Format verbs
- Go course
- Intermediate
- Lesson 54/80
- 4 min
Learn common verbs like %v, %d and %s.
Verbs
The most common verbs:
%v default format {Ada 36}
%+v with field names {Ad:Ada Yas:36}
%#v Go syntax main.Kisi{Ad:"Ada", Yas:36}
%T type main.Kisi
%d integer %x hex %b binary
%s string %q quoted string
%f decimal %e scientific
%t bool %p pointer
%% a percent signWhen debugging, %+v and %#v show a value's contents most clearly.
The Stringer interface
If a type has a String() string method, %v and %s use it:
type Renk int
func (r Renk) String() string {
return [...]string{"kırmızı", "yeşil", "mavi"}[r]
}
fmt.Println(Renk(1)) // yeşilError() string plays the same role for errors. Careful: calling fmt.Sprintf("%v", r) inside String causes infinite recursion.
Practice Write a Stringer
For type Durum int, define the constants Aktif (0) and Pasif (1) with iota. The String() method returns "aktif"/"pasif". Print fmt.Printf("%v %d\n", Pasif, Pasif).
Starter code
package main
import "fmt"
func main() {
// buraya yaz
}Sample solution
package main
import "fmt"
type Durum int
const (
Aktif Durum = iota
Pasif
)
func (d Durum) String() string {
if d == Aktif {
return "aktif"
}
return "pasif"
}
func main() {
fmt.Printf("%v %d\n", Pasif, Pasif)
}Expected output
pasif 1
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does <code>fmt.Printf("%q", "a\tb")</code> print?
- a\tb
- %q
- "a\tb" (escaped and quoted) Correct answer
- a b
Explanation: %q writes the value in Go string syntax, escaping special characters; ideal for spotting invisible characters.
2 Print the type
Question
fmt.Printf("____
", 3.5) // float64
Answer
fmt.Printf("%T
", 3.5) // float64Explanation: %T prints the value's Go type.
3 Verb and output
| Term | Meaning |
|---|---|
%v |
{Ada 36} |
%+v |
{Ad:Ada Yas:36} |
%T |
main.Kisi |
%x (255) |
ff |