Golang println function

last modified May 8, 2025

This tutorial explains how to use the println built-in function in Go. We'll cover basic output with practical examples of debugging and logging.

The println function is a built-in function in Go that writes to standard error. It's primarily used for debugging and temporary output during development. Unlike fmt.Println, it doesn't require imports.

In Go, println accepts multiple arguments of any type and prints space-separated values. It adds a newline at the end. The output format is implementation-dependent and may vary across platforms.

Basic println example

The simplest use of println outputs values to standard error. This example demonstrates basic printing of different value types.
Note: For production code, prefer fmt package.

basic_println.go

package main

func main() {
    println("Hello, Go!")
    println(42)
    println(3.14)
    println(true)
    println('A')
}

The example prints a string, integer, float, boolean, and rune. Each call to println outputs on a new line. The output format is basic.

Printing multiple values

println can accept multiple arguments of different types. This example shows how to print several values in one call.

multiple_values.go

package main

func main() {
    name := "Alice"
    age := 30
    height := 1.75
    
    println("Name:", name, "Age:", age, "Height:", height)
    
    a, b := 10, 20
    println("Values:", a, b, "Sum:", a+b)
}

The function prints all arguments space-separated. Expressions are evaluated before printing. The output format is less customizable than fmt.

Debugging with println

println is often used for quick debugging during development. This example demonstrates its use for variable inspection.

debugging.go

package main

func calculate(x, y int) int {
    println("calculate called with", x, y)
    result := x * y
    println("intermediate result:", result)
    return result + 1
}

func main() {
    a := 5
    b := 7
    println("Before calculation")
    res := calculate(a, b)
    println("Final result:", res)
}

The debug prints help track function calls and intermediate values. This is useful for quick diagnostics without proper logging setup.

Println vs fmt.Println

This example compares println with fmt.Println. It highlights formatting differences between the two approaches.

comparison.go

package main

import "fmt"

func main() {
    value := 3.141592653589793
    
    println("Built-in println:", value)
    fmt.Println("fmt.Println:", value)
    
    println("Built-in (struct):", struct{ x int }{42})
    fmt.Println("fmt.Println (struct):", struct{ x int }{42})
}

fmt.Println provides better formatting for complex types. Built-in println output is more basic and less consistent.

Println in goroutines

println can be safely used from multiple goroutines. This example demonstrates concurrent printing.

goroutines.go

package main

import (
    "sync"
    "time"
)

func worker(id int, wg *sync.WaitGroup) {
    defer wg.Done()
    println("Worker", id, "started")
    time.Sleep(time.Second)
    println("Worker", id, "finished")
}

func main() {
    var wg sync.WaitGroup
    
    for i := 1; i <= 3; i++ {
        wg.Add(1)
        go worker(i, &wg)
    }
    
    wg.Wait()
    println("All workers completed")
}

The output shows interleaved messages from different goroutines. println handles concurrent calls safely, though output may be mixed unpredictably.

Source

Go language specification

This tutorial covered the println function in Go with practical examples of debugging and temporary output scenarios.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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