Golang Pointers Comprehension

Introduction

This lab will test your understanding of pointers in Golang. Pointers are used to pass references to values and records within your program.

Skills Graph

Pointers

The problem is to understand how pointers work in contrast to values with two functions: zeroval and zeroptr. zeroval has an int parameter, so arguments will be passed to it by value. zeroval will get a copy of ival distinct from the one in the calling function. zeroptr in contrast has an *int parameter, meaning that it takes an int pointer. The *iptr code in the function body then dereferences the pointer from its memory address to the current value at that address. Assigning a value to a dereferenced pointer changes the value at the referenced address.

• You should have a basic understanding of Golang.
• You should know how to define and use functions in Golang.
• You should know how to use pointers in Golang.

## `zeroval` doesn't change the `i` in `main`, but
## `zeroptr` does because it has a reference to
## the memory address for that variable.
$ go run pointers.go
initial: 1
zeroval: 1
zeroptr: 0
pointer: 0x42131100

There is the full code below:

// Go supports <em><a href="https://en.wikipedia.org/wiki/Pointer_(computer_programming)">pointers</a></em>,
// allowing you to pass references to values and records
// within your program.

package main

import "fmt"

// We'll show how pointers work in contrast to values with
// 2 functions: `zeroval` and `zeroptr`. `zeroval` has an
// `int` parameter, so arguments will be passed to it by
// value. `zeroval` will get a copy of `ival` distinct
// from the one in the calling function.
func zeroval(ival int) {
	ival = 0
}

// `zeroptr` in contrast has an `*int` parameter, meaning
// that it takes an `int` pointer. The `*iptr` code in the
// function body then _dereferences_ the pointer from its
// memory address to the current value at that address.
// Assigning a value to a dereferenced pointer changes the
// value at the referenced address.
func zeroptr(iptr *int) {
	*iptr = 0
}

func main() {
	i := 1
	fmt.Println("initial:", i)

	zeroval(i)
	fmt.Println("zeroval:", i)

	// The `&i` syntax gives the memory address of `i`,
	// i.e. a pointer to `i`.
	zeroptr(&i)
	fmt.Println("zeroptr:", i)

	// Pointers can be printed too.
	fmt.Println("pointer:", &i)
}

Summary

In this lab, you learned how to use pointers in Golang. You also learned the difference between passing values and pointers to functions.