Convert integers to string

Avatar of the author Willem Schots
17 Jul, 2024
~2 min.
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In Go, you can’t directly cast an int to a string as you might in more loosely typed languages. Instead, you’ll need to format your integer as a string using one of several options.

This snippet will show you how to use the strconv and fmt packages to format integers as strings.

Using strconv.Itoa

The simplest way to convert an integer to a string is by using the strconv.Itoa function. This function will take your integer and format it as a base 10 integer.

“Itoa” stands for “Integer to ASCII”, based on a common C function of the same name.

See the example below:

main.go
package main

import (
	"fmt"
	"strconv"
)

func main() {
	i := 12345
	s := strconv.Itoa(i)
	fmt.Println("string:", s)
}

In this example the i integer is converted to string s using strconv.Itoa and then printed to stdout.

Using strconv.FormatInt

If you want to format your integer in a different base, strconv.FormatInt is the right choice.

For example, you can format your integer in binary (base 2) as follows:

main.go
package main

import (
	"fmt"
	"strconv"
)

func main() {
	i := int64(5) // strconv.FormatInt requires int64.
	s := strconv.FormatInt(i, 2)
	fmt.Println("string:", s)
}

Bases up to base 36 are supported, if an invalid base is provided the function will panic.

If you're using unsigned integers, use strconv.FormatUint instead.

Using the fmt package

So far we’ve only converted the integer to a string without including more text. But what if you want to include more?

You should take a look at the fmt package.

For example, the fmt.Sprintf function allows you to specify a layout string with a placeholder for the integer.

main.go
package main

import (
	"fmt"
)

func main() {
	i := 12345
	s := fmt.Sprintf("%d is the number", i)
	fmt.Println(s)
}

In this example, %d is the placeholder for a base 10 integer.

Other integer placeholders include:

placeholder format
%b base 2
%c the character represented by the corresponding Unicode code point
%d base 10
%o base 8
%O base 8 with 0o prefix
%q a single-quoted character literal safely escaped with Go syntax.
%x base 16, with lower-case letters for a-f
%X base 16, with upper-case letters for A-F
%U Unicode format: U+1234; same as "U+%04X"

In the fmt package documentation you can also find several flags that enable extra options for these placeholders.

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Willem Schots

Hello! I'm the Willem behind willem.dev

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