How to open file for writing?

Issue

I’m trying to open and write to a file using Dart’s IO library.

I have this code:

File file = File("text.txt");
RandomAccessFile raf = file.openSync();
raf.writeStringSync("A string!");

Now when doing this I get the following error in the console:

(OS Error: Access is denied., errno = 5)

So file is not opened for writing, and I’m looking here: open method, and can’t figure out how to use open or openSync to get RandomAccessFile I can write to.

It says I need to use write constant to do that but just can’t figure out how?
If I try to create FileMode and add it to open method as an argument I get an error saying:

Error: Too many positional arguments: 0 allowed, but 1 found.

So open and openSync methods can’t take any arguments, how would one use FileMode, and open method to open a file that is ready for writing? So I need to get RandomAccessFile that is in writing mode? And by default its only in read mode? I’m not trying to use writeString or writeStringSync, I know those methods exist, but I’m interested in how is this done using open and openSync methods that return RandomAccessFile!

Update:

Solution

You are getting this error:

Error: Too many positional arguments: 0 allowed, but 1 found.

because the openSync method has no positional arguments, but just one named parameter (mode).
So to fix your code you must add it:

RandomAccessFile raf = file.openSync(mode: FileMode.append); //Or whatever mode you'd to apply

Having said that, there are several other ways to write to a file, most of them listed in the docs:

• writeString or writeStringSync, I’d suggest these if what you need is just to write once to a file.

• openWrite, which returns a Stream that can be written in order to write to the file.

(All of these methods have a FileMode mode named parameter)

Answered By – Mattia

Answer Checked By – Candace Johnson (FlutterFixes Volunteer)