呼叫具有可能的格式指令

Question

When I run this code

package main
import ("fmt")
func main() {
    i := 5
    fmt.Println("Hello, playground %d",i)
}

(playground link)

I get the following warning: prog.go:5: Println call has possible formatting directive %d Go vet exited.

What is a proper way to do this?

Answer 1

fmt.Println doesn't do formatting things like %d. Instead, it uses the default format of its arguments, and adds spaces between them.

fmt.Println("Hello, playground",i)  // Hello, playground 5

If you want printf style formatting, use fmt.Printf.

fmt.Printf("Hello, playground %d
",i)

And you don't need to be particular about the type. %v will generally figure it out.

fmt.Printf("Hello, playground %v
",i)