Write to a file, ends up with zero bytes

[Jon Kleiser]

Hi,

I want to write some text to a file, and I have tried both methods given at https://api.dartlang.org/stable/1.22.1/dart-io/File-class.html, both the one using "writeAsString" and the one using "sink.write", but both ways I end up with a completely empty file, zero bytes. Why is that happening?

/Jon

[Istvan Soos]

Hi Jon,

It might be possible that you are starting an async IO operation and
your program exits before it gets done. The following code should
work, because it awaits for the writeAsString() to be completed:

import 'dart:io';

main() async {
await new File('output.txt').writeAsString('content');
}

This article has a few more examples about Dart's IO uses:
https://www.dartlang.org/articles/dart-vm/io
Hope it helps.

Istvan

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[Jon Kleiser]

Thanks, Istvan. Yes, putting "await" in front of "new File" looks like it's the way to go. I just have to figure out a nice way to do the rest of the printing, unless I shall give the total content as one big string to 'writeAsString'.

/Jon

[Istvan Soos]

Keep in mind that the await is not "before" the "new File()", my code
was the short version of:

Future main() async {
File file = new File('output.txt');
Future f = file.writeAsString('content');
await f;

[Filip Hracek]

If you want to write to the file part-by-part (instead of one huge String), you can use File.sink. Just make sure you close it afterwards.

Filip Hráček
https://google.com/+filiphracek

[Bob Nystrom]

On Tue, Apr 4, 2017 at 1:09 PM, Jon Kleiser <jon.k...@usit.uio.no> wrote:

Thanks, Istvan. Yes, putting "await" in front of "new File" looks like it's the way to go. I just have to figure out a nice way to do the rest of the printing, unless I shall give the total content as one big string to 'writeAsString'.

Note that File also supports synchronous versions of most of its methods. If you don't need the asynchrony, I would recommend using the sync ones. So, in this case, you can just use writeAsStringSync().

Cheers!

– bob

[Jon Kleiser]

Thanks, all of you. I ended up with this:

    var randAccFile = new File(filename).openSync(mode: FileMode.WRITE_ONLY);

    randAccFile.writeStringSync("label\n");

    args.forEach((word) {

      randAccFile.writeStringSync("$word\n");

    });

    randAccFile.closeSync();

/Jon