SRV_IP;
    strcpy(SRV_IP,  next_hop);

    if (sizeof(SRV_IP) == 16){
         struct sockaddr_in si_other;
         int s, i, slen=sizeof(si_other);
         char buf[60] ;
         strcpy(buf, message);

        if ((s=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))==-1){
          fprintf(stderr, "socket() failed \n");
          exit(1);
        }

        memset((char *) &si_other, 0, sizeof(si_other));
        si_other.sin_family = AF_INET;
        si_other.sin_port = htons(33333);
        if (inet_aton(SRV_IP, &si_other.sin_addr) == 0) {
          fprintf(stderr, "inet_aton() failed \n");
          exit(1);
        }

          if (sendto(s, buf, BUFSIZE, 0,(struct sockaddr *) &si_other, slen)==-1){
          fprintf(stderr, "sendto() failed \n");
          exit(1);
        }

        close(s);
    }
}

PS. For the people who have the SIGSEGV problem. Most common reasons for SIGSEV problem:
– attempting to execute a program that does not compile correctly. Note that most compilers will not output a binary given a compile-time error.
– a buffer overflow.
– using uninitialized pointers.
– dereferencing NULL pointers.
– attempting to access memory the program does not own.
– attempting to alter memory the program does not own (storage violation).
– exceeding the allowable stack size (possibly due to runaway recursion or an infinite loop)

Answer 1

You don’t allocate memory for SRV_IP

char *SRV_IP;
strcpy(SRV_IP,  next_hop);

so the strcpy tries to access invalid memory.

char *SRV_IP = malloc(strlen(next_hop)+1);
if (!SRV_IP) exit(1);
strcpy(SRV_IP,  next_hop);

Then you check

if (sizeof(SRV_IP) == 16){

but SRV_IP is a char*, so its size is whatever size char pointers have, usually 8 or 4 bytes. You probably meant the length, so would have to use strlen.