Go program not waiting for input with scanf

Question

I've found some sort of similar problems in c, but the solutions are c specific. package main

Here is a minimum working example of the code

import "fmt"

func main() {
  var mode string
  var base int
  for {
    fmt.Printf("(Base) [-->]: ")
    fmt.Scanf("%d", &base)
    fmt.Printf("(Mode) [-->]: ")
    fmt.Scanf("%s", &mode)
  }
}

My issue is that after asking for the mode input, it doesn't wait for input, and immediately skips to the beginning of the loop. Something like this:

(Base) [-->]: 5
(Mode) [-->]: (Base) [-->]:

Your code works for me, on my machine, with 5 as the input for base and foo for mode, without the behaviour you described. Are you sure you, on your machine, can reproduce the error with the code in the question? and with the same input? If you really do get the weird behaviour then try checking the errors returned from Scanf. — mkopriva
– mkopriva, Commented Mar 21, 2021 at 14:29
stackoverflow.com/questions/26536746/…, stackoverflow.com/questions/13846522/golang-scanf-error, stackoverflow.com/questions/17401709/… — mkopriva
– mkopriva, Commented Mar 21, 2021 at 15:04
The \n one work for me. Odd that it still worked on linux though. — OctopuSS7
– OctopuSS7, Commented Mar 21, 2021 at 15:10

Latheesh V M Villa · Accepted Answer · 2022-09-28 14:08:28Z

1

I had the same problem, changefmt.Scanf("%d", &base) to fmt.Scanf("%d \n", &base). I think it's connected to output of Scanf() where extra newline not being consumed by first scanf. Above code may still work in some device without any errors.

import "fmt"

func main() {
  var mode string
  var base int
  for {
    fmt.Printf("(Base) [-->]: ")
    fmt.Scanf("%d \n", &base)
    fmt.Printf("(Mode) [-->]: ")
    fmt.Scanf("%s \n", &mode)
  }
}

edited Sep 28, 2022 at 14:08

answered Sep 28, 2022 at 14:02

Latheesh V M Villa

1051 silver badge8 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

OctopuSS7 Over a year ago

Yes, this fixes the issue. I think that it may be because of the windows terminal, as it works on mac and linux on all of the terminal emulators I've tried.

Amirhossein Aliakbarpour · Accepted Answer · 2024-01-11 16:50:27Z

0

You can use fmt.Scanln(&base) instead of fmt.Scanf("%d", &base):

import "fmt"

func main() {
    var mode string
    var base int
    for {
        fmt.Printf("(Base) [-->]: ")
        fmt.Scanln(&base)
        fmt.Printf("(Mode) [-->]: ")
        fmt.Scanln(&mode)
    }
}

Or line, _ := bufio.NewReader(os.Stdin).ReadString('\n') is a good alternative to reading the whole line.

For fmt.Scanf() newlines in the input must match newlines in the format.

edited Jan 11, 2024 at 16:50

answered Jan 11, 2024 at 16:32

Amirhossein Aliakbarpour

557 bronze badges

Collectives™ on Stack Overflow

Go program not waiting for input with scanf

2 Answers 2

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related