PHP include_once statement

PHP include_once statement is very similar to PHP include statement but the only difference is include_once statement include PHP file only one time in any page. On the other hand, PHP include statement include a file many times.  

Structure: 

The structure of PHP include_statement is 

                        include_once("FileName") 

                            include_once("function.php")

Example:

Suppose that, we have three PHP file where first one has a function that print 0 to 10. Second PHP file include the first file and show the output. The third one add those two file. Now the code snippet are 

first.php

<?php
function foo()
{
    for($variable=0; $variable<10;$variable++)
    {
        echo $variable;
        echo "<br>";
        }
}
?>

Now the second file which one show the function value and second file name is  second.php

<?php
include("first_code.php");
foo();
?>

Third file is third.php

<?php
include("comments.php");
include("first_code.php");
?>

Try to run the third code. This code show an error message like this

Fatal error: Cannot redeclare foo()  previously declared  

This occurs because foo function declare in two times. So we use include_once statement to solve this problem.

<?php
include("comments.php");
include_once("first_code.php");
?>

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