Unused variable outside of a for-loop in Go

Question

I can't compile the following Go code. I keep getting an error that variable 'header' is not used. I'm trying to read and process a CSV file. The file is read line by line an so I need to save the header into a "outside-the-loop" variable I can refer to when processing CSV lines. Anyone knows what I'm doing incorrectly as a new Go user?

func main() {
    ...
    inputData := csv.NewReader(file)
    var header []string
    //keep reading the file until EOF is reached
    for j := 0; ; j++ {
        i, err := inputData.Read()
        if err == io.EOF {
            break
        }
        if j == 0 {
            header = i
        } else {
            // Business logic in here
            fmt.Println(i)
            //TODO convert to JSON
            //TODO send to SQS
        }
    }
}

=> https://stackoverflow.com/help/minimal-reproducible-example — jub0bs, Feb 22 '22 at 20:04
The variable `header` is declared and assigned, but not used. To put this another way, the function does not read a value from the variable. — Charlie Tumahai, Feb 22 '22 at 20:08
okay, think I understand what you mean. Assigning a value to it does not count as 'using' it apparently. That's what confused me — michal-ko, Feb 22 '22 at 20:17

score 2 · Accepted Answer · answered Feb 22 '22 at 20:19

You can assign to a blank identifier just to be able to compile your code, like: _ = header. As example:

package main

import (
    "encoding/csv"
    "fmt"
    "io"
    "strings"
)

func main() {

    in := `first_name,last_name,username
"Rob","Pike",rob
Ken,Thompson,ken
"Robert","Griesemer","gri"
`
    file := strings.NewReader(in)
    inputData := csv.NewReader(file)
    var header []string
    //keep reading the file until EOF is reached
    for j := 0; ; j++ {
        i, err := inputData.Read()
        if err == io.EOF {
            break
        }
        if j == 0 {
            header = i
        } else {
            // Business logic in here
            fmt.Println(i)
            //TODO convert to JSON
            //TODO send to SQS
        }
    }

    _ = header
}

https://go.dev/play/p/BrmYU2zAc9f

Unused variable outside of a for-loop in Go

1 Answers1