fmt Format Verbs

fmt.Printf, fmt.Sprintf, fmt.Fprintf, and friends use % verbs to format values. This reference covers every verb, flag, and width/precision modifier in the Go standard library.

Official documentation: fmt package

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General

Verb	Meaning	Example output
%v	Default format	42, true, [1 2 3]
%+v	Struct with field names	{Name:Alice Age:30}
%#v	Go syntax representation	main.Person{Name:"Alice", Age:30}
%T	Type of the value	int, []string, main.Person
%%	Literal % sign	%

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Boolean

Verb	Meaning	Example output
%t	true or false	true

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Integer

Verb	Meaning	Example output
%d	Base 10	42
%b	Base 2 (binary)	101010
%o	Base 8 (octal)	52
%O	Base 8 with 0o prefix	0o52
%x	Base 16, lowercase	2a
%X	Base 16, uppercase	2A
%c	Unicode code point → character	* (for 42)
%q	Single-quoted character literal	'*'
%U	Unicode format	U+002A

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Floating-point

Verb	Meaning	Example output
%f	Decimal, no exponent	3.141593
%F	Same as %f	3.141593
%.2f	Decimal, 2 decimal places	3.14
%e	Scientific notation, lowercase	3.141593e+00
%E	Scientific notation, uppercase	3.141593E+00
%g	Shortest of %e / %f	3.141592653589793
%G	Shortest of %E / %F	3.141592653589793
%x	Hexadecimal notation, lowercase	-0x1.921fb54442d18p+01
%X	Hexadecimal notation, uppercase	-0X1.921FB54442D18P+01

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String and []byte

Verb	Meaning	Example output
%s	Plain string / byte slice	hello
%q	Double-quoted, Go-escaped	"hello\nworld"
%x	Hex encoding, lowercase	68656c6c6f
%X	Hex encoding, uppercase	68656C6C6F

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Pointer

Verb	Meaning	Example output
%p	Base-16 pointer address	0xc0000b4010

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Width, Precision and Flags

Syntax	Effect
%8d	Right-align in a field of width 8
%-8d	Left-align in a field of width 8
%08d	Zero-pad to width 8
%8.2f	Width 8, 2 decimal places
%+d	Always show sign (+42, -7)
% d	Space before positive numbers ( 42)
%#x	Alternate form: add 0x prefix
%#o	Alternate form: add 0 prefix
%#b	Alternate form: add 0b prefix

Width and precision rules

• Width sets the minimum field width. The value is right-padded with spaces by default.
• Precision (.N) sets the number of decimal places for floats, or the maximum number of characters for strings.
• Combine both: %8.2f means width 8, 2 decimal places.
• For integers, precision sets the minimum number of digits: %.5d on 42 → 00042.

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When to Use Which Verb

Situation	Use
Printing any value during development	%v
Inspecting a struct and need field names	%+v
Generating valid Go source code	%#v
Checking what type a variable is	%T
Formatting a number for display	%d / %f
Formatting currency / fixed decimals	%.2f
Comparing string contents including escapes	%q
Printing a character from its code point	%c
Debugging memory addresses	%p
Encoding bytes as hex (e.g. hashes)	%x

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Examples

package main

import "fmt"

type Point struct{ X, Y int }

func main() {
    p := Point{3, 4}

    fmt.Printf("%v\n", p)          // {3 4}
    fmt.Printf("%+v\n", p)         // {X:3 Y:4}
    fmt.Printf("%#v\n", p)         // main.Point{X:3, Y:4}
    fmt.Printf("%T\n", p)          // main.Point

    fmt.Printf("%d %b %o %x\n", 42, 42, 42, 42)  // 42 101010 52 2a
    fmt.Printf("%08.2f\n", 3.14159)               // 00003.14
    fmt.Printf("%q\n", "hello\nworld")            // "hello\nworld"
    fmt.Printf("%10s|\n", "right")                //      right|
    fmt.Printf("%-10s|\n", "left")                // left      |
}