Accessing struct fields in Go

Introduction

Structs group related data together. Accessing struct fields lets you get or change specific pieces of that data.

You want to store information about a person, like name and age, and then read or update those details.

You have a product with price and quantity, and you need to calculate total cost using those fields.

You want to organize settings for a game or app and access each setting separately.

You receive data from a sensor and want to read specific measurements stored in a struct.

Syntax

Go

structVariable.fieldName

Use the dot . to get or set a field inside a struct variable.

Field names start with a capital letter if you want to access them from other packages.

Examples

Set and print fields of a struct variable.

Go

type Person struct {
    Name string
    Age  int
}

var p Person
p.Name = "Alice"
p.Age = 30
fmt.Println(p.Name, p.Age)

Create a struct with values and access fields to print them.

Go

p := Person{Name: "Bob", Age: 25}
fmt.Println(p.Name)
fmt.Println(p.Age)

Change one field after creating the struct.

Go

type Point struct {
    X, Y int
}

pt := Point{X: 10, Y: 20}
pt.X = 15
fmt.Println(pt.X, pt.Y)

Sample Program

This program creates a Car struct, prints its fields, updates the Year field, and prints it again.

Go

package main

import "fmt"

type Car struct {
    Brand string
    Year  int
}

func main() {
    myCar := Car{Brand: "Toyota", Year: 2020}
    fmt.Println("Brand:", myCar.Brand)
    fmt.Println("Year:", myCar.Year)

    // Update the year
    myCar.Year = 2022
    fmt.Println("Updated Year:", myCar.Year)
}

Important Notes

If you have a pointer to a struct, you can access fields with the same dot syntax, Go handles the pointer automatically.

Trying to access a field that does not exist will cause a compile error.

Summary

Use structVariable.fieldName to access or change a struct's field.

Fields hold the data inside a struct and can be read or updated.

Structs help organize related data in one place.

Practice

1.

Which of the following is the correct way to access the Age field of a struct variable person in Go?

easy

A. person.Age()

B. person->Age

C. person["Age"]

D. person.Age

Solution

1. Step 1: Understand struct field access syntax in Go

   In Go, struct fields are accessed using dot notation: structVariable.fieldName.

2. Step 2: Apply to the given variable and field

   For variable person and field Age, the correct access is person.Age.

3. Final Answer:

   person.Age -> Option D

4. Quick Check:

   Use dot notation for struct fields = person.Age [OK]

Hint: Use dot (.) to access struct fields in Go [OK]

Common Mistakes:

• Using arrow (->) like in C/C++
• Trying to access fields like map keys
• Calling field as a function with ()

2.

Which of the following code snippets correctly accesses the Title field of a struct book?

type Book struct {
    Title string
    Author string
}

var book Book
// Access Title here

easy

A. book.Title

B. book->Title

C. book["Title"]

D. book.Title()

Solution

1. Step 1: Recall Go struct field access syntax

   Fields in Go structs are accessed using dot notation without parentheses or brackets.

2. Step 2: Apply to the book variable and Title field

   The correct syntax is book.Title.

3. Final Answer:

   book.Title -> Option A

4. Quick Check:

   Dot notation accesses struct fields = book.Title [OK]

Hint: Remember: struct fields use dot, not brackets or arrows [OK]

Common Mistakes:

• Using brackets like a map
• Using arrow operator (->)
• Calling field as a method

3.

What will be the output of the following Go program?

package main
import "fmt"

type Person struct {
    Name string
    Age  int
}

func main() {
    p := Person{Name: "Alice", Age: 30}
    fmt.Println(p.Age)
}

medium

A. Alice

B. 30

C. Name

D. Compilation error

Solution

1. Step 1: Understand struct initialization and field access

   The struct Person is initialized with Name: "Alice" and Age: 30. The variable p holds this struct.

2. Step 2: Identify the printed field

   The code prints p.Age, which is 30.

3. Final Answer:

   30 -> Option B

4. Quick Check:

   Print struct field Age = 30 [OK]

Hint: Print struct.field to get that field's value [OK]

Common Mistakes:

• Printing the Name field instead of Age
• Expecting field name as output
• Thinking code causes error

4.

Identify the error in the following Go code and choose the correct fix:

package main
import "fmt"

type Car struct {
    Model string
    Year  int
}

func main() {
    c := Car{Model: "Tesla", Year: 2022}
    fmt.Println(c->Model)
}

medium

A. Add parentheses: c.Model()

B. Change c->Model to c["Model"]

C. Change c->Model to c.Model

D. No error, code is correct

Solution

1. Step 1: Identify incorrect field access operator

   The code uses c->Model, which is invalid in Go. Go uses dot notation for struct fields.

2. Step 2: Correct the field access syntax

   Replace c->Model with c.Model to fix the error.

3. Final Answer:

   Change c->Model to c.Model -> Option C

4. Quick Check:

   Use dot (.) not arrow (->) for struct fields [OK]

Hint: Use dot (.) for struct fields, not arrow (->) [OK]

Common Mistakes:

• Using arrow operator like in C/C++
• Trying to access fields like map keys
• Calling field as a function

5.

Given the struct and code below, what will be the output?

package main
import "fmt"

type Employee struct {
    ID    int
    Name  string
    Title string
}

func main() {
    e := Employee{ID: 101, Name: "Bob", Title: "Developer"}
    e.Title = "Senior Developer"
    fmt.Println(e.Title)
}

hard

A. Senior Developer

B. Developer

C. Title

D. Compilation error

Solution

1. Step 1: Understand struct field update

   The struct Employee is created with Title: "Developer". Then the field Title is updated to "Senior Developer".

2. Step 2: Identify printed value

   The code prints e.Title after update, so output is Senior Developer.

3. Final Answer:

   Senior Developer -> Option A

4. Quick Check:

   Updated struct field prints new value [OK]

Hint: Assign new value with dot, then print updated field [OK]

Common Mistakes:

• Expecting original value instead of updated
• Thinking field cannot be changed
• Confusing field name with value