Struct and pointer

Learn struct pointers and dot access.

Structs and pointers

When accessing fields through a struct pointer you don't need to write (*p).Ad; Go does it automatically: p.Ad.

k := &Kitap{Title: "Dune", Sayfa: 412}
k.Sayfa = 500           // same as (*k).Sayfa = 500
fmt.Println(k.Sayfa)    // 500

Pointers are used to change a struct in a function or to pass a large struct without copying it.

Changing it in a function

If a struct is passed by value the function works on a copy; to keep the change, pass a pointer:

func zamYap(c *Calisan, oran float64) {
    c.Maas *= 1 + oran
}

c := Calisan{Ad: "Ada", Maas: 1000}
zamYap(&c, 0.1)
fmt.Println(c.Maas)  // 1100

Exercise Give a raise

Write the Calisan struct (Ad string, Maas float64) and the zamYap(c *Calisan, oran float64) function. Give a 0.1 raise to an employee with Maas: 1000 and print the salary.

Show example solution

package main

import "fmt"

type Calisan struct {
    Ad   string
    Maas float64
}

func zamYap(c *Calisan, oran float64) {
    c.Maas *= 1 + oran
}

func main() {
    c := Calisan{Ad: "Ada", Maas: 1000}
    zamYap(&c, 0.1)
    fmt.Println(c.Maas)
}

Test yourself

What is the correct way to access a field through a struct pointer?
- p.Ad
- p->Ad
- *p.Ad
- p::Ad
Show answer

p.Ad — Go dereferences the pointer automatically with the dot operator; -> and :: don't exist in Go, and *p.Ad is read as *(p.Ad).

Struct pointer

func zamYap(c ____Calisan, oran float64) {
    c.Maas *= 1 + oran
}

Show answer

func zamYap(c *Calisan, oran float64) {
    c.Maas *= 1 + oran
}

Code and effect

p.Ad (p *Kitap)

Automatic dereference
f(k) (value)

The copy changes
f(&k) (pointer)

The original changes
&Kitap{...}

Creates a pointer

Next lesson: Summary - Struct

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