Assigning values to array of struct pointers

Question

I am trying to make an Array of struct pointers so I can terminate the end of the array with null and be able to run through the array of structs.

I originally got an array of structs working but when changing the array of structs into an array of struct pointers I get a segmentation fault when trying to assign or access values of the structs by dereferencing.

I like to know what I am doing wrong.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct s{
    int a;
    char *b;
    int c;
    int d;
}s;

s** readStruct(){
    FILE *f = fopen("file.csv", "r");
    if(!f){
        printf("Can't open file\n");
        exit(1);
    }

    //An array of struct pointers of size 50
    s **x = (s **)malloc(50 * sizeof(s *));
    char str[60];
    int i = 0;

    //Loop through each line of the file while !EOF
    //copy each line to string for tokenizing
    while(fgets(str, 60, f)){

        char *tok = strtok(str, ",/n");
        // segmentation fault happens here:
        x[i]->a = atoi(tok);
        // also happens here too:
        printf("%d\n", x[i]->a);

        tok = strtok(NULL, tok);
        // segmentation fault would result here:
        strcpy(x[i]->b, tok);

        tok = strtok(NULL, ",\n");
        // and here:
        x[i]->c = atoi(tok);

        tok = strtok(NULL, ",\n");
        // and here:
        x[i]->d = atoi(tok);

        i++;
    }

    return x;
}

int void main(){

    s **x = readStruct();

    for(int i = 0; (x + i) < NULL; i++){
        printf("%d\n", x[idx]->a);
        printf("%s\n", x[idx]->b);
        printf("%d\n", x[idx]->c);
        printf("%d\n", x[idx]->d);
        printf("\n");
    }


    return 0;
}

This worked, makes sense too.

TheWinterSnow
– TheWinterSnow

2015-11-06 22:47:31 +00:00
Commented Nov 6, 2015 at 22:47 — TheWinterSnow
– TheWinterSnow, Commented Nov 6, 2015 at 22:47

Community · Accepted Answer · 2017-05-23 10:27:16Z

1

You allocated the space for the array, but not for each individual struct that the pointers in the array point to:

while(fgets(str, 60, f)){

    char *tok = strtok(str, ",/n");

    a[i] = malloc( sizeof( s ) );
    //...

Other notes:

In C, you should not cast the result of malloc().
Since you are reusing the delimiter string, it would be good to store that in a variable (const char* delim = ",\n") instead of retyping the same sequence. It helps to prevent errors, like typing ",/n", when you mean ",\n" which you did.

edited May 23, 2017 at 10:27

CommunityBot

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answered Nov 6, 2015 at 22:38

clcto

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1 Comment

TheWinterSnow Over a year ago

Awesome, that did that job.

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