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

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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