CODEWITHSUNDEEP
go
Graham Slick
Graham Slick

Reputation: 6870

Get offset/position of bytes written to file

I'm writing a string to a file, and I'd like to get the offset of the string which was just written. Here is the code writing the file:

package main

import (
    "os"
)

func main() {
    path := "test_file.txt"
    byteString := []byte("string to write")

    f, err := os.OpenFile(path, os.O_APPEND|os.O_WRONLY, 0600)
    if err != nil {
        panic(err)
    }

    defer f.Close()

    if _, err = f.Write(byteString); err != nil {
        panic(err)
    }
}

How can I get the offset after having written the line ?

Upvotes: 2

Views: 494

Answers (1)

Raghav Sood
Raghav Sood

Reputation: 82553

os.Write only returns the length of the bytes written. If you want the offset, you can either:

  1. Call os.Stat before writing, and then use os.WriteAt to write at the offset for the end of the file provided by the FileInfo structure.
  2. Call os.Stat after writing, and subtract the length written to the file from the new size.

Upvotes: 1

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