# Shared Memory Functions

## Introduction

Shmop is an easy to use set of functions that allows PHP to read, write, create and delete Unix shared memory segments.

> Note: Versions of Windows previous to Windows 2000 do not support shared memory. Under Windows, Shmop will only work when PHP is running as a web server module, such as Apache or IIS (CLI and CGI will not work).

> Note: In PHP 4.0.3, these functions were prefixed by shm rather than shmop.

## Requirements

No external libraries are needed to build this extension.

## Installation

To use shmop you will need to compile PHP with the --enable-shmop parameter in your configure line.

## Runtime Configuration

This extension has no configuration directives defined in php.ini.

## Resource Types

## Predefined Constants

This extension has no constants defined.

## Examples

Example#1 Shared Memory Operations Overview

`<?php
// Create 100 byte shared memory block with system id of 0xff3
$shm_id = shmop_open(0xff3, "c", 0644, 100);
if (!$shm_id) {
echo "Couldn't create shared memory segment\n";
}
// Get shared memory block's size
$shm_size = shmop_size($shm_id);
echo "SHM Block Size: " . $shm_size . " has been created.\n";
// Lets write a test string into shared memory
$shm_bytes_written = shmop_write($shm_id, "my shared memory block", 0);
if ($shm_bytes_written != strlen("my shared memory block")) {
echo "Couldn't write the entire length of data\n";
}
// Now lets read the string back
$my_string = shmop_read($shm_id, 0, $shm_size);
if (!$my_string) {
echo "Couldn't read from shared memory block\n";
}
echo "The data inside shared memory was: " . $my_string . "\n";
//Now lets delete the block and close the shared memory segment
if (!shmop_delete($shm_id)) {
echo "Couldn't mark shared memory block for deletion.";
}
shmop_close($shm_id);
?>`

## Table of Contents

- shmop_close — Close shared memory block
- shmop_delete — Delete shared memory block
- shmop_open — Create or open shared memory block
- shmop_read — Read data from shared memory block
- shmop_size — Get size of shared memory block
- shmop_write — Write data into shared memory block