How to print boolean value in Go?

Question

As we have %d for int. What is the format specifier for boolean values?

Gittle

Try a code example: play.golang.org/p/RDGQEryOLP – Crelin

Note that strconv.FormatBool(b) is much faster in case speed is important. – Overshadow

Answer 1

If you use fmt package, you need %t format syntax, which will print true or false for boolean variables.

See package's reference for details.

Tungus

Also note that the %v format will print a reasonable default string for any value. – Sibilla

If I try to take input a boolean value; any value starting from 't' is true and any other value is false. – Gittle

package main import fmt "fmt" func main(){ var flag bool fmt.Scanf("%t",&flag) fmt.Printf("%t",flag) } – Gittle

@Anuj Verma: When scanning input, fmt.Scanf had to deal somehow with any string you pass it. It can read values true and false correctly, and that's its main purpose. When it doesn't see neither true, nor false in the input, it goes another way: it takes only first character and returns true if it is 't' or false if it is anything else, i.g. not-'t'. Note, that the rest of the input is still available for scanning with other options. For example, try such code and check results with different inputs. – Tungus

Answer 2

%t is the answer for you.

package main
import "fmt"

func main() {
   s := true
   fmt.Printf("%t", s)
}

Hannis

Answer 3

Use %t to format a boolean as true or false.

Emptyheaded

This is a the same answer, but shortened of the accepted one, remember that if you want to answer you should check when you can add something the post does not contains – Incoordination

this answer shows what will be in the output. Super! – Conchoid

Answer 4

Some other options:

package main
import "strconv"

func main() {
   s := strconv.FormatBool(true)
   println(s == "true")
}

package main
import "fmt"

func main() {
   var s string
   // example 1
   s = fmt.Sprint(true)
   println(s == "true")
   // example 2
   s = fmt.Sprintf("%v", true)
   println(s == "true")
}

• https://golang.org/pkg/fmt#Sprint
• https://golang.org/pkg/fmt#Sprintf
• https://golang.org/pkg/strconv#FormatBool

Malefactor

Answer 5

In my case, I need the bool to be 0/1. Then, this works.

func b2int(b bool) int8 {
    if b { return 1 }
    return 0
}
fmt.Sprintf("%d", b2int(b))

Geodynamics

Answer 6

Expanding on the above answers to include types booleans.

To print standard bool use %t as mentioned above:

isItTrue = true

fmt.Printf("Is it true? %t", isItTrue)

To print typed bools use %v and dereference the variable:

var isItTrue bool = true

fmt.Printf("Is it true? %v", *isItTrue)

Leastwise