Go Formatting Verbs - Go Tutorial

When working with the Printf() function in Go, you’ll have access to a variety of formatting verbs that allow you to control how data is presented.

General Formatting Verbs

The following are formatting verbs applicable to all kinds of data types:

Verb	Description
`%v`	Displays the value in the default format.
`%#v`	Outputs the value in Go-syntax format (ideal for debugging).
`%T`	Presents the type of the value.
`%%`	Prints out a percent sign.

Example Code:

package main

import ("fmt")

func main() {
    var speed = 120.75
    var brand = "Ducati"

    fmt.Printf("%v\n", speed)
    fmt.Printf("%#v\n", speed)
    fmt.Printf("%v%%\n", speed)
    fmt.Printf("%T\n", speed)

    fmt.Printf("%v\n", brand)
    fmt.Printf("%#v\n", brand)
    fmt.Printf("%T\n", brand)
}

Output:

120.75  
120.75  
120.75%  
float64  
Ducati  
"Ducati"  
string

Integer Formatting Verbs

These formatting verbs work exclusively with integers:

Verb	Description
`%b`	Displays the binary representation (base 2).
`%d`	Shows the decimal representation (base 10).
`%+d`	Shows the decimal representation including the sign.
`%o`	Displays the value in octal format (base 8).
`%O`	Octal format with a leading `0o`.
`%x`	Outputs the hexadecimal value (lowercase).
`%X`	Outputs the hexadecimal value (uppercase).
`%#x`	Hexadecimal format with a leading `0x`.
`%4d`	Pads spaces to make it width 4, right-aligned.
`%-4d`	Pads spaces to make it width 4, left-aligned.
`%04d`	Pads zeroes to make it width 4.

Example Code:

package main

import ("fmt")

func main() {
    var maxSpeed = 150

    fmt.Printf("%b\n", maxSpeed)
    fmt.Printf("%d\n", maxSpeed)
    fmt.Printf("%+d\n", maxSpeed)
    fmt.Printf("%o\n", maxSpeed)
    fmt.Printf("%O\n", maxSpeed)
    fmt.Printf("%x\n", maxSpeed)
    fmt.Printf("%X\n", maxSpeed)
    fmt.Printf("%#x\n", maxSpeed)
    fmt.Printf("%4d\n", maxSpeed)
    fmt.Printf("%-4d\n", maxSpeed)
    fmt.Printf("%04d\n", maxSpeed)
}

Output:

String Formatting Verbs

For string data types, here are the options:

Verb	Description
`%s`	Displays the string as it is.
`%q`	Wraps the string in double quotes.
`%8s`	Adjusts the width to 8, right-aligned.
`%-8s`	Adjusts the width to 8, left-aligned.
`%x`	Converts the string into hexadecimal format.
`% x`	Converts the string into hexadecimal format with spaces included.

Example Code:

package main

import ("fmt")

func main() {
    var motorcycleBrand = "Harley"

    fmt.Printf("%s\n", motorcycleBrand)
    fmt.Printf("%q\n", motorcycleBrand)
    fmt.Printf("%8s\n", motorcycleBrand)
    fmt.Printf("%-8s\n", motorcycleBrand)
    fmt.Printf("%x\n", motorcycleBrand)
    fmt.Printf("% x\n", motorcycleBrand)
}

Output:

Harley  
"Harley"  
   Harley  
Harley   
4861726c6579  
48 61 72 6c 65 79

Boolean Formatting Verbs

Boolean values have a straightforward formatting option:

Verb	Description
`%t`	Displays the value as `true` or `false`.

Example Code:

package main

import ("fmt")

func main() {
    var hasFuel = true
    var needsService = false

    fmt.Printf("%t\n", hasFuel)
    fmt.Printf("%t\n", needsService)
}

Output:

true  
false

Float Formatting Verbs

Here are formatting verbs that deal with floating-point numbers:

Verb	Description
`%e`	Shows the number in scientific notation with ‘e’.
`%f`	Displays the number with a decimal point but without an exponent.
`%.2f`	Limits the precision to 2 decimal points.
`%6.2f`	Adjusts the width to 6 and precision to 2.
`%g`	Uses the exponent only if necessary.

Example Code:

package main

import ("fmt")

func main() {
    var mileage = 25.768

    fmt.Printf("%e\n", mileage)
    fmt.Printf("%f\n", mileage)
    fmt.Printf("%.2f\n", mileage)
    fmt.Printf("%6.2f\n", mileage)
    fmt.Printf("%g\n", mileage)
}

Output:

2.576800e+01  
25.768000  
25.77  
  25.77  
25.768