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Go fmt Package

The fmt package (short for "format") is the most commonly used package for printing and reading data.

1. Printing Functions

There are three main ways to print output:

  • fmt.Println: Prints arguments with spaces between them and a newline at the end.
  • fmt.Print: Like Println, but no newline or extra spaces.
  • fmt.Printf: Used for formatted strings (incorporates "verbs" like %d).
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package main

import "fmt"

func main() {
    name := "Go"
    version := 1.21

    fmt.Println("Hello", name) // Prints "Hello Go" + \n
    fmt.Printf("%s version is %f\n", name, version)
}

2. Creating Strings (Sprintf)

If you want to "print" to a variable instead of the console, use fmt.Sprintf.

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s := fmt.Sprintf("Formatting %s into a string", "this")
fmt.Println(s)

3. Reading Input (Scan)

To get input from the user, use fmt.Scan or fmt.Scanln.

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package main

import "fmt"

func main() {
    var age int
    fmt.Print("Enter your age: ")
    fmt.Scan(&age) // Takes a pointer to the variable
    fmt.Println("Your age is:", age)
}

4. Errors (Errorf)

fmt.Errorf is a quick way to create a formatted error message.

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err := fmt.Errorf("user %d not found", 404)
fmt.Println(err.Error())

Quick Summary

Function Description
Print / Println Basic console output.
Printf Formatted console output.
Sprintf Returns a formatted string.
Scan Reads input from console.
Errorf Creates a formatted error.