os.Stdout is not buffered ?

[nicolas riesch]

I am a little confused with the buffering mode of Stdout, and fmt.Print behaviour.

If I am not mistaken, it seems that os.Stdout is not line buffered.

In fact, it is not buffered at all, as shown here :

  http://play.golang.org/p/8IrFdcETpt

Is the buffering mode of Stdin, Stdout and Stderr documented somewhere ? I haven't found so far ...

When the output of a Go program is redirected to a file, is there some block buffering taking place ?

If I want to create a "line buffered" Writer wrapping os.Stdout, f := bufio.NewWriter(os.Stdout) is not enough.

I should create a custom Writer type, with a Write(s) method calling Flush() if s contains '\n', correct ?

[Ian Lance Taylor]

On Wed, Aug 12, 2015 at 10:21 AM, nicolas riesch
<nicolas...@gmail.com> wrote:
>
> I am a little confused with the buffering mode of Stdout, and fmt.Print
> behaviour.
>
> If I am not mistaken, it seems that os.Stdout is not line buffered.
> In fact, it is not buffered at all, as shown here :
>
> http://play.golang.org/p/8IrFdcETpt

That is correct. os.Stdout is not buffered.

> Is the buffering mode of Stdin, Stdout and Stderr documented somewhere ? I
> haven't found so far ...

It's never really seemed necessary to explicitly document that they
are unbuffered. They are documented as being *os.File. A *os.File is
not buffered.

> When the output of a Go program is redirected to a file, is there some block
> buffering taking place ?

Not by the Go program. The operating system presumably does it.

> If I want to create a "line buffered" Writer wrapping os.Stdout, f :=
> bufio.NewWriter(os.Stdout) is not enough.
> I should create a custom Writer type, with a Write(s) method calling Flush()
> if s contains '\n', correct ?

Correct.

Ian

[nicolas riesch]

Aha moment:

In C, printf, fprintf functions write to a FILE *stream, and "stdout" is a "stream", not a file.

In Go, fmt.Print, fmt.Fprintf functions write directly to a file, not a Writer (equivalent to a C "stream").

It is just that the "stdout" word means different things in C and Go ...

Thank you for the explanation ;-)))

[Matt Harden]

io.Writer is not equivalent to a C "stream", whatever you meant by that. The only way you get (write) buffering in Go is if you are working with a bufio.Writer. C's standard library tends to buffer by default and you have to turn it off or use syscalls directly to avoid it. Go's standard library tends not to buffer by default and you need to wrap in bufio.* to get it. And don't forget to Flush() or Close() your files if they are buffered!

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[nicolas riesch]

Please ignore my last message.

In Go, fmt.Print, fmt.Fprintf functions also write to a Writer. But a File is just an unbuffered Writer.

I must be a little tired ...