Pointer to a struct in Go (Golang) - Welcome To Golang By Example

In golang struct is named collection of data fields. These fields can be of different types. Struct acts as a container that has different heterogeneous data types which together represents an entity. For example, different attributes are used to represent an employee in an organization. Employee can have:

Name of string type
Age of int type
DOB of time.Time type
Salary of int type

A pointer in golang is a variable that holds a memory address of another variable.

Now we have understood what struct and pointer is, let’s move unto how we can define a pointer to the struct.

Let’s say we have an employee struct

type employee struct {
    name   string
    age    int
    salary int
}

There are two ways of creating a pointer to the struct

Using the & operator

Using the new keyword

Let’s looks at each of above method one by one.

Using the & operator

The & operator can be used to get the pointer to a struct variable.

emp := employee{name: "Sam", age: 31, salary: 2000}
empP := &emp

struct pointer can also be directly created as well

empP := &employee{name: "Sam", age: 31, salary: 2000}

Let’s look at a program

package main

import "fmt"

type employee struct {
    name   string
    age    int
    salary int
}

func main() {
    emp := employee{name: "Sam", age: 31, salary: 2000}
    empP := &emp
    fmt.Printf("Emp: %+v\n", empP)
    empP = &employee{name: "John", age: 30, salary: 3000}
    fmt.Printf("Emp: %+v\n", empP)
}

Output

Emp: &{name:Sam age:31 salary:2000}
Emp: &{name:John age:30 salary:3000}

Using the new keyword

Using the new() keyword will:

Create the struct

Initialize all the field to the zero default value of their type

Return the pointer to the newly created struct

This will return a pointer

empP := new(employee)

Pointer address can be print using the %p format modifier

fmt.Printf("Emp Pointer: %p\n", empP)

Also to note that * operator can be used to dereference a pointer which means getting the value at address stored in the pointer.

fmt.Printf("Emp Value: %+v\n", *empP)

It will print

Emp Value: {name: age:0 salary:0}

When not using the dereference pointer but using the format identifier %+v, then ampersand will be appended before the struct indicating that is a pointer.

fmt.Printf("Emp Value: %+v\n", empP)

It will print

Emp Value: &{name: age:0 salary:0}

Let’s see full program denoting above points

package main

import "fmt"

type employee struct {
    name   string
    age    int
    salary int
}

func main() {
    empP := new(employee)
    fmt.Printf("Emp Pointer Address: %p\n", empP)
    fmt.Printf("Emp Pointer: %+v\n", empP)
    fmt.Printf("Emp Value: %+v\n", *empP)
}

Output

Emp Pointer: 0xc0000a6020
Emp Value: &{name: age:0 salary:0}
Emp Value: {name: age:0 salary:0}

The pointer address printed will be different on your machine.

golang