如何在C中的Struct中使用memcpy？

Question

I have a struct:

struct points{
int i;
int x;
int y;
};

I made an array of the struct and named it temp. Then I made another and named it pt. Suppose I put some contents to temp. How can I copy the elements of temp to pt?

Here's my code of memcpy and the compiler says it's segmentation fault. Help please.

#define MAX_POINTS 400
struct points temp[MAX_POINTS];
/* Some code to input elements to array temp */
struct points pt[i]; /* array of struct with i elements*/
memcpy(&pt, &temp, sizeof (temp));

Answer 1

You have to be careful to only copy the size of the smaller of the two, here I suppose that i < MAX_POINTS

memcpy(pt, temp, sizeof pt);

Also as others already said the & are not correct. You need a pointer to the first element, that is &pt[0] for example, or just pt as the array decays to &pt[0] in that context.

Note that your allocation of pt is a variable length array if i is a variable. This can be dangerous and lead to a stack overflow if i is getting too large. So if you plan to use large arrays here, better use malloc :

struct points* pt = malloc(sizeof(struct points[i]));
memcpy(pt, temp, sizeof(struct points[i]);

Unfortunately then, you can't use sizeof pt for the memcpy .