memcpy vs for loop - What's the proper way to copy an array from a pointer?

Question

I have a function foo(int[] nums) which I understand is essentially equivalent to foo(int* nums). Inside foo I need to copy the contents of the array pointed to by numsinto some int[10] declared within the scope of foo. I understand the following is invalid:

void foo (int[] nums)  {     myGlobalArray = *nums } 

What is the proper way to copy the array? Should I use memcpy like so:

void foo (int[] nums) {     memcpy(&myGlobalArray, nums, 10); } 

or should I use a for loop?

void foo(int[] nums) {     for(int i =0; i < 10; i++)     {         myGlobalArray[i] = nums[i];     } } 

Is there a third option that I'm missing?

Answer 1

Yes, the third option is to use a C++ construct:

std::copy(&nums[0], &nums[10], myGlobalArray); 

With any sane compiler, it:

• should be optimum in the majority of cases (will compile to memcpy() where possible),
• is type-safe,
• gracefully copes when you decide to change the data-type to a non-primitive (i.e. it calls copy constructors, etc.),
• gracefully copes when you decide to change to a container class.

Answer 2

Memcpy will probably be faster, but it's more likely you will make a mistake using it. It may depend on how smart your optimizing compiler is.

Your code is incorrect though. It should be:

memcpy(myGlobalArray, nums, 10 * sizeof(int) );