CODEWITHSUNDEEP
node.jsfile-iofilesystems
pie3636
pie3636

Reputation: 814

node.js file system problems

I keep banging my head against the wall because of tons of different errors. This is what the code i try to use :

fs.readFile("balance.txt", function (err, data) //At the beginning of the script (checked, it works)
{
  if (err) throw err;
  balance=JSON.parse(data);;
});
fs.readFile("pick.txt", function (err, data)
{
  if (err) throw err;
  pick=JSON.parse(data);;
});

/*....
.... balance and pick are modified
....*/

if (shutdown)
{
        fs.writeFile("balance2.txt", JSON.stringify(balance));
        fs.writeFile("pick2.txt", JSON.stringify(pick));
        process.exit(0);
}

At the end of the script, the files have not been modified the slightest. I then found out on this site that the files were being opened 2 times simultaneously, or something like that, so i tried this :

var balance, pick;
var stream = fs.createReadStream("balance.txt");
stream.on("readable", function()
{
    balance = JSON.parse(stream.read());
});
var stream2 = fs.createReadStream("pick.txt");
stream2.on("readable", function()
{
    pick = JSON.parse(stream2.read());
});

/****
****/

fs.unlink("pick.txt");
            fs.unlink("balance.txt");
            var stream = fs.createWriteStream("balance.txt", {flags: 'w'});
            var stream2 = fs.createWriteStream("pick.txt", {flags: 'w'});
            stream.write(JSON.stringify(balance));
            stream2.write(JSON.stringify(pick));
            process.exit(0);

But, this time, both files are empty... I know i should catch errors, but i just don't see where the problem is. I don't mind storing the 2 objects in the same file, if that can helps. Besides that, I never did any javascript in my life before yesterday, so, please give me a simple explanation if you know what failed here.

Upvotes: 0

Views: 2277

Answers (1)

Brian
Brian

Reputation: 3334

What I think you want to do is use readFileSync and not use readFile to read your files since you need them to be read before doing anything else in your program (http://nodejs.org/api/fs.html#fs_fs_readfilesync_filename_options).

This will make sure you have read both the files before you execute any of the rest of your code.

Make your like code do this:

try
{
    balance = JSON.parse(fs.readFileSync("balance.txt"));
    pick = JSON.parse(fs.readFileSync("pick.txt"));
}
catch(err)
{    throw err;    }

I think you will get the functionality you are looking for by doing this.

Note, you will not be able to check for an error in the same way you can with readFile. Instead you will need to wrap each call in a try catch or use existsSync before each operation to make sure you aren't trying to read a file that doesn't exist.

How to capture no file for fs.readFileSync()?

Furthermore, you have the same problem on the writes. You are kicking off async writes and then immediately calling process.exit(0). A better way to do this would be to either write them sequentially asynchronously and then exit or to write them sequentially synchronously then exit.

Async option:

if (shutdown)
{
    fs.writeFile("balance2.txt", JSON.stringify(balance), function(err){
        fs.writeFile("pick2.txt", JSON.stringify(pick), function(err){
            process.exit(0);
        });
    });
}

Sync option:

if (shutdown)
{
    fs.writeFileSync("balance2.txt", JSON.stringify(balance));
    fs.writeFileSync("pick2.txt", JSON.stringify(pick));
    process.exit(0);
}

Upvotes: 1

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