initialize variables in structure in an array

Question

I created array of structs and I created them in the function config_course_list with a file that contains courses information. I tested variables at the of the function and it is correct. However when I call this function in main, the *courses has size 1, contains only one struct. Which I can print courses[0].code and courses[0].description, but fail to print courses[1].code and description.

What should I do to make it work?

config_course_list:

int config_course_list(Course **courselist_ptr, char *config_filename) {
    FILE *f;
    char buff[INPUT_BUFFER_SIZE];
    f = fopen(config_filename, "r");
    if (f == NULL)
    {
        perror("file");
    }

    fgets(buff,INPUT_BUFFER_SIZE+1,f);
    int size = atoi(buff);

    *courselist_ptr = (Course *)malloc(size * sizeof(Course));
    for (int i = 0; i < size; ++i)
    {
        courselist_ptr[i] = malloc(sizeof(Course));
    }

    int index = 0;
    char *token[size];
    for (int i = 0; i < size; ++i) 
    {
        token[i] = malloc(sizeof(char)*INPUT_BUFFER_SIZE);
    }

    while (fgets(buff,INPUT_BUFFER_SIZE+1, f) != NULL)
    {
        strcpy(courselist_ptr[index]->code, strtok(buff, " "));
        strcpy(token[index],strtok(NULL, "\n"));
        courselist_ptr[index]->description=token[index];
        index ++;
    }

    return size;
}

main:

Course *courses; 
int num_courses = config_course_list(&courses, argv[1]);
printf("%s\n", courses[1].code);

struct course:

struct course{
    char code[7];
    char *description;
};

If fopen() fails, this code prints an error message, then continues as if everything is OK.... You seem to be missing a typedef for Course. — ad absurdum
– ad absurdum, Commented Oct 12, 2018 at 4:40
Please take the tour, read this: How to Ask and provide a minimal reproducible example. — Jabberwocky
– Jabberwocky, Commented Oct 12, 2018 at 4:46
All int better were size_t. sizeof (char) equals 1 by definition. No need to cast void-pointers, like malloc()'s result. — alk
– alk, Commented Oct 12, 2018 at 11:58

rafix07 · Accepted Answer · 2018-10-12 06:39:28Z

Delete these lines:

 for (int i = 0; i < size; ++i)
    {
        courselist_ptr[i] = malloc(sizeof(Course));
    }

what is the purpose of above loop ? It looks like you want to create 2D array ... not this way.

Your aim is to create 1D array and you do it by

*courselist_ptr = (Course *)malloc(size * sizeof(Course));

and it is enough, the array was created now you can fill it by some data.

When you created 1D array, and p points to the first element of this array you have two ways to access i-th element:

p[i]

or

*(p + i)
  ^    - p is pointer to first element of array

In your case p is *courselist_ptr so if you want to read/write code member you can use:

(*courselist_ptr)[i].code 
(*courselist_ptr + i)->code
(*(*courselist_ptr + i)).code

so you have to replace courselist_ptr[index]->code by (*courselist_ptr)[index].code and courselist_ptr[index]->description by (*courselist_ptr)[index].description.

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