# fsIOWrite<no value>
The **fsIOWrite** function is used to open a file and write data to it. Note that you can only write to files that have been saved to the `/work/` folder (see here for details: [Inaccessible Files](io-api/#inaccessible)).

 

##### Syntax

``` wasm
FsIOErr fsIOWrite(
    FsIOFile file,
    const char* pInBuffer,
    int byteOffset,
    int byteToWrite,
    FsIOFileWriteCallback callback,
    void* pUserData
);
```

 

##### Members

{{< table-wrapper >}}

| Parameters    | Description                                                                                                                                       |
|---------------|---------------------------------------------------------------------------------------------------------------------------------------------------|
| `file`        | This is the ID of a previously opened file, as returned by the `fsIOOpen` function.                                                               |
| `pInBuffer`   | This is a previously created buffer that contains the data to be written. The buffer should be at least of the size `byteToWrite` - `byteOffset`. |
| `byteOffset`  | This is the offset into the file to which data will be written.                                                                                   |
| `byteToWrite` | This defines the number of bytes to write to the file.                                                                                            |
| `callback`    | Callback (`FsIOFileWriteCallback`) that is sent when the write operation is finished.                                                             |
| `pUserData`   | Pointer given to the callback to identify the function call.                                                                                      |

{{< /table-wrapper >}}


 

##### Return Values

The function returns one of the `FsIOErr` codes.

 

##### Remarks

This function is non-blocking: it will not wait for the file to be read to pass to the next line of code.