Golang Program to Use Field Tags in the Definition of Struct Type

Structure in Golang is used to store different types of data in one place. ‘struct’ itself is a user-defined data type. The syntax of ‘struct’ in Golang is as follow:

Syntax:

type var_name struct
{
     var1  data_type
     var2  data_type
}

Structure in Golang is written to files like JSON. It is a data storage format. Golang provides packages in the standard library to write and retrieve structures to/from the JSON file. In the definition of structures, field tags are added to the field declaration which is used as the field name in JSON files.

Syntax:

type Book struct 
{
    Name    string  `json:"name"`
    Author  string  `json: "author"`
    Price   int     `json: "price"`
}

Below programs illustrate the use of field tags in the definition of struct type in Golang:

Program 1:

// Golang program to show how to use
// field tags in the definition of Struct
package main

import
(
    "encoding/json"
    "fmt"
)

type Book struct
{
    Name    string  `json:"name"`
    Author  string  `json: "author"`
    Price   int     `json: "price"`
}

func main() {

    var b Book

    b.Name = "DBMS"
    b.Author = "Navathe"
    b.Price = 850

    fmt.Println(b)

    // returns []byte which is b in JSON form.
    jsonStr, err := json.Marshal(b)
    if err != nil {
        fmt.Println(err.Error())
    }

    fmt.Println(string(jsonStr))
}

Output:

{DBMS Navathe 850}
{"name":"DBMS", "author":"Navathe", "price":850}

Program 2:

// Golang program to show how to use
// field tags in the definition of Struct
package main

import
(
    "encoding/json"
    "fmt"
)

type Fruit struct
{
    Name    string  `json:"name"`
    Quantity  string  `json: "quantity"`
    Price   int     `json: "price"`
}

func main() {

    var f Fruit

    f.Name = "Apple"
    f.Quantity = "2KG"
    f.Price = 100

    fmt.Println(f)

    // returns []byte which is f in JSON form.
    jsonStr, err := json.Marshal(f)
    if err != nil {
        fmt.Println(err.Error())
    }

    fmt.Println(string(jsonStr))
}

Output:

{Apple 2KG 100}
{"name":"Apple", "quantity":"2KG", "price":100}