What is a reference-to-pointer?

Question

I recently saw a function that is being declared as:

void func(type* ¶m);

I already know the difference between type* param

Answer 1

Let's compare all three options:

• void func(type* param); // 'param' is a 'type*' variable
• void func(type& param); // 'param' is a reference to a 'type' variable
• void func(type*& param); // 'param' is a reference to a 'type*' variable

---

void func(type* param)
{
    type x;
    ...
    param = &x;
    // Argument 'param' is regarded as a local variable in this function,
    // so setting 'param = ...' will have no effect outside this function
}

Of course, if you do *param = ..., then it will effect the contents of the memory pointed by param. And you can also do param[5] = ... for example, and effect other areas within that memory space.

---

void func(type& param)
{
    type x;
    ...
    param = x;
    // Argument 'param' is regarded as a reference to a variable outside this
    // function, so setting 'param = ...' will effect the referenced variable
}

Here, you will only change the referenced variable itself, so it's safer than declaring the function as void func(type* param), and then pass the address of type param by calling func(¶m).

---

void func(type*& param)
{
    type x;
    ...
    param = &x;
    // Argument 'param' is regarded as a reference to a variable outside this
    // function, so setting 'param = ...' will effect the referenced variable
}

This is similar to declaring the function as void func(type** param), and then pass the address of type* param by calling func(¶m), but again, it is safer for the same reason mentioned above.

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