go readline -> string

Question

What is the idiomatic way to do a readline to string in Go? the raw functions provided in the standard library seem really low level, they return byte arrays. Is there any built in easier way to get a string out of a readline function?

Answer 1

I wrote up a way to easily read each line from a file. The Readln(*bufio.Reader) function returns a line (sans \n) from the underlying bufio.Reader struct.

// Readln returns a single line (without the ending \n)
// from the input buffered reader.
// An error is returned iff there is an error with the
// buffered reader.
func Readln(r *bufio.Reader) (string, error) {
  var (isPrefix bool = true
       err error = nil
       line, ln []byte
      )
  for isPrefix && err == nil {
      line, isPrefix, err = r.ReadLine()
      ln = append(ln, line...)
  }
  return string(ln),err
}

You can use Readln to read every line from a file. The following code reads every line in a file and outputs each line to stdout.

f, err := os.Open(fi)
if err != nil {
    fmt.Println("error opening file= ",err)
    os.Exit(1)
}
r := bufio.NewReader(f)
s, e := Readln(r)
for e == nil {
    fmt.Println(s)
    s,e = Readln(r)
}

Cheers!

Answer 2

Here's are some examples using bufio.ReadLine and bufio.ReadString.

 package main

import (
    "bufio"
    "fmt"
    "os"
)

func ReadLine(filename string) {
    f, err := os.Open(filename)
    if err != nil {
        fmt.Println(err)
        return
    }
    defer f.Close()
    r := bufio.NewReaderSize(f, 4*1024)
    line, isPrefix, err := r.ReadLine()
    for err == nil && !isPrefix {
        s := string(line)
        fmt.Println(s)
        line, isPrefix, err = r.ReadLine()
    }
    if isPrefix {
        fmt.Println("buffer size to small")
        return
    }
    if err != io.EOF {
        fmt.Println(err)
        return
    }
}

func ReadString(filename string) {
    f, err := os.Open(filename)
    if err != nil {
        fmt.Println(err)
        return
    }
    defer f.Close()
    r := bufio.NewReader(f)
    line, err := r.ReadString('\n')
    for err == nil {
        fmt.Print(line)
        line, err = r.ReadString('\n')
    }
    if err != io.EOF {
        fmt.Println(err)
        return
    }
}

func main() {
    filename := `testfile`
    ReadLine(filename)
    ReadString(filename)
}