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References and Pointers

Pass-By-Reference

In C++, pass-by-reference refers to passing parameters to a function by using references.

It allows the ability to:

  • Modify the value of the function arguments.
  • Avoid making copies of a variable/object for performance reasons.
void swap_num(int &i, int &j) {


  int temp = i;
  i = j;
  j = temp;


}


int main() {


  int a = 100;
  int b = 200;


  swap_num(a, b);


  std::cout << "A is " << a << "\n";
  std::cout << "B is " << b << "\n";


}

const Reference

In C++, pass-by-reference with const can be used for a function where the parameter(s) won’t change inside the function.

This saves the computational cost of making a copy of the argument.

int triple(int const &i) {


  return i * 3;


}

Pointers

In C++, a pointer variable stores the memory address of something else. It is created using the * sign.

int* pointer = &gum;

References

In C++, a reference variable is an alias for another object. It is created using the & sign. Two things to note:

  1. Anything done to the reference also happens to the original.
  2. Aliases cannot be changed to alias something else.
int &sonny = songqiao;

Memory Address

In C++, the memory address is the location in the memory of an object. It can be accessed with the “address of” operator, &.

Given a variable porcupine_count, the memory address can be retrieved by printing out &porcupine_count. It will return something like: 0x7ffd7caa5b54.

std::cout << &porcupine_count << "\n";

Dereference

In C++, a dereference reference operator, *, can be used to obtain the value pointed to by a pointer variable.

int gum = 3;


// * on left side is a pointer
int* pointer = &gum;


// * on right side is a dereference of that pointer
int dereference = *pointer;

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