I have an assignment and have run into somewhat of a snag. The following code is supposed to take input from a file, read it into a struct that I have defined, and do so without any limit to the number of input lines. However, it segfaults at line 24:
1 #include <stdio.h>
2 #include <stdlib.h>
3 #include <string.h>
4
5 typedef struct __student {
6 int ID;
7 char fname[33];
8 char lname[33];
9 float grade;
10 } student;
11
12 void partA(FILE *fp) {
13
14 int i, r;
15 i = r = 0;
16 int N = 1000;
17 student **S;
18
19 S = (student **)malloc(sizeof(student *) * N);
20
21
22 while(!feof(fp)){
23 fscanf(fp, "%d %[^,], %s %f", &S[i]->ID, S[i]->lname, S[i]->fname, &S[i]->grade ); // segfault occurs on this line
24 printf("%d %s %s %f\n", S[i]->ID, S[i]->fname, S[i]->lname, S[i]->grade);
25 i++;
26 printf("Something's happening, at least");
27 if(i == N){
28 N *= 2;
29 S = (student **)realloc(S, sizeof(student) * N);
30 if(S == NULL) {
31 printf("Memory reallocation failed; Fatal error.");
32 break;
33 }
34 }
35 }
36 }
I tested the code before, although at that point I was using static arrays and wanted to change to a dynamic size. However, even gdb with offers very little help besides the line number. Do I need to individually malloc each student struct, or am I missing something entirely different here?
EDIT: It seems the code works when I allocate memory to each student in the while loop through:
S[i] = (student *)malloc(sizeof(student));
So that seems to have fixed the issue. I'll run some tests to make sure.
On line 19 you are allocating enough space for N student pointers but not allocating space for the student structs them selves. You would need to do something like:
for( int i = 0; i < N; i++) {
S[i] = malloc(sizeof(struct __student));
}