c memcpy struct by value

Question

Im simply trying to copy one struct to another (copy by value, NOT by reference). Here is fully working code

/* memcpy example */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define SIZE (80*sizeof(char))

typedef struct {
    char* name;
} person;

int main ()
{
  person p1;
  p1.name = (char*) malloc( SIZE );

  person p2;
  p2.name = (char*) malloc( SIZE );

  // set p1
  strcpy(p1.name, "John");

  // copy p1 > p2
  memcpy ( &p2, &p1, SIZE );

  printf ("p1.name: %s (%u)\n", p1.name, &p1.name );
  printf ("p2.name: %s (%u)\n", p2.name, &p2.name );

  // change p1 only
  printf("Changing p1.name\n");
  strcpy(p1.name, "ONLY p1.name Changed");

  // now, why did p2 change?
  printf ("p1.name: %s (%u)\n", p1.name, &p1.name );
  printf ("p2.name: %s (%u)\n", p2.name, &p2.name );

  free(p1.name);
  free(p2.name);

  return 0;
}

Here is a fiddle http://cpp.sh/57skb

That code outputs

p1.name: John (0x791b3cdd6270)
p2.name: John (0x791b3cdd6280)
Changing p1.name
p1.name: ONLY p1.name Changed (0x791b3cdd6270)
p2.name: ONLY p1.name Changed (0x791b3cdd6280)

Expected output would be

p1.name: John (0x791b3cdd6270)
p2.name: John (0x791b3cdd6280)
Changing p1.name
p1.name: ONLY p1.name Changed (0x791b3cdd6270)
p2.name: John (0x791b3cdd6280)

Question: why does p2 change?

Note that doing the same thing without struct works as expected: http://cpp.sh/6qevd

Answer 1

When you make that copy then both structure name member will have the same value so they point to the same memory location. Your code does not show this since you does not print the pointer value properly. Try this to see that they are indeed the same

  printf ("p1.name: %s (%p)\n", p1.name, p1.name );
  printf ("p2.name: %s (%p)\n", p2.name, p2.name );

Output

p1.name: John (0x3ee8d60)
p2.name: John (0x3ee8d60)

p2 does not change after strcpy(p1.name, "ONLY p1.name Changed");. Simply p2.name points to this new string also.