How do I create a dynamic array of struct pointers?

Question

I need to read in some data from a csv file, and store each component into a struct.

The csv file has the following headers: name, last name, phone number, age

The csv file has an unknown number of records, and I want to create a dynamic array of pointers to structs to store this data.

I started with this:

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

int main(int argc, char **argv){
    typedef struct{
    char** name; 
    char** last_name; 
    int * number;
    int* age}person_t;

    person_t **storage;


}

But now I am absolutely stuck and have no idea how to proceed. Please help!

Does this answer your question? Allocating memory for a Structure in C — Mark Benningfield
– Mark Benningfield, Commented Aug 20, 2021 at 15:43
Not necessarily the question you asked about, but: you've got a bunch of unnecessary extra pointer levels in your person_t type. You want int age, not int *age. You might want char *name and char *last_name, but those will require allocation, too, so for a start maybe go with char name[10] and char last_name[20]. Not sure about the phone number. — Steve Summit
– Steve Summit, Commented Aug 20, 2021 at 15:50
You need to decide whether you want an array of pointers to your structures, or just an array of your structures. The simpler array of structures will be easier at first, which will be person_t *storage. — Steve Summit
– Steve Summit, Commented Aug 20, 2021 at 15:54

Jabberwocky · Accepted Answer · 2021-08-20 16:24:53Z

0

You probably want something like this:

typedef struct{
  char name[20];        // can store names of maximum length 19
  char last_name[20];   // can store last names of maximum length 19
  int number;
  int age
} person_t;


int main(int argc, char **argv){
  person_t **storage;
  ...
  // allocate an array of nbOfElements pointers to person_t
  storage = malloc(nbOfElements * sizeof(person_t*));

  for (int i = 0; i < nbOfElements; i++)
  {
     ...
     ... read one CSV line 
     ...
     // allocate memory for one person_t and store the pointer
     storage[i] = malloc(sizeof(person_t));
   
     // fill the structure
     strcpy(storage[i]->name, ...);
     strcpy(storage[i]->last_name, ...);
     storage[i]->number = ...
     storage[i]->age = ...;
  }        
}

This is not complete code, just an outline of what you could do. Also there are no error checks for malloc for brevity.

answered Aug 20, 2021 at 16:24

Jabberwocky

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1 Comment

Steve Summit Over a year ago

And the OP said "The csv file has an unknown number of records", so pretty soon there'll be an opportunity to learn about realloc.

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