How to use fmt.Sscan to parse integers into an array? - go

Question

I'm trying to scan a list of integers from a string into an array (or alternatively, a slice)
package main
import "fmt"
func main() {
var nums [5]int
n, _ := fmt.Sscan("1 2 3 4 5", &nums) // doesn't work
fmt.Println(nums)
}
What do I need to pass as second argument to Sscan in order for this to work?
I know I could pass nums[0], nums[1] ... etc., but I'd prefer a single argument.

Answer 1

I don't think this is possible as a convenient one-liner. As Sscan takes ...interface{}, you would need to pass slice of interfaces as well, hence converting your array first:
func main() {
var nums [5]int
// Convert to interfaces
xnums := make([]interface{}, len(nums))
for n := range nums {
xnums[n] = &nums[n]
}
n, err := fmt.Sscan("1 2 3 4 5", xnums...)
if err != nil {
fmt.Printf("field %d: %s\n", n+1, err)
}
fmt.Println(nums)
}
http://play.golang.org/p/1X28J7JJwl
Obviously you could mix different types in your interface array, so it would make the scanning of more complex string easier. For simply space-limited integers, you might be better using strings.Split or bufio.Scanner along with strconv.Atoi.

Answer 2

To allow this to work on more than just hard-coded strings, it's probably better to use a bufio.Scanner, and an io.Reader interface to do this:
package main
import (
"bufio"
"fmt"
"io"
"strconv"
"strings"
)
func scanInts(r io.Reader) ([]int, error) {
s := bufio.NewScanner(r)
s.Split(bufio.ScanWords)
var ints []int
for s.Scan() {
i, err := strconv.Atoi(s.Text())
if err != nil {
return ints, err
}
ints = append(ints, i)
}
return ints, s.Err()
}
func main() {
input := "1 2 3 4 5"
ints, err := scanInts(strings.NewReader(input))
if err != nil {
fmt.Println(err)
}
fmt.Println(ints)
}
Produces:
[1 2 3 4 5]
Playground

Answer 3

Unless you're trying to use Sscann specifically you can also try this as an alternative:
split the input string by spaces
iterate the resulting array
convert each string into an int
store the resulting value into an int slice
Like this:
package main
import (
"fmt"
"strconv"
"strings"
)
func main() {
nums := make([]int, 0)
for _, s := range strings.Split("1 2 3 4 5", " ") {
i, e := strconv.Atoi(s)
if e != nil {
i = 0 // that was not a number, default to 0
}
nums = append(nums, i)
}
fmt.Println(nums)
}
http://play.golang.org/p/rCZl46Ixd4