Golang, is there a better way read a file of integers into an array?

Question

I need to read a file of integers into an array. I have it working with this:

package main

import (
    \"fmt\"
    \"io\"
    \"os\"
)

func readFile(filePath         


        

Answer 1

Your solution with fmt.Fscanf is fine. There are certainly a number of other ways to do though, depending on your situation. Mostafa's technique is one I use a lot (although I might allocate the result all at once with make. oops! scratch that. He did.) but for ultimate control you should learn bufio.ReadLine. See go readline -> string for some example code.

Answer 2

I would do it like this:

package main

import (
"fmt"
    "io/ioutil"
    "strconv"
    "strings"
)

// It would be better for such a function to return error, instead of handling
// it on their own.
func readFile(fname string) (nums []int, err error) {
    b, err := ioutil.ReadFile(fname)
    if err != nil { return nil, err }

    lines := strings.Split(string(b), "\n")
    // Assign cap to avoid resize on every append.
    nums = make([]int, 0, len(lines))

    for i, l := range lines {
        // Empty line occurs at the end of the file when we use Split.
        if len(l) == 0 { continue }
        // Atoi better suits the job when we know exactly what we're dealing
        // with. Scanf is the more general option.
        n, err := strconv.Atoi(l)
        if err != nil { return nil, err }
        nums = append(nums, n)
    }

    return nums, nil
}

func main() {
    nums, err := readFile("numbers.txt")
    if err != nil { panic(err) }
    fmt.Println(len(nums))
}

Answer 3

Using a bufio.Scanner makes things nice. I've also used an io.Reader rather than taking a filename. Often that's a good technique, since it allows the code to be used on any file-like object and not just a file on disk. Here it's "reading" from a string.

package main

import (
    "bufio"
    "fmt"
    "io"
    "strconv"
    "strings"
)

// ReadInts reads whitespace-separated ints from r. If there's an error, it
// returns the ints successfully read so far as well as the error value.
func ReadInts(r io.Reader) ([]int, error) {
    scanner := bufio.NewScanner(r)
    scanner.Split(bufio.ScanWords)
    var result []int
    for scanner.Scan() {
        x, err := strconv.Atoi(scanner.Text())
        if err != nil {
            return result, err
        }
        result = append(result, x)
    }
    return result, scanner.Err()
}

func main() {
    tf := "1\n2\n3\n4\n5\n6"
    ints, err := ReadInts(strings.NewReader(tf))
    fmt.Println(ints, err)
}