Golang: Print String as Sequence of Byte, Char, Codepoint

Print One Byte in String

When you use a string index, example: "abc"[0], the value is a Byte.

You may print it as Hexadecimal , or integer (Unicode Codepoint), or as a char.

fmt.Printf("%#v", x[0])

Print as hexadecimal. Sample output: 0x61

fmt.Printf("%d", x[0])

Print as integer. Sample output: 97

fmt.Printf("%q", x[0])

Print as raw byte. Sample output: 'a'.

(May display as gibberish if the byte is a control character or non-printable ASCII Character.)

package main

import "fmt"

// ways to print 1 byte in string

func main() {

	var x = "abc"

	fmt.Printf("%#v\n", x[0]) // 0x61
	fmt.Printf("%d\n", x[0])  // 97
	fmt.Printf("%q\n", x[0])  // 'a'

}

Note, a index in string may not be a valid character.

package main

import "fmt"

// a index in string may not be a valid character

func main() {

	// utf8 encoding for FACE WITH TEARS OF JOY char is 4 bytes: F0 9F 98 82
	var y = "😂"

	// print 1st byte
	fmt.Printf("%#v\n", y[0]) // 0xf0
	fmt.Printf("%d\n", y[0])  // 240
	fmt.Printf("%q\n", y[0])  // 'ð'

}

Print Whole String

Because string is Byte sequence, you may want to print them in different ways.

Say you have a string like this: "♥\t😂", unicode heart followed by invisible Horizontal Tab (codepoint 9) followed by a emoji.

you may:

• Print string as text editor would display it.
• Print some char using escape sequence such as \t for tab.
• Print some char using unicode escape sequence such as \u2665.
• Print string as hexadecimal. (when you need to see the bytes).

The fmt.Printf function has several placeholders to help.

%s

Output raw bytes as is. If string contain ASCII Control Characters or byte sequence that is not a valid character, this can cause problem in the output terminal.

%q

Output in golang string syntax, using backslash escape sequence for non-printable characters. (e.g. "♥\t😂")

%+q

Output in golang string syntax, using backslash escape for anything that's not printable ASCII. (e.g. "\u2665\t\U0001f602")

% x

Hexadecimal, with space between each 2 digits. (e.g. e2 99 a5 09 f0 9f 98 82) This is best if you want to know the byte values.

[see ASCII Characters]

package main

import "fmt"

func main() {
	var x = "♥\t😂" // with a tab (U+0009) in middle

	fmt.Printf("%s\n", x)  // ♥ 😂
	fmt.Printf("%q\n", x)  // "♥\t😂"
	fmt.Printf("%+q\n", x) // "\u2665\t\U0001f602"
	fmt.Printf("% x\n", x) // e2 99 a5 09 f0 9f 98 82

}

Print String in Unicode Notation

To print string in unicode notation, example: U+2665 U+0009 U+1F602, first convert the string into Rune Slice , then print it with %U

Example:
fmt.Printf("%U\n", []rune(x))

package main

import "fmt"

func main() {
	// with a tab (U+0009) in middle
	var x = "♥\t😂"

	// turn the string into rune slice, then print it with %U
	fmt.Printf("%U\n", []rune(x)) // [U+2665 U+0009 U+1F602]
}