Clash Royale CLAN TAG

Copying char arr[64] to char arr can cause a segmentation fault?

typedef struct {
int num;
char arr[64];
} A;

typedef struct {
int num;
char arr;
} B;


I declared A* a; and then put some data into it. Now I want to cast it to a B*.

A* a;

B*

A* a;
a->num = 1;
strcpy(a->arr, "Hi");

B* b = (B*)a;


Is this right?
I get a segmentation fault sometimes (not always), and I wonder if this could be the cause of the problem.

I got a segmentation fault even though I didn't try to access to char arr after casting.

char arr

1 Answer
1

This defines a pointer variable

A* a;


There is nothing it is cleanly pointing to, the pointer is non-initialised.

This accesses whatever it is pointing to

a->num = 1;
strcpy(a->arr, "Hi");


Without allocating anything to the pointer beforehand (by e.g. using malloc()) this is asking for segfaults as one possible consequence of the undefined behaviour it invokes.

malloc()

...asking for undefined behaviour

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