Fscanf and omitting fields like in C

Question content

Is it possible to omit the field %*s like in C?

var pid int
fmt.Fscanf(r, "%*s %d", &pid)

Workaround

Actually, you can't do this in Go (at least on Go 1.21.0).

Source code shows:

• There are no verbs with omitted fields in the format string (like %*s in C): in fact, the verb of a string is always a single character (% s, %v, %q, %X or %X)
• Fscanf Method Iteration Parameters (Fscanf array in a(r io.Reader , format string, a...any)). Therefore, you mustdefine a parameter in a even if you don't care about its value

If you don’t want to define variables, you can use:

var pid int
fmt.Fscanf(r, "%s %d", new(string), &pid)

Other alternatives

For your specific case, to parse something in the reader, you can first read the reader into a string (e.g. io.ReadAll):

CB835C294C06824721603abd255bd78a

Then use the strings.Split method or regular expression, for example:

1. and strings.Split

pidString := strings.Split(string(s), " ")[1]
pid, err := strconv.Atoi(pidString)
if err != nil {
    panic(err) // handle the error
}

Use regular expressions:

re := regexp.MustCompile(`[^\s]+ (?P<pid>\d+)`) // similar to "%s %d"
matches := re.FindStringSubmatch(s)
pidString := matches[re.SubexpIndex("pid")]
pid, err := strconv.Atoi(pidString)
if err != nil {
    panic(err) // handle the error
}

There may be other methods, but these should suffice. Hope that helps.

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