Question

I’m still having trouble understanding how to copy structs that include char* fields\other struct fields:

typedef struct node{
   int id;
   struct node* parent
   char * nodeName;
   struct node* nodes[100];
 }NODE,*pNODE;

I want to use this function : pNODE copyNode(pNODE oldNode)
1. i know that first I should do allocation for the new pointer data , and do the followong:

pNODE newNode = (pNODE)calloc(1,sizeof(NODE));
newNode.id=oldNode.id
//for the string that I want to copy I should allocate and use strcpy - in order not to point at the same string

but now I’m lost regarding the parent node, how do I copy it ? if I just do : newNode.parent=oldNode.parent
I point at the same parent object, and if I change it’s Id for example – it will change both the id of newNode and oldNode. how can I copy it?? without pointing at the same one?
and how can i copy the pointer array??

thank you!

Answer 1

Take a look at the memcopy function:

memcpy(oldNode.parent, newNode.parent, sizeof(node)).

Of course, you first need to allocate memory for the newNode’s parent, using malloc (calloc doesn’t make sense in this context – it’s used for arrays)

newNode.parent = (NODE*)malloc(sizeof(NODE))

If you want to do a deep-copy (i.e. don’t reuse referenced objects), you should go through the newNode struct and allocate memory for each pointer contained in the struct and then apply memcopy.