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Go Language Structs

In Go, arrays can store data of the same type, but in a struct, we can define different data types for different items.

A struct is a collection of data composed of fields with the same or different types.

A struct represents a record, such as saving book records in a library. Each book has the following attributes:

Defining a Struct

Struct definition requires the use of type and struct statements. The struct statement defines a new data type, with one or more members in the struct. The type statement sets the name of the struct. The format of a struct is as follows:

type struct_variable_type struct {
   member definition
   member definition
   ...
   member definition
}

Once the struct type is defined, it can be used for variable declaration, with the following syntax:

variable_name := struct_variable_type {value1, value2...valuen}
or
variable_name := struct_variable_type { key1: value1, key2: value2..., keyn: valuen}

Here is an example:

Example

package main

import "fmt"

type Books struct {
   title string
   author string
   subject string
   book_id int
}

func main() {
   // Create a new struct
   fmt.Println(Books{"Go Language", "www.tutorialpro.org", "Go Language Tutorial", 6495407})

   // Can also use key => value format
   fmt.Println(Books{title: "Go Language", author: "www.tutorialpro.org", subject: "Go Language Tutorial", book_id: 6495407})

   // Omitted fields are 0 or empty
   fmt.Println(Books{title: "Go Language", author: "www.tutorialpro.org"})
}

The output is:

{Go Language www.tutorialpro.org Go Language Tutorial 6495407}
{Go Language www.tutorialpro.org Go Language Tutorial 6495407}
{Go Language www.tutorialpro.org  0}

Accessing Struct Members

To access struct members, you need to use the dot . operator, with the following format:

struct.member_name

Struct type variables are defined using the struct keyword. Here is an example:

Example

package main

import "fmt"

type Books struct {
   title string
   author string
   subject string
   book_id int
}

func main() {
   var Book1 Books        /* Declare Book1 as type Books */
   var Book2 Books        /* Declare Book2 as type Books */

   /* Book 1 description */
   Book1.title = "Go Language"
   Book1.author = "www.tutorialpro.org"
   Book1.subject = "Go Language Tutorial"
   Book1.book_id = 6495407

   /* Book 2 description */
   Book2.title = "Python Tutorial"
   Book2.author = "www.tutorialpro.org"
   Book2.subject = "Python Language Tutorial"
   Book2.book_id = 6495700

   /* Print Book1 information */
   fmt.Printf("Book 1 title : %s\n", Book1.title)
   fmt.Printf("Book 1 author : %s\n", Book1.author)
   fmt.Printf("Book 1 subject : %s\n", Book1.subject)
   fmt.Printf("Book 1 book_id : %d\n", Book1.book_id)

   /* Print Book2 information */

fmt.Printf("Book 2 title: %s\n", Book2.title) fmt.Printf("Book 2 author: %s\n", Book2.author) fmt.Printf("Book 2 subject: %s\n", Book2.subject) fmt.Printf("Book 2 book_id: %d\n", Book2.book_id) }


The above example execution result is:

Book 1 title: Go Language Book 1 author: www.tutorialpro.org Book 1 subject: Go Language Tutorial Book 1 book_id: 6495407 Book 2 title: Python Tutorial Book 2 author: www.tutorialpro.org Book 2 subject: Python Language Tutorial Book 2 book_id: 6495700


---

## Structure as Function Argument

You can pass a structure type as an argument to a function just like any other data type, and access the structure variables in the same way as in the above example:

## Example

package main

import "fmt"

type Books struct { title string author string subject string book_id int }

func main() { var Book1 Books /* Declare Book1 of type Books / var Book2 Books / Declare Book2 of type Books */

/* book 1 specification */ Book1.title = "Go Language" Book1.author = "www.tutorialpro.org" Book1.subject = "Go Language Tutorial" Book1.book_id = 6495407

/* book 2 specification */ Book2.title = "Python Tutorial" Book2.author = "www.tutorialpro.org" Book2.subject = "Python Language Tutorial" Book2.book_id = 6495700

/* print Book1 info */ printBook(Book1)

/* print Book2 info */ printBook(Book2) }

func printBook(book Books) { fmt.Printf("Book title: %s\n", book.title) fmt.Printf("Book author: %s\n", book.author) fmt.Printf("Book subject: %s\n", book.subject) fmt.Printf("Book book_id: %d\n", book.book_id) }


The above example execution result is:

Book title: Go Language Book author: www.tutorialpro.org Book subject: Go Language Tutorial Book book_id: 6495407 Book title: Python Tutorial Book author: www.tutorialpro.org Book subject: Python Language Tutorial Book book_id: 6495700


---

## Structure Pointer

You can define pointers to structures just like you define pointers to any other variable, as follows:

var struct_pointer *Books


The pointer variable defined above can store the address of a structure variable. To get the address of the structure variable, place the `&` symbol in front of the structure variable:

struct_pointer = &Book1


To access the members of the structure using a pointer to that structure, use the `.` operator:

struct_pointer.title


Let's rewrite the above example using structure pointers, as follows:

## Example

package main

import "fmt"

type Books struct { title string author string subject string book_id int }

func main() { var Book1 Books /* Declare Book1 of type Books / var Book2 Books / Declare Book2 of type Books */

/* book 1 specification */ Book1.title = "Go Language" Book1.author = "www.tutorialpro.org" Book1.subject = "Go Language Tutorial" Book1.book_id = 6495407

/* book 2 specification */ Book2.title = "Python Tutorial" Book2.author = "www.tutorialpro.org" Book2.subject = "Python Language Tutorial" Book2.book_id = 6495700

/* print Book1 info */ printBook(&Book1)

/* print Book2 info */ printBook(&Book2) }

func printBook(book *Books) { fmt.Printf("Book title: %s\n", book.title) fmt.Printf("Book author: %s\n", book.author) fmt.Printf("Book subject: %s\n", book.subject) fmt.Printf("Book book_id: %d\n", book.book_id) }


The above example execution result is:

Book title: Go Language Book author: www.tutorialpro.org Book subject: Go Language Tutorial Book book_id: 6495407 Book title: Python Tutorial Book author: www.tutorialpro.org Book subject: Python Language Tutorial Book book_id: 6495700

/* book 1 description */ Book1.title = "Go Language" Book1.author = "www.tutorialpro.org" Book1.subject = "Go Language Tutorial" Book1.book_id = 6495407

/* book 2 description */ Book2.title = "Python Tutorial" Book2.author = "www.tutorialpro.org" Book2.subject = "Python Language Tutorial" Book2.book_id = 6495700

/* Print Book1 information */ printBook(&Book1)

/* Print Book2 information */ printBook(&Book2) } func printBook(book *Books) { fmt.Printf("Book title : %s\n", book.title) fmt.Printf("Book author : %s\n", book.author) fmt.Printf("Book subject : %s\n", book.subject) fmt.Printf("Book book_id : %d\n", book.book_id) }


The above example execution result is:

Book title : Go Language Book author : www.tutorialpro.org Book subject : Go Language Tutorial Book book_id : 6495407 Book title : Python Tutorial Book author : www.tutorialpro.org Book subject : Python Language Tutorial Book book_id : 6495700 ```

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