How do I (deep) copy an array in C?

Question

Refering to http://www.devx.com/tips/Tip/13291, it says that I can use memcpy with the size to copy determined by sizeof(), however, isn't the array pointing to a pointer?

Other than iterating through the array, how can I use memcpy to deep copy an array?

Thanks!

Answer 1

In the linked example int weekly_hours[5][5]; allocates space for 25 integers. There is no further indirection, so you can safely use memcpy to duplicate it's values.

Answer 2

A multi-dimensional array is contiguously allocated. An array of pointers (of pointers...) is a different thing (and each sub-pointer should be allocated/copied/freed on its own).

Do not be confused by the fact that an unidimensional array and a single pointer can be used interchangeably in most situations, because they are not technically the same.

Answer 3

To hopefully clear up some of the confusion:

• An array is a chunk of allocated, adjacent memory cells.
• An array variable name can transform ("decay") into a pointer to the first element of the array, but not the other way around. This is done implicitly each time you use the array variable name in pointer arithmetics.
• You can use the sizeof() operator on the variable name of any statically alloced array, to get the number of bytes in the array. If sizeof() is used on a statically allocated, multi-dimensional array, the same applies.
• If you use the sizeof() operator on a pointer, you will get the size of a pointer (i.e. 4 bytes on a 32-bit machine).