shmop_read

(PHP 4 >= 4.0.4, PHP 5, PHP 7, PHP 8)

shmop_read — Read data from shared memory block

说明

shmop_read(Shmop $shmop, int $offset, int $size): string

shmop_read() will read a string from shared memory block.

参数

shmop: The shared memory block identifier created by shmop_open()
offset: Offset from which to start reading
size: The number of bytes to read. 0 reads shmop_size($shmid) - $start bytes.

返回值

Returns the data 或者在失败时返回 false.

更新日志

版本	说明
8.0.0	`shmop` expects a Shmop instance now; previously, a resource was expected.

范例

示例 #1 Reading shared memory block


<?php
$shm_data = shmop_read($shm_id, 0, 50);
?>

This example will read 50 bytes from shared memory block and place the data inside $shm_data.

参见

shmop_write() - Write data into shared memory block

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User Contributed Notes 5 notes

down

Craig Manley ¶

17 years ago


shmop_read() reads and returns the whole memory segment's data. This is not useful if you're just working with strings. If you need to read a string from shared memory, call str_from_mem() on the result of shmop_read(). Similarly when writing strings to memory (instead of binary data), null terminate your strings with str_to_nts() before passing the value on to shmop_write().

function str_to_nts($value) {
  return "$value\0";
}

function str_from_mem(&$value) {
  $i = strpos($value, "\0");
  if ($i === false) {
    return $value;
  }
  $result =  substr($value, 0, $i);
  return $result;
}

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macmaster at pobox dot com ¶

21 years ago


When i need to read the whole string at that shm pointer, setting the count parameter to zero (0) seems work for me.

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michael dot wuertz at six dot de ¶

1 year ago


With shmop_read, you probably get a "\0" - padded string.

$zero_padded = shmop_read($shm_seg, 0, 128);

$usable_string = rtrim($zero_padded, "\0");

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-1

slavapl at mailandnews dot com ¶

21 years ago


Also you can use the shmop_size() function to determine the block size.

down

-22

Milan Cvejic ¶

13 years ago


You should always serialize data written in shared memory.
And when you are reading data you should always unserialize.

<?php

$data = 'test';
$shm_bytes_written = shmop_write($shm_id, serialize($data), 0);
$shm_data = unserialize(shmop_read($shm_id, 0, $shm_bytes_written));
?>

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