Allocating dynamic array of struct on C.

Question

Allocating dynamic array of struct on C. Valgrind found this error: Use of uninitialised value of size 8. The error pops up while trying to access the struct member.

What is the way to avoid that?

void find_rate()
{
  int num_lines = 0;
  FILE * in;
  struct record ** data_array;
  double * distance;
  struct record user_record;

  in = open_file();

  num_lines = count_lines(in);

  allocate_struct_array(data_array, num_lines);

  data_array[0]->community_name[0] = 'h';       // the error is here
  printf("%c\n", data_array[0]->community_name[0]);

  fclose(in);
}

FILE * open_file()
{
  ..... some code to open file
  return f;
}

int count_lines(FILE * f)
{
  .... counting lines in file
  return lines;
}

Here is the way I allocate the array:

void allocate_struct_array(struct record ** array, int length)
{
  int i;

  array = malloc(length * sizeof(struct record *));

  if (!array)
    {
      fprintf(stderr, "Could not allocate the array of struct record *\n");
      exit(1);
    }

  for (i = 0; i < length; i++)
    {
      array[i] = malloc( sizeof(struct record) );

      if (!array[i])
    {
      fprintf(stderr, "Could not allocate array[%d]\n", i);
      exit(1);
    }
    }
}

Answer 1

Since you are passing the address of array to the function allocate_struct_array

You need:

*array = malloc(length * sizeof(struct record *));

And in the calling function you need to declare data_array as:

struct record * data_array;

and pass its address as:

allocate_struct_array(&data_array, num_lines);