Golang Working with pointers¶

Golang Working with pointers

Note: To execute golang code online you can use https://play.golang.org/

What is a pointer?¶

A pointer is a variable which holds the memory address of another variable.

When to use a pointer?¶

In golang we when using variables the variable passed as a value.
In some cases, we want to modify the data of a variable, for example we are passing a struct variable and want to update a field value. we can't do it because we are passing the value of a variable.
For this kind of cases we use pointers and update the data of a variable.
As we are not passing the value so, we are not using the extra bit of memory. By using pointers we can utilize the memory effectively.

Representing pointer in golang¶

We represent the pointers with *T where T is a name of pointer.
Let's write a simple program to see how to implement the pointers.

package main

import "fmt"

func main(){
    FullName := "Anjaneyulu Batta";
    var Name *string = &FullName;
    fmt.Printf("Type of Name is %T\n", Name)
    fmt.Println("Address of Name is", Name)
    // ouput: Type of Name is *string
    //        Address of Name is 0xc00010a220
}

Accessing value of a pointer in golang¶

To get the value of a pointer we can simply use a * in fron of the pointer variable. Let's see an example below

package main

import "fmt"

func main(){
    FullName := "Anjaneyulu Batta";
    var Name *string = &FullName;
    fmt.Println("Value of pointer Name is ", *Name)
    // ouput: Value of pointer Name is  Anjaneyulu Batta
}

Passing pointer to a function¶

Let's see a simple example to update the value of a pointer of type map.

package main

import "fmt"

type Employee struct{
    Name string
    ID   string
}

func UpdateEmployeeWithPointer(Emp *Employee){
    Emp.Name = "John"
    Emp.ID = "EMP002"
}

func UpdateEmployeeWithoutPointer(Emp Employee){
    Emp.Name = "John"
    Emp.ID = "EMP002"
}

func main(){
    emp := Employee{Name: "Anji", ID: "EMP001"}
    var empPointer *Employee = &emp;
    // call function UpdateEmployeeWithoutPointer
    UpdateEmployeeWithoutPointer(emp)
    fmt.Println(emp.Name, emp.ID)
    // output:  Anji EMP001

    // call function UpdateEmployeeWithPointer
    UpdateEmployeeWithPointer(empPointer)
    fmt.Println(emp.Name, emp.ID)
    // output:  John EMP002
}

Returning pointer from a function¶

It is perfectly legal for a function to return a pointer of a local variable. The Go compiler is intelligent enough and it will allocate this variable on the heap.

package main

import (  
    "fmt"
)

func returnPointer() *int {  
    i := 5
    return &i
}
func main() {  
    d := returnPointer()
    fmt.Println("Value of d", *d)
    // ouput: Value of d 5
}

Note: We don't need to work with array pointers as it's internally uses the pointer concept.

using slices for arrays instead pointers¶

Let's see a simple example

package main

import (  
    "fmt"
)

func modify(sls []int) {  
    sls[0] = 90
}

func main() {  
    a := [3]int{89, 90, 91}
    modify(a[:])
    fmt.Println(a)
    // [90 90 91]
}

We have covered simple cases, we can do more with pointers. But, be cautious when using pointers because it modifies the data.