Why this example of fmt.Sscanf doesn't work?

[resal]

Hi,

I have a well-formatted input string and decided to use fmt.Sscanf to parse it. Here is a simple example (play link: http://play.golang.org/p/WlMpKiMGIv):

package main

import "fmt"

func main() {

format := "%6s%5d"

//      "ssssssddddd"

line := "some      3"

var str string

var numb int64

n, err := fmt.Sscanf(line, format, &str, &numb)

fmt.Println(n, err)

fmt.Println(str, numb)

}

And the output is:

1 EOF
some 0

Can you please point out why this doesn't work? 

Thanks.

[seppo...@gmail.com]

Scanning a string is space delimited. (http://golang.org/pkg/fmt/ -> Scanning)

In your case you have 7 spaces before '3', instead the maximum expected 5.

[seppo...@gmail.com]

Small error.

6 Spaces before '3' and expected maximum of 4 spaces before it.

 

[resal]

Hmm. So there must be space between the input arguments. I was under impression that when I specify "%6s" it would consume 6 characters and leaving the remaining 5 characters (4 spaces + '3') for "%5d". 

Then I guess I have to to slice the line and then parse the resulting fragments.

Thanks.

[Karol Mieczysław Marcjan]

W dniu czwartek, 25 grudnia 2014 23:22:36 UTC+1 użytkownik resal napisał:

Hmm. So there must be space between the input arguments. I was under impression that when I specify "%6s" it would consume 6 characters and leaving the remaining 5 characters (4 spaces + '3') for "%5d". 

Then I guess I have to to slice the line and then parse the resulting fragments.

Thanks.

Is there a particularily good reason to use a string instead of an io.Reader? You wouldn't have this problem if you were doing using fmt.Fscan with separate format strings for each argument.

-- Karol Marcjan

[Rob Pike]

I think the behavior is a bug and have filed https://github.com/golang/go/issues/9444 to settle the matter.

That said, there are more efficient ways to split fixed-format text than to use fmt.Scan.

-rob

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[resal]

I see. Thanks for the explanation.

For now I'm slicing these fixed-format lines to extract 12 fields (example code below). I'd appreciate it if you could give me pointers/sample code for better (e.g. more idiomatic or more efficient) ways to do the same task.

str := strings.TrimSpace(line[0:6])

numb, err :=  strconv.ParseInt(strings.TrimSpace(line[6:11]), 10, 64)

...

Thanks.

[Rob Pike]

I would use that approach myself. Don't forget to check for errors.

-rob