PHP Tutorials - Herong's Tutorial Examples - v5.17, by Herong Yang
ob_start() - Output Buffering Function
This section describes how to use the ob_start() function to turn on output buffering, which allows HTTP response header lines to be added after response body has been added.
As you can see from setcookie() definition, the PHP engine provides no buffer for the HTTP response body. That means as soon the PHP script starts to send output to the HTTP response body, the HTTP header block will be finalized, and not allowed to change any more.
But this default behavior can be altered by calling output control functions:
Of course, default behavior can also be altered by the configuration file, php.ini. Open php.ini and set the following line:
output_buffering = 4096
The above configuration line tells the PHP engine to turn on output buffering, and set the buffer size to 4096 bytes. Once "output_buffering" is turned on, you don't have to call ob_start() in your scripts.
To test the PHP engine default behavior, I modified CookieTest.php into CookieOutputBuffer.php:
<?php # CookieOutputBuffer.php #- Copyright 2003 (c) HerongYang.com. All Rights Reserved. # print("<pre>\n"); print("Adding cookies by the server:\n"); $numCookies = count( array_keys($_COOKIE) ); $numCookies++; $cookieName = "Cookie_$numCookies"; $cookieValue = "My cookie value"; print(" $cookieName: $cookieValue\n"); setcookie($cookieName, $cookieValue); print("\nCookies received by the server:\n"); foreach ($_COOKIE as $k => $v) { print " $k = $v\n"; } print "</pre>\n"; ?>
I then opened php.ini and set the following line:
output_buffering = 0
Running IE on CookieOutputBuffer.php gave me this:
Adding cookies by the server: Cookie_2: My cookie value Cookies received by the server: User = Herong Yang PHP Warning: Cannot modify header information - headers already sent by (output started at ...\CookieOutputBuffer.php:4) ...
Now I truly beblieve that PHP engine's default behavior is no output buffering. Make sure to change "output_buffering" back to 4096 before continuing to the next test.
Table of Contents
Introduction and Installation of PHP
PHP Data Types and Data Literals
Variables, References, and Constants
Expressions, Operations and Type Conversions
Conditional Statements - "if" and "switch"
Loop Statements - "while", "for", and "do ... while"
Function Declaration, Arguments, and Return Values
Interface with Operating System
Introduction of Class and Object
Integrating PHP with Apache Web Server
Retrieving Information from HTTP Requests
Creating and Managing Sessions in PHP Scripts
►Sending and Receiving Cookies in PHP Scripts
Sending and Receiving Cookies - Example
►ob_start() - Output Buffering Function
Persistent Cookies Saved on Hard Disk
Other Cookie Properties - Domain and Path
Controlling HTTP Response Header Lines in PHP Scripts
MySQL Server Connection and Access Functions
Functions to Manage Directories, Files and Images
SOAP Extension Function and Calling Web Services
SOAP Server Functions and Examples
Localization Overview of Web Applications
Using Non-ASCII Characters in HTML Documents
Using Non-ASCII Characters as PHP Script String Literals
Receiving Non-ASCII Characters from Input Forms
"mbstring" Extension and Non-ASCII Encoding Management
Managing Non-ASCII Character Strings with MySQL Servers
Parsing and Managing HTML Documents
Configuring and Sending Out Emails
Managing PHP Engine and Modules on macOS