Dereferencing Pointers

Reading Through a Pointer

Placing * before a pointer variable reads the value it points to. This is how code that only has a pointer can still get at the underlying data.

Example: Reading Through a Pointer

package main

import "fmt"

func main() {
	age := 30
	p := &age
	fmt.Println("age via pointer:", *p)
}

Writing Through a Pointer

Assigning to *p, rather than just reading it, changes the original value the pointer refers to -- this is how a function can modify a caller's variable through a pointer parameter.

Example: Writing Through a Pointer

package main

import "fmt"

func main() {
	age := 30
	p := &age
	*p = 31
	fmt.Println("age is now:", age)
}

Nil Pointer Dereferencing Panics

A pointer that hasn't been assigned an address (its zero value) is nil, and attempting to dereference it crashes the program with a runtime panic -- there is no value at address zero to read or write.

Note: Always check 'if p != nil' before dereferencing a pointer that might not have been set.

Example: Nil Pointer Dereferencing Panics

package main

import "fmt"

func safeRead(p *int) {
	if p == nil {
		fmt.Println("pointer is nil, nothing to read")
		return
	}
	fmt.Println("value:", *p)
}

func main() {
	var p *int
	safeRead(p)
	x := 5
	safeRead(&x)
}

Automatic Dereferencing for Struct Fields

When accessing a struct field through a pointer, Go automatically dereferences it for you -- p.Field is shorthand for (*p).Field, so you rarely need to write the explicit dereference for field access.

Example: Automatic Dereferencing for Struct Fields

package main

import "fmt"

type Point struct {
	X, Y int
}

func main() {
	p := &Point{X: 1, Y: 2}
	fmt.Println(p.X, p.Y) // shorthand for (*p).X, (*p).Y
}