Question

I (think I) understand that you can only retrieve the size of an array (using sizeof) if it is declared at compile time on the stack, e.g.

int my_array[] = {1,2,3};
sizeof(my_array) == 3;

As soon as you start using pointers you lose this length information.

e.g. if you pass a pointer to int as a function parameter to get an int array into a function you can no longer use sizeof() in this way, it will just return the number of bytes used to store a pointer.

Clearly, it is vital to know how long your arrays are.

So which of the following options should I use when passing arrays around?

1. Pass a pointer and an accompanying length parameter

   int my_func(int *my_array, size_t len_my_array)

2. Create my own vector struct

   struct vector {
      int *my_array;
      size_t len;
   }
   
   int my_func(struct vector *my_vector)
   

3. Use someone elses vector implementation. (Is there a default implementation for C as there is for C++?)

4. Another approach which I’ve missed?

(I’m currently using the 1st option but its a bit unwieldy and I’m keen to know if this is considered poor programming practice)

Answer 1

The standard way is to utilize the first approach and pass a pointer and a size especially if you want your code to be reused by others.