Golang bytes.IndexFunc() Function with Examples

Golang | bytes.IndexFunc() Function: Here, we are going to learn about the IndexFunc() function of the bytes package with its usages, syntax, and examples.
Submitted by IncludeHelp, on September 23, 2021

bytes.IndexFunc()

The IndexFunc() function is an inbuilt function of the bytes package which is used to get the byte index in the byte slice s (interpreted as a sequence of UTF-8-encoded code points) of the first Unicode code point satisfying f(c).

It accepts two parameters (s []byte, f func(r rune) bool) and returns the byte index in s of the first Unicode code point satisfying f(c), or -1 if none do.

Syntax

func IndexFunc(s []byte, f func(r rune) bool) int

Parameters

s : The byte slice in which we have to check the value satisfying the given bool function.
f : The bool function is used to check each byte of the byte slice (s).

Return Value

The return type of the bytes.IndexFunc() function is an int, it returns the byte index in s of the first Unicode code point satisfying f(c), or -1 if none do.

Example 1

// Golang program to demonstrate the
// example of bytes.IndexFunc() function

package main

import (
	"bytes"
	"fmt"
	"unicode"
)

func main() {
	f := func(c rune) bool {
		return !unicode.IsLetter(c)
	}

	// Returns the index of first non-letter
	fmt.Printf("%d\n", bytes.IndexFunc(
		[]byte("C211, RWA Flats, Delhi65"), f))

	// Returns the index of first non-letter
	fmt.Printf("%d\n", bytes.IndexFunc(
		[]byte("Okay@123!Hello..."), f))
}

Output:

1
4

Example 2

// Golang program to demonstrate the
// example of bytes.IndexFunc() function

package main

import (
	"bytes"
	"fmt"
	"unicode"
)

func main() {
	f1 := func(c rune) bool {
		return !unicode.IsLetter(c)
	}

	f2 := func(c rune) bool {
		return !unicode.IsNumber(c)
	}

	f3 := func(c rune) bool {
		return !unicode.IsLetter(c) && !unicode.IsNumber(c)
	}

	// Returns the index of first non-letter byte
	fmt.Printf("%d\n", bytes.IndexFunc(
		[]byte("C211, RWA Flats, Delhi65"), f1))

	// Returns the index of first non-number byte
	fmt.Printf("%d\n", bytes.IndexFunc(
		[]byte("Okay@123!Hello..."), f2))

	// Returns the index of first non-number & non-letter byte
	fmt.Printf("%d\n", bytes.IndexFunc(
		[]byte("Okay@123!Hello..."), f3))

	// Returns the index of first non-number & non-letter byte
	// It will return -1 because there are all letters
	fmt.Printf("%d\n", bytes.IndexFunc(
		[]byte("Hello"), f3))
}