How to Use fmt.Sprintf in Go: Simple Formatting Guide

In Go, fmt.Sprintf formats strings by inserting variables into a format string and returns the result without printing it. Use it by providing a format string with verbs like %s or %d followed by the values to insert.

Syntax

The basic syntax of fmt.Sprintf is:

• fmt.Sprintf(format string, values...)

Here, format string contains text and verbs like %s for strings, %d for integers, and %f for floats. The values are the variables you want to insert into the string.

go

result := fmt.Sprintf("Hello, %s! You have %d new messages.", "Alice", 5)

Example

This example shows how to use fmt.Sprintf to create a formatted string with a name and a number, then print it.

go

package main

import (
	"fmt"
)

func main() {
	name := "Bob"
	count := 3
	message := fmt.Sprintf("Hello, %s! You have %d new notifications.", name, count)
	fmt.Println(message)
}

Output

Hello, Bob! You have 3 new notifications.

Common Pitfalls

Common mistakes include:

• Using fmt.Sprintf but forgetting to assign or use the returned string.
• Mismatching verbs and variable types, like using %d for a string.
• Confusing fmt.Sprintf with fmt.Printf, which prints directly instead of returning a string.

go

package main

import (
	"fmt"
)

func main() {
	name := "Eve"
	age := 30

	// Wrong: Using %d for a string causes runtime error
	// message := fmt.Sprintf("Name: %d", name) // This will cause an error

	// Correct:
	message := fmt.Sprintf("Name: %s, Age: %d", name, age)
	fmt.Println(message)
}

Output

Name: Eve, Age: 30

Quick Reference

Verb	Description	Example
%s	String	"hello"
%d	Integer (base 10)	123
%f	Floating point number	3.14
%t	Boolean	true
%v	Default format	any value
%%	Literal percent sign	%

Key Takeaways

Use fmt.Sprintf to format strings and get the result as a string without printing.

Match format verbs like %s and %d correctly with variable types to avoid errors.

Remember fmt.Sprintf returns a string; use fmt.Printf to print directly.

Assign the result of fmt.Sprintf to a variable to use the formatted string later.

Common verbs include %s for strings, %d for integers, and %f for floats.