How to format strings with fmt

yourbasic.org/golang

Basics

A format specifier is a string that contains the text you want to format plus some placeholders, called verbs, that tell the functions in the fmt package how to format your arguments.

In this example

fmt.Printf("Hex: %x.\n", 255) // "Hex: ff."

Use the special verb %%, which consumes no argument, to write a literal percent sign.

fmt.Printf("%d %%", 50) // "50 %"

Generic formatting: []int{1, 2}

Formatting Description Verb
[1 2] Default format %v
[]int{1, 2} Go-syntax format %#v
[]int The type of the value %T

Integer: 109

Formatting Description Verb
109 Base 10 %d
+109 Always show sign %+d
␣109 Width 4, right justify %4d
109␣ Width 4, left justify %-4d
0109 Width 4, pad with zero %04d
m Character %c
'm' Quoted character %q
1101101 Base 2 %b
155 Base 8 %o
6d Base 16, lowercase %x
6D Base 16, uppercase %X
0x6d Base 16, with leading 0x %#x
U+006D Unicode %U
U+006D 'm' Unicode with character %#U

Boolean

Use %t to format a boolean as true or false.

Pointer

Use %p to format a pointer in base 16 notation with leading 0x.

Float: 123.456

Formatting Description Verb
1.234560e+02 Scientific notation %e
123.456000 Decimal point, no exponent %f
123.46 Default width, precision 2 %.2f
␣␣123.46 Width 8, precision 2 %8.2f
123.456 Exponent as needed, necessary digits only %g

String or byte slice: "café"

Formatting Description Verb
café Plain string %s
␣␣café Width 6, right justify %6s
café␣␣ Width 6, left justify %-6s
"café" Quoted string %q
636166c3a9 Hex dump of byte values %x
63 61 66 c3 a9 Hex dump with spaces % x

Special values

Value Description
\a U+0007 alert or bell
\b U+0008 backspace
\f U+000C form feed
\n U+000A line feed or newline
\r U+000D carriage return
\t U+0009 horizontal tab
\v U+000b vertical tab
\\ U+005c backslash

Arbitrary values can be encoded with backslash escapes. There are four different formats:

The escapes \u and \U represent Unicode code points. The special values can be used in any "" string literal.

fmt.Println("\\caf\u00e9")
\café

Further reading

The String functions cheat sheet presents the top Go string functions.

Share this page: