以下两个不同的传递变量方法到函数之间的区别

Question

I have the following struct and two kinds of methods listed below. Which method is better and why?

typedef struct _MY_ST_
{
  int a;
  int b;
} MY_ST;

Method 1:

int func1(MY_ST my_st)
{
  int temp;
  temp = my_st.a + my_st.b;
  return temp;
}

Method 2:

int func2(const MY_ST *const my_st)
{
  int temp;
  temp = my_st->a + my_st->b;
  return temp;
}

Answer 1

With such a small structure (2 integers), you won't see a difference.

In general, though, it usually makes sense to pass a pointer to the structure, since it avoids unnecessary copying. But in this specific case, I'd say just go with whatever you're more comfortable with and makes sense for you.

Also, you don't need the parameter in func2() to be const MY_ST *const my_st . const MY_ST *my_str will suffice, because the pointer is passed by copy, so there is no way that the callee will modify the caller's pointer value.

Answer 2

I would say the second method is better because you only pass a pointer to the memory where your structure is held. In the first method you pass the who structure and the computer will duplicate in memory the structure in the function - a copy of the structure will be made. (but a compiler running optimization may make the two methods equivalent)