How to bufio.Write with a length specified?

[Peng Yu]

Hi,

The following example shows how to write a byte slice to a buffer. But
what if I want only write a length shorter (say 2 instead of 5) than
the size of the slice. Is there a function that allows users to
specify the length to write? Thanks.

$ cat main.go
#!/usr/bin/env gorun
// vim: set noexpandtab tabstop=2:
package main

import (
"os"
"bufio"
"fmt"
)

func main() {
f := bufio.NewWriter(os.Stdout)
d := []byte{'s', 'o', 'm', 'e', '\n'}
n, err := f.Write(d)
f.Flush()
fmt.Printf("wrote %d bytes, error %q\n", n, err)
}

--
Regards,
Peng

[Bruno Albuquerque]

n, err := f.Write(d[:length]) ?

Where length is the amount of data you want to write.

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[Dan Kortschak]

If you want to write a length shorter than the slice, make the slice
shorter. No, seriously...

n, err := f.Write(d[:2])

[Peng Yu]

Dan & Bruno,

I didn't realize that it is as simple as that :) Thanks.

Does it involve any extra copy of the byte slice? Or f.Write literally
access the memory of d and only access 2 bytes of data for writing to
the buffer?

--
Regards,
Peng

[Bruno Albuquerque]

It creates a new slice header, but the backing array is not copied.

[Bruno Albuquerque]

Actually, it is even possible that not even a new slice header is created in this case, but I did not check.

[Marvin Renich]

* Peng Yu <peng...@gmail.com> [180118 18:37]:

> Dan & Bruno,
>
> I didn't realize that it is as simple as that :) Thanks.
>
> Does it involve any extra copy of the byte slice? Or f.Write literally
> access the memory of d and only access 2 bytes of data for writing to
> the buffer?

The blog entry https://blog.golang.org/go-slices-usage-and-internals
will give you some good info about this.

...Marvin