Thread: Problem with structures and seg fault

I have some code and I keep getting segfaults, I have found out here the error is happening and it happens when I am trying to assign values to a structure. I thought I had done it right but apparently not. Here is my code and I put comments were the error is happening in the fillStruct function.

Code:

#include <stdio.h>
#include <stdbool.h>

struct NODE //list node
{

 char destination;
 struct NODE* next;

};

struct LIST  //linked list
{
 char startingPoint;
 struct NODE* first;

};

void fillStruct(char* fileName, struct LIST map[]);
void printList(struct LIST map[]);
void depthSearch(struct LIST map[]);
void breadth(struct LIST map[]);
void topoSort(struct LIST map[]);
struct NODE* ListIterator(struct NODE* start);



void fillStruct(char* fileName, struct LIST map[]){

char points[60];
FILE* fpIn;
int i=0;
char readIn=' ';
int j=0;
struct NODE* temp;

for(j=0;j<60;j++)
points[j]=' ';

if((fpIn=fopen(fileName,"r"))!=NULL)
do{

readIn=getc(fpIn);
if(readIn!=EOF && readIn>='A')
points[i++]=readIn;

}while(readIn<'A' && readIn!=EOF);

for(j=0;points[j]!=' ';j+=2){

if(map[(int)points[j]-65].startingPoint==' ')
map[(int)points[j]-65].startingPoint=points[j];

temp->destination=points[j+1]; //error happens here
temp->next=NULL;                     // and here

if(map[(int)points[j]-65].first==NULL)
map[(int)points[j]-65].first=temp;
else{
ListIterator(map[(int)points[j]-65].first)->next=temp;
}


}//end for loop



}

any help is greatly appreciated, Thanks.

Code:

struct NODE* temp;

That's a pointer. A pointer which does not point to anything of value...you don't know where it points. Before you use a pointer it MUST point to a valid memory location. You do this either by pointing it at something already present in memory, or by allocating memory with malloc/calloc.

temp doesn't exist, and yet you try to use it. You need to make temp point to actual memory that you own.

Thanks that fixed it