PHP exit() function related_PHP tutorial-PHP Tutorial-php.cn

PHP exit() function related_PHP tutorial

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Release： 2016-07-13 10:33:37

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I encountered a problem today and an error occurred when running the following code.

<?php
session_start();
if(!isset($_SESSION['user']) || null === $_SESSION['user'])
{
    header('location:login.php');
    exit;
}
?>

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The error message is:

    
Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at D:\PHPProjects\agilelite\index.php:1) in D:\PHPProjects\agilelite\index.php on line 2
Warning: Cannot modify header information - headers already sent by (output started at D:\PHPProjects\agilelite\index.php:1) in D:\PHPProjects\agilelite\index.php on line 6

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In order to solve this problem, study the usage of the exit function.

Return, break and continue are language structures, just like if statements, but exit is a function. The function of the exit function is to output a message and terminate the current script.

If a piece of text includes multiple scripts ending with , exit will exit the current script.

For example, if a php text includes the following code, the output will be NowaMagic.

<?php
	echo "Hello";
	exit;
?>
<?php
	echo "NowaMagic";
?>

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The exit function syntax format is as follows (void means no return value):

void exit ([ string $status ] )
void exit ( int $status )

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If status is a string, this function prints status before the script exits.

If status is an integer, this integer will be used as the exit status. Exit status should be from 0 to 254, exit status 255 is reserved by PHP and is prohibited from use. Status 0 is used to indicate successful termination of the procedure.

Use exit after header jump

PHP’s header can output http header information. The premise is that no content can be output before the header, because all content is output to the client as the http body. Once there is body content, it is impossible to add it. Any information in the head section.

A common way of header function is to use it for redirection.

For example, if I need to go to a certain address, I just need to execute the following code:

<?php
	header('Location: http://www.bkjia.com/');
?>

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The browser will receive a 302 http status code, telling it that the content has been transferred.

The important thing is that PHP will continue to execute the following code after calling the header function. You can try it yourself with my code:

<?php
header('Location: http://www.bkjia.com/');
$fp	= fopen('header.txt', 'w+');
fwrite($fp, date('Y-m-d H:i:s'));
?>

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The fwrite function will definitely be executed, open the header.txt file and check the time!

The solution is to add exit after each header function to ensure that the current page stops executing and then redirects to the address specified by location.

In order to avoid exits everywhere, you can write a function specifically used for steering, such as:

<?php
function DoRedirect($strUrl) {
	header('Location: ' . $strUrl);
	exit;
}
?>

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In addition, in order to avoid outputting the body content before the header, many PHP frameworks adopt the method of not writing ?> at the end of the PHP page, because some people are always used to adding a line break after ?>, which is really a bad thing habits.