In Golang, how to add results from a loop into a dynamic array of unknown size?

Question

The example I'm working with right now takes input from console asking for a file extension, say .txt . It searches the current directory for files and then does a Println which returns all the files with the .txt onto the screen.

For each result returned, how can I put each filename into an array (or a slice?) and then access each value later in the program to manipulate each file.

It doesn't need to be sequential.

This is the working code (modified from Adam Ng, I think)

     package main

  import (
      "fmt"
      "os"
      "path/filepath"
    "bufio"
    //"bytes"
    //"io/ioutil"

  )

  func main() {


    lineScan := bufio.NewScanner(os.Stdin)
    var inputText string

    fmt.Print("Enter file extension to search for: .extension \n")     
    lineScan.Scan()
    inputText = lineScan.Text()

      dirname := "." + string(filepath.Separator)

      d, err := os.Open(dirname)
      if err != nil {
          fmt.Println(err)
          os.Exit(1)
      }
      defer d.Close()

      files, err := d.Readdir(-1)
      if err != nil {
          fmt.Println(err)
          os.Exit(1)
      }

      for _, file := range files {
          if file.Mode().IsRegular() {

              if filepath.Ext(file.Name()) == inputText {

                fmt.Println(file.Name())
              }
          }
      }
  }

Go uses append to append to a slice. Is that what you're looking for? — Mr_Pink
– Mr_Pink, Commented Jan 11, 2017 at 18:27
This question, which is actually basic Go, would benefit from a more concise code black that consists of only your attempt to append to a slice in a loop. The answer could then be something much simpler. The details about opening files are unrelated to the question as stated. — ThatsAMorais
– ThatsAMorais, Commented Apr 27, 2018 at 16:04

daplho · Accepted Answer · 2017-01-11 18:38:59Z

3

I tweaked your code so that it will put each filename into a slice of strings and then print the slice at the end. Also, keep in mind that you already have a file list in the 'files' variable.

package main

import (
  "bufio"
  "fmt"
  "os"
  "path/filepath"
  //"bytes"
  //"io/ioutil"
)

func main() {

  lineScan := bufio.NewScanner(os.Stdin)
  var inputText string

  fmt.Print("Enter file extension to search for: .extension \n")
  lineScan.Scan()
  inputText = lineScan.Text()

  dirname := "." + string(filepath.Separator)

  d, err := os.Open(dirname)
  if err != nil {
    fmt.Println(err)
    os.Exit(1)
  }
  defer d.Close()

  files, err := d.Readdir(-1)
  if err != nil {
    fmt.Println(err)
    os.Exit(1)
  }

  fileList := make([]string, 0)
  for _, file := range files { 
    if file.Mode().IsRegular() {

      if filepath.Ext(file.Name()) == inputText {

        fmt.Println(file.Name())
        fileList = append(fileList, file.Name())
      }
    }
  }

  fmt.Println("File List: ", fileList)
}

I hope this works for you.

answered Jan 11, 2017 at 18:38

daplho

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3 Comments

Wilhelm de Fheur Gorm Over a year ago

I have a idea here of what you've done. I assume now that I can work with fileList in a while or a for each loop to pull each string out and do something with them. I would like a reference (for dummies like me) document or an example if you would be so kind.

Mr_Pink Over a year ago

@ArkhamAngel: The best reference is the documentation on appending slices, or even the append section of Effective Go. I would encourage you to go through the Tour Of Go, which cover all these basic Go concepts.

daplho Over a year ago

Here is an additional resource on appending to a slice for your reference

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