Convert rune to int?

go type-conversion idioms rune
miku picture miku · Jan 24, 2014 · Viewed 35.1k times · Source

In the following code, I iterate over a string rune by rune, but I'll actually need an int to perform some checksum calculation. Do I really need to encode the rune into a []byte, then convert it to a string and then use Atoi to get an int out of the rune? Is this the idiomatic way to do it?

// The string `s` only contains digits.
var factor int
for i, c := range s[:12] {
    if i % 2 == 0 {
        factor = 1
    } else {
        factor = 3
    }
    buf := make([]byte, 1)
    _ = utf8.EncodeRune(buf, c)
    value, _ := strconv.Atoi(string(buf))
    sum += value * factor
}

On the playground: http://play.golang.org/p/noWDYjn5rJ

Answer

Gustavo Niemeyer picture Gustavo Niemeyer · Jan 24, 2014

The problem is simpler than it looks. You convert a rune value to an int value with int(r). But your code implies you want the integer value out of the ASCII (or UTF-8) representation of the digit, which you can trivially get with r - '0' as a rune, or int(r - '0') as an int. Be aware that out-of-range runes will corrupt that logic.

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