How can i copy directly a struct which is in pointer array of structs to another in c

Question

I need to directly copy a value from array to array2 which is a pointer array to use pointing organ values. And in this code, i have used memcpy function but it didn't work:

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

struct organ{
    char *name;
};

struct human{
    struct organ *org;

};

void main(void){
    struct human*array = malloc(sizeof(struct human));
    array[0].org = malloc(sizeof(struct organ));
    array[0].org[0].name= malloc(6);

    struct human*array2 = malloc(sizeof(struct human));
    array2[0].org = malloc(sizeof(struct organ));

    strcpy(array[0].org[0].name, "lungs");
    printf("array name: %s\n",array[0].org[0].name);
    memcpy(&array2[0].org[0], &array[0].org[0], sizeof(struct organ));

    free(array[0].org[0].name);
    free(array[0].org);
    free(array);

    printf("array2 name: %s\n",(array2[0].org[0].name));

    free(array2[0].org);
    free(array2);
}

What did i made wrong? How can i fix this problem ?

Answer 1

Here is a simplification of the problem as in your code:

struct organ a, b;
a.name = malloc(6);
strcpy(a.name, "hello");
b = a;
free(a.name);
puts(b.name);

Your code uses memcpy, but memcpy(&b, &a, sizeof b); is practically the same as b = a; so I have used the simpler syntax in my example.

The problem is that there is only one call to malloc. Both a.name and b.name point to the same memory block. You free that block and then try to output its contents.

Perhaps what you want to do is to make b.name have its own memory block. This means you need to call malloc again, the = operator (or the memcpy function) does not call malloc.

For example in my code, change the b = a; line to:

b.name = malloc( strlen(a.name) + 1 );
strcpy(b.name, a.name);

---

In other words, the procedure for a so-called "deep copy" of a struct organ is not the same as the procedure performed by the assignment operator.

I would recommend that you make a function for performing a copy of struct organ that behaves in the way you want; and call that function instead of using the assignment operator or memcpy.

You could also do the same for copying of a struct human.