Open File Append Problem

[siegmar]

For my Data logging I want to append a new line.

var filename = "TEST_6.9_LOG.csv";
var f = require("Storage").open(filename , "a");
f.write("timestamp, x, y, z\n");
I always get a filename with the extension " \u0001" like TEST_6.9_LOG.csv\u0001 and the size of the file is zero.

[gfwilliams]

Hi - I believe you may be trying to read the file the wrong way. Files opened with require("Storage").open are handled differently so as to be appendable (and that's why you see the file with \u0001 prepended).

To open it for reading, you need to use var f = require("Storage").open(filename , "r"); and then f.readLine() - https://www.espruino.com/Reference#StorageFile has some examples

[siegmar]

Thank you very much for your your quick replay

f = require("Storage").open(filename,"w");
f.write("Hell");
f.write("o World\n");
f.write("Hello\n");
f.write("World 2\n");
f.write("Hello World 3\n");
same Problem the filename has the extension /u0001

[gfwilliams]

Yes, it will have a 1 at the start, because it is a special type of file. Read it the way I suggested with .open and it'll be fine. No need to worry about the 1 at the start

You can list storageFiles (the special for type) with a specific argument to .list

[fanoush]

same Problem the filename has the extension /u0001

that's how it works, storage files are in fact one consecutive block of data and cannot be appended, the StorageFile is a wrapper around such basic files and each time you append, new file with numbered suffix is created, see https://www.espruino.com/Reference#t_StorageFile

[gfwilliams]

each time you append, new file with numbered suffix is created

... sometimes. It allocates a big block for the file which it keeps modifying, and only allocates a new suffix when that block is full :)

[siegmar]

Thank you very much for your help. My logging ist working now. My solution bevor, was to read the complet log file , append my new line and then save it. This cost to much time and Energy. I think it is working now cheers Siegmar