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Golang append() Function with Examples

Golang | append() Function: Here, we are going to learn about the built-in append() function with its usages, syntax, and examples.
Submitted by IncludeHelp, on October 13, 2021 [Last updated : March 15, 2023]

append() Function

In the Go programming language, the append() is a built-in function that is used to append elements to the end of a slice and returns an updated slice.

It accepts two or more parameters (slice []Type, elems ...Type) and returns an updated slice.

Note: If it has sufficient capacity, the destination is resliced to accommodate the new elements. If it does not, a new underlying array will be allocated.

Syntax

func append(slice []Type, elems ...Type) []Type

Parameter(s)

• slice : Slice in which we have to append the elements.
• Elems... : One or more elements to append.

Return Value

The return type of the append() function is a []Type, it returns the updated slice.

Example 1

// Golang program to demonstrate the
// example of append() function

package main

import (
	"fmt"
)

func main() {
	// Creating int and string slices
	s1 := []int{10, 20, 30}
	s2 := []string{"Hello", "World"}

	// Printing types and values of slices
	fmt.Printf("%T, %v\n", s1, s1)
	fmt.Printf("%T, %q\n", s2, s2)

	// Appending the elements
	s1 = append(s1, 40, 50)
	s2 = append(s2, "How are you?", "Boys")

	// After appending,
	// Printing types and values of slices
	fmt.Println("After appending...")
	fmt.Printf("%T, %v\n", s1, s1)
	fmt.Printf("%T, %q\n", s2, s2)
}

Output

[]int, [10 20 30]
[]string, ["Hello" "World"]
After appending...
[]int, [10 20 30 40 50]
[]string, ["Hello" "World" "How are you?" "Boys"]

Example 2

// Golang program to demonstrate the
// example of append() function

package main

import (
	"fmt"
)

func main() {
	// Creating int and string slices
	s1 := []int{10, 20, 30}
	s2 := []string{"Hello", "World"}

	// Creating slices to append
	slice1 := []int{40, 50}
	slice2 := []string{"How're you?", "Boys"}

	// Printing types and values of slices
	fmt.Printf("%T, %v\n", s1, s1)
	fmt.Printf("%T, %q\n", s2, s2)

	// Appending the slices
	s1 = append(s1, slice1...)
	s2 = append(s2, slice2...)

	// After appending,
	// Printing types and values of slices
	fmt.Println("After appending...")
	fmt.Printf("%T, %v\n", s1, s1)
	fmt.Printf("%T, %q\n", s2, s2)
}

Output

[]int, [10 20 30]
[]string, ["Hello" "World"]
After appending...
[]int, [10 20 30 40 50]
[]string, ["Hello" "World" "How're you?" "Boys"]

Example 3

// Golang program to demonstrate the
// example of append() function
// Appending string to a byte slice

package main

import (
	"fmt"
)

func main() {
	// Creating a byte slice
	s := []byte("Hello ")

	// Printing type and value of slice
	fmt.Printf("%T, %q\n", s, s)

	// Appending the string to byte slice
	s = append(s, "How're you?"...)

	// After appending,
	// Printing type and value of slice
	fmt.Println("After appending...")
	fmt.Printf("%T, %q\n", s, s)
}

Output

[]uint8, "Hello "
After appending...
[]uint8, "Hello How're you?"

Golang builtin Package »

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