How does dereferencing of a function pointer happen?

In C or C++, calling the function pointed to by a function pointer is achieved by using the function pointer directly. Function pointers can be viewed as pointers to functions, which store the address of a function and allow calling that function through the pointer.

Function Pointer Definition

First, the syntax for defining a function pointer is:

c
return_type (*pointer_variable_name)(parameter_type_list);

For example, if you have a function returning int and accepting two int parameters, you can define a pointer to such a function as:

c
int (*funcPtr)(int, int);

How to Use a Function Pointer

Assume we have a function add:

c
int add(int x, int y) {
    return x + y;
}

We can assign the address of this function to the previously defined function pointer:

c
funcPtr = add;

Calling the Function Pointed to by a Function Pointer

Calling the function pointed to by a function pointer can be done directly using function call syntax, like this:

c
int result = funcPtr(3, 4);

Here, funcPtr(3, 4) effectively calls add(3, 4), returning a value of 7.

Deep Dive: Syntax of Dereferencing

Actually, in C or C++, when calling a function via a function pointer, explicit dereferencing is not necessary. As mentioned above, directly using funcPtr(3, 4) suffices to call the function. However, for better conceptual understanding, you can explicitly dereference it using the following syntax:

c
int result = (*funcPtr)(3, 4);

Here, (*funcPtr) explicitly dereferences the function pointer. Although this is typically optional in function pointer usage, as the function name itself represents the address of the function, funcPtr and (*funcPtr) are equivalent during function calls.

Summary

Through the above examples, we can see the definition, initialization, and process of calling a function via a function pointer. Function pointers provide a flexible way to call functions, especially useful when dynamically selecting functions based on conditions, such as in callback functions or event handlers.