Read from a file descriptor at given offset

# eio_read

(PECL eio >= 0.0.1dev)

eio_read — Read from a file descriptor at given offset

### Description

function eio_read(
mixed `$fd`,
int `$length`,
int `$offset`,
int `$pri`,
callable `$callback`,
mixed `$data` = NULL
): resource

eio_read() reads up to `length` bytes from `fd` file descriptor at `offset`. The read bytes are stored in `result` argument of `callback`.

### Parameters

`fd`
  Stream, Socket resource, or numeric file descriptor
`length`
  Maximum number of bytes to read.
`offset`
  Offset within the file.
`pri`
  The request priority: `EIO_PRI_DEFAULT`, `EIO_PRI_MIN`, `EIO_PRI_MAX`, or `null`. If `null` passed, `pri` internally is set to `EIO_PRI_DEFAULT`.
`callback`

  `callback` function is called when the request is done. It should match the following prototype:

      void callback(mixed $data, int $result[, resource $req]);

  `data`
    is custom data passed to the request.
  `result`
    request-specific result value; basically, the value returned by corresponding system call.
  `req`
    is optional request resource which can be used with functions like eio_get_last_error().
`data`
  Arbitrary variable passed to `callback`.

### Return Values

eio_read() stores read bytes in `result` argument of `callback` function.

### Examples

Example #1 eio_read() example

    <?php
    // Open a temporary file and write some bytes there
    $temp_filename = "eio-temp-file.tmp";
    $fp = fopen($temp_filename, "w");
    fwrite($fp, "1234567890");
    fclose($fp);

    /* Is called when eio_read() is done */
    function my_read_cb($data, $result) {
        global $temp_filename;

     // Output read bytes
        var_dump($result);

     // Close file
        eio_close($data);
        eio_event_loop();

     // Remove temporary file
        @unlink($temp_filename);
    }

    /* Is called when eio_open() is done */
    function my_file_opened_callback($data, $result) {
     // $result should contain the file descriptor
        if ($result > 0) {
      // Read 5 bytes starting from third
            eio_read($result, 5, 2, EIO_PRI_DEFAULT, "my_read_cb", $result);
            eio_event_loop();
        } else {
      // eio_open() failed
            unlink($data);
        }
    }

    // Open the file for reading and writing
    eio_open($temp_filename, EIO_O_RDWR, NULL,
        EIO_PRI_DEFAULT, "my_file_opened_callback", $temp_filename);
    eio_event_loop();
    ?>

The above example will output something similar to:

    string(5) "34567"

### See Also

- eio_open() - Opens a file
- eio_write() - Write to file
- eio_close() - Close file
- eio_event_loop() - Polls libeio until all requests proceeded

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