"invalid argument" coming from os.(*File).Read

skil...@psiimage.com

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May 25, 2016, 11:51:56 AM5/25/16

to golang-nuts

I started off with trying to parse a CSV file with encoding/csv.(*Reader).Read, but I was receiving an "invalid argument" error from that call. I then tried just using os.(*File).Read, but I'm getting the same error when I try to read a file into a buffer. Below is the code I am using:

package main

import (
	"fmt"
	"os"
)


func main() {
	filename := os.Args[1]
	fmt.Println("Filename:", filename)
	var f *os.File
	if f, err := os.Open(filename); err == nil {
		if f == nil {
			panic(fmt.Errorf("os.Open did not return an error but file did not open"))
		}
		defer func() {
			if err := f.Close(); err != nil {
				panic(err)
			}
		}()
	} else {
		panic(err)
	}
	b := make([]byte, 1024)
	if _, err := f.Read(b); err == nil {
		fmt.Println(string(b))
	} else {
		panic(err)
	}
}

os.(*File).Read is returning an "invalid argument" error, which according to the documentation I am reading here means that the receiver (I believe that is f) is nil, but I check for that! I'm getting this behavior with any file I try and on both Arch Linux x86 and Windows 10 x86_64. I'm hoping I'm overlooking something simple; any suggestions?

I tried the code I am using to read a CSV and replaced the *os.File returned by os.Open with the result of strings.NewReader (as exemplified in the encoding/csv documentation here) and then it works. What do I have to do for it to work with a file?

Thomas Bushnell, BSG

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May 25, 2016, 11:53:28 AM5/25/16

to skil...@psiimage.com, golang-nuts

The f you are declaring in the call to Open is shadowing the one at top level of the function, so that the one in the Read call.

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Sean Killian

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May 25, 2016, 12:29:28 PM5/25/16

to Thomas Bushnell, BSG, golang-nuts

That was it, thank you!

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Thank you,

Sean Killian
3494 Progress Drive, Suite A
Bensalem, PA 19020
skil...@psiimage.com
(215) 604-1330 x200

Dave Cheney

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May 25, 2016, 6:18:20 PM5/25/16

to golang-nuts, tbus...@google.com, skil...@psiimage.com

go vet can detect problems like this.

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