How to modify pointer to structure inside void function

Question

I tried to google my problem many times but never found an answer that fits my problem. I have to modify a pointer to a structure inside a function(fill it with data), and then use that pointer as an argument to another functions. I have a text file that has multiple reports in it and I am supposed to count the reports and fill all the data to a pointer to a structure. Which isnt a problem, I allocated memory without a problem, got through the file without a problem and also filled the pointer. But I can't figure out how to use the filled pointer outside of the function.

struct report{
  char name[50];
  int id_number;
}

void function1(struct report **ptr){
  //do stuff like count the number of reports in file
  //and allocate memmory for pointer to structure
  //and fill the pointer to structure with data
}
int main() {
  struct report *pointer;
  function(pointer);
  //now I expect variable 'pointer' to be filled and ready to use by another functions
  return 0;
}

Can you please suggest some solutions please? Thank you for your time and help.

Do you allocate the memory in function1 on the heap?

H.cohen
– H.cohen

2018-10-29 09:33:04 +00:00
Commented Oct 29, 2018 at 9:33 — H.cohen
– H.cohen, Commented Oct 29, 2018 at 9:33

Ivan Velichko · Accepted Answer · 2018-10-29 09:34:26Z

2

Please have a look at the example:

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

struct report{
  char name[50];
  int id_number;
};

void foo(struct report **ptr){
  *ptr = malloc(sizeof(struct report));  // allocate memory
  (*ptr)->id_number = 42;  // fill the allocated memory
}

int main() {
  struct report *pointer;
  foo(&pointer);  // important part - pass to the foo() pointer to the pointer.

  printf("%d\n", pointer->id_number);

  free(pointer);  // do not forget to free the memory.
  return 0;
}

answered Oct 29, 2018 at 9:34

Ivan Velichko

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