how to copy struct data in C language?

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!

IMO, if you're wanting to deep copy like that, something you're doing is *very wrong*. You might want to think about: What do you want to do with the `parent`'s `parent`? You want that copied too? And what do you want done when the array of `nodes` is copied? You want their `nodes` arrays to be copied too? — ArjunShankar, Aug 06 '12 at 08:31
Even a single day hasn't passed since you asked the exact same question. — , Aug 06 '12 at 08:40
possible duplicate of [How to duplicate a struct with char* and point on it?](http://stackoverflow.com/questions/11816406/how-to-duplicate-a-struct-with-char-and-point-on-it) — , Aug 06 '12 at 08:40

Razvan · Accepted Answer · 2012-08-06T08:49:54.590

2

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.

edited Aug 06 '12 at 08:49

answered Aug 06 '12 at 08:38

Razvan

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While you're right about `calloc` not making sense here, the reason you state (used for arrays) might not be very accurate. `calloc` initializes allocated memory to 0s (to me, this is the bigger difference between `malloc` and `calloc`). – ArjunShankar Aug 06 '12 at 08:50
Ok, got your point. void * calloc ( size_t num, size_t size ); Allocates a block of memory for an array of num elements, each of them size bytes long, and initializes all its bits to zero So, i think it's primary purpose is to allocate arrays. – Razvan Aug 06 '12 at 08:52
2

Erm, if you insist, then sure. (But have a look at [this](http://stackoverflow.com/q/1538420/274261). Most people seem to care more about the 0's done by `calloc`.) – ArjunShankar Aug 06 '12 at 08:57

how to copy struct data in C language?

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