Type Operators
Sinured: You can do the same thing with logical OR; if the first test is true, the second will never be executed.
<?PHP
if (empty($user_id) || in_array($user_id, $banned_list))
{
exit();
}
?>
Bölüm 11. Control Structures
Any PHP script is built out of a series of statements. A statement can be an assignment, a function call, a loop, a conditional statement of even a statement that does nothing (an empty statement). Statements usually end with a semicolon. In addition, statements can be grouped into a statement-group by encapsulating a group of statements with curly braces. A statement-group is a statement by itself as well. The various statement types are described in this chapter.
if
The if construct is one of the most important features of many languages, PHP included. It allows for conditional execution of code fragments. PHP features an if structure that is similar to that of C:
As described in the section about expressions, expr is evaluated to its Boolean value. If expr evaluates to TRUE, PHP will execute statement, and if it evaluates to FALSE - it'll ignore it. More information about what values evaluate to FALSE can be found in the 'Converting to boolean' section.
The following example would display a is bigger than b if $a is bigger than $b:
Often you'd want to have more than one statement to be executed conditionally. Of course, there's no need to wrap each statement with an if clause. Instead, you can group several statements into a statement group. For example, this code would display a is bigger than b if $a is bigger than $b, and would then assign the value of $a into $b:
If statements can be nested indefinitely within other if statements, which provides you with complete flexibility for conditional execution of the various parts of your program.
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User Contributed NotesControl Structures
wintermute
29-Aug-2007 12:45
29-Aug-2007 12:45
Sinured
01-Aug-2007 11:59
01-Aug-2007 11:59
As mentioned below, PHP stops evaluating expressions as soon as the result is clear. So a nice shortcut for if-statements is logical AND -- if the left expression is false, then the right expression can’t possibly change the result anymore, so it’s not executed.
<?php
/* defines MYAPP_DIR if not already defined */
if (!defined('MYAPP_DIR')) {
define('MYAPP_DIR', dirname(getcwd()));
}
/* the same */
!defined('MYAPP_DIR') && define('MYAPP_DIR', dirname(getcwd()));
?>
dougnoel
05-May-2006 06:29
05-May-2006 06:29
Further response to Niels:
It's not laziness, it's optimization. It saves CPUs cycles. However, it's good to know, as it allows you to optimize your code when writing. For example, when determining if someone has permissions to delete an object, you can do something like the following:
if ($is_admin && $has_delete_permissions)
If only an admin can have those permissions, there's no need to check for the permissions if the user is not an admin.
niels dot laukens at tijd dot com
26-Dec-2004 07:49
26-Dec-2004 07:49
For the people that know C: php is lazy when evaluating expressions. That is, as soon as it knows the outcome, it'll stop processing.
<?php
if ( FALSE && some_function() )
echo "something";
// some_function() will not be called, since php knows that it will never have to execute the if-block
?>
This comes in nice in situations like this:
<?php
if ( file_exists($filename) && filemtime($filename) > time() )
do_something();
// filemtime will never give an file-not-found-error, since php will stop parsing as soon as file_exists returns FALSE
?>