reflect.NumField() Function in Golang with Examples

Go language provides inbuilt support implementation of run-time reflection and allowing a program to manipulate objects with arbitrary types with the help of reflect package. The reflect.NumField() Function in Golang is used to get the number of fields in the struct v. To access this function, one needs to imports the reflect package in the program.

Syntax:

func (v Value) NumField() int

Parameters: This function does not accept any parameter.

Return Value: This function returns the number of fields in the struct v.

Below examples illustrate the use of the above method in Golang:

Example 1:

// Golang program to illustrate
// reflect.NumField() Function

package main

import (
    "fmt"
    "reflect"
)

// Main function
func main() {

    // use of StructOf method
    tt:= reflect.StructOf([]reflect.StructField{
        {
            Name: "Height",
            Type: reflect.TypeOf(0.0),
            Tag:  `json:"height"`,
        },
        {
            Name: "Name",
            Type: reflect.TypeOf("abc"),
            Tag:  `json:"name"`,
        },
    })

    fmt.Println(tt.NumField())

}

Output:

2

Example 2:

// Golang program to illustrate
// reflect.NumField() Function

package main

import (
    "fmt"
    "reflect"
)

type temp struct {
    ord      int
    cId int
}

// function to use the
// Field() method
func useKind(val interface{}) {

    // Kind() function is used
    // to find the kind
    if reflect.ValueOf(val ).Kind() == reflect.Struct {
        v := reflect.ValueOf(val )
        fmt.Println("Number of fields", v.NumField())
        for i := 0; i < v.NumField(); i++ {
            fmt.Printf("Field: %d \t type: %T \t value: %v\n",
                                     i, v.Field(i), v.Field(i))
        }
    }


}

// Main function
func main() {
    val := temp {
        ord: 1,
        cId: 513,
    }
    useKind(val)

}

Output:

Number of fields 2
Field: 0      type: reflect.Value      value: 1
Field: 1      type: reflect.Value      value: 513