How to Format String in Go: Syntax and Examples

In Go, you format strings using fmt.Sprintf, which works like a template where placeholders are replaced by values. Use verbs like %s for strings, %d for integers, and %f for floats inside the format string.

Syntax

The basic syntax for formatting strings in Go uses fmt.Sprintf:

• fmt.Sprintf(format string, values...) returns a formatted string.
• The format string contains verbs like %s, %d, and %f as placeholders.
• values... are the variables you want to insert into the string.

go

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

Example

This example shows how to format a greeting message with a name and a number using fmt.Sprintf. It prints the formatted string.

go

package main

import (
	"fmt"
)

func main() {
	name := "Alice"
	messages := 5
	formatted := fmt.Sprintf("Hello, %s! You have %d new messages.", name, messages)
	fmt.Println(formatted)
}

Output

Hello, Alice! You have 5 new messages.

Common Pitfalls

Common mistakes include:

• Using the wrong verb for the data type, like %d for a string.
• Not matching the number of verbs with the number of values.
• Forgetting to import fmt package.

Here is an example of a wrong and right way:

go

package main

import (
	"fmt"
)

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

	// Wrong: using %d for string
	// formatted := fmt.Sprintf("Name: %d, Age: %d", name, age) // This causes a runtime error

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

Output

Name: Bob, Age: 30

Quick Reference

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

Key Takeaways

Use fmt.Sprintf with format verbs like %s, %d, and %f to format strings in Go.

Match the number and type of verbs with the values you provide to avoid errors.

Always import the fmt package to use formatting functions.

Use %v for a default format when unsure about the type.

Remember %% to print a literal percent sign in formatted strings.