🧾 Go Fmt Package – Format & Print Data with fmt in Go (2025 Guide)

🧲 Introduction – What Is the fmt Package in Go?

The fmt package in Go is part of its standard library, and it provides functions for formatted I/O operations. It’s one of the most used packages in Go, essential for printing output to the console, formatting strings, and even scanning input.

🎯 In this section, you’ll learn:

• How to use fmt.Print, fmt.Println, and fmt.Printf
• How fmt.Sprintf and fmt.Errorf work
• Format verbs (%s, %d, %f, etc.)
• The difference between printing and formatting-only functions

📦 Importing the fmt Package

Before using any fmt functions, you must import the package:

import "fmt"

All formatting functions (printing, scanning, string building) are accessed through this import.

🖨️ Output Functions in fmt

✅ fmt.Print()

Prints arguments as a single line, without a newline at the end.

fmt.Print("Hello, ")
fmt.Print("Go!")

📤 Output:

Hello, Go!

✅ fmt.Println()

Prints arguments with spaces between them and adds a newline at the end.

fmt.Println("Welcome", "to", "Go!")

📤 Output:

Welcome to Go!

✅ fmt.Printf()

Supports formatted output using verbs like %s, %d, %f, etc.

name := "Alice"
age := 30
fmt.Printf("%s is %d years old\n", name, age)

📤 Output:

Alice is 30 years old

🧠 Common Format Verbs in fmt

🧪 String Formatting with fmt

✅ fmt.Sprintf()

Formats a string and returns it without printing.

greeting := fmt.Sprintf("Hi, %s!", "Go Dev")
fmt.Println(greeting)

📤 Output:

Hi, Go Dev!

✅ fmt.Errorf()

Creates a custom error message using format verbs.

err := fmt.Errorf("Invalid input: %d", 404)
fmt.Println(err)

📤 Output:

Invalid input: 404

🧰 Real-World Example

package main

import (
    "fmt"
)

func main() {
    name := "John"
    age := 25
    isMember := true

    fmt.Print("Welcome, ")
    fmt.Println(name)

    fmt.Printf("Name: %s\nAge: %d\nMembership: %t\n", name, age, isMember)
}

📤 Output:

Welcome, John
Name: John
Age: 25
Membership: true

📌 Summary – Recap & Next Steps

The fmt package is Go’s powerful tool for formatting and displaying text. From simple messages to structured logs and error formatting, it’s foundational to any Go program.

🔍 Key Takeaways:

• Use fmt.Print, fmt.Println, and fmt.Printf for console output
• Use fmt.Sprintf to build formatted strings
• Use fmt.Errorf for formatted error messages
• Format verbs give precision over how data is presented

⚙️ Next: Learn about Go’s zero values, how uninitialized variables behave, and how to use them effectively.

❓ FAQs – Go fmt Package

❓ What’s the difference between Print and Println in fmt?
✅ Print() outputs without a newline; Println() adds a newline and separates arguments with spaces.

❓ When should I use Sprintf?
✅ Use Sprintf() when you want to store formatted strings in variables or pass them without printing.

❓ Can fmt format numbers with precision?
✅ Yes. For example, %.2f will format a float to 2 decimal places.

❓ What does %v do in fmt?
✅ %v prints values in their default format. It’s a shortcut for unknown types.

❓ Is fmt used only for printing?
✅ No. It’s also used for formatting strings and generating custom error messages.