Implementation of recursion in PHP (with example)

A recursive function is a function that calls itself. Be careful when writing recursive functions, because they can be recursive indefinitely. It is important to ensure that there are adequate methods to terminate recursion.

One: Use the parameter reference to complete the recursive function. The same piece of memory address is being manipulated.

<?php
$i=1;
functiontest(&$i)
{
echo$i;
$i++;
 if($i <10)
{
test($i);
}
}
test($i);//输出123456789

test($i);//输出10

?>

Second: Use global variables to complete the recursive function. A real global variable imported with the global statement inside a function field actually establishes a reference to a global variable. In the example, the $i inside the test () function is actually just one application of the variable $i in the first line of the program ($i = 1;);

<?php
$i= 1;
functiontest()
{
global$i;
 echo $i;
$i++;
 if ($i <10)
{
test();
}
}
test();//输出123456789

test();//输出10

?>

Three: Use static variables to complete the recursive function. static function: Initializes the variable only the first time it is called, and retains the value of the variable.

<?php
function test()
{
    static $i = 1;
    echo $i;

　　　　$i++;
    if ($i < 10) {
        test();
    }
    $i--;//在每一层递归结束时自减，这一句可以帮助理解递归函数的执行过程
}

test();//输出123456789

test();//输出123456789
?>

Example 1. cases where global variables are used recursively traverse all files under a folder

function GetFiles ($dir)

{

Global $arr;

if (Is_dir ($dir)) {

$hadle = @opendir ($dir);

while ($file =readdir ($hadle))

{

if (!in_array ($file, Array ('. ', '. ')))

{

$dirr = $dir. '/'. $file;

if (Is_dir ($DIRR))

{

getFiles ($DIRR);

}else{

Array_push ($arr, $DIRR);

}

}

}

}

}

$arr = Array ();

GetFiles (' e:/logs ');

Print_r ($arr);

　　

Example 2: Recursively traverse all files under a folder using a static variable

function GetFiles ($dir)

{

Static $arr = Array ();

if (Is_dir ($dir)) {

$hadle = Opendir ($dir);

while ($file =readdir ($hadle))

{

if (!in_array ($file, Array ('. ', '. ')))

{

$dirr = $dir. " /". $file;

if (Is_dir ($DIRR))

{

getFiles ($DIRR);

}else{

Array_push ($arr, $DIRR);

}

}

}

}

return $arr;

}

$rows = Array ();

$rows = GetFiles (' e:/logs ');

Print_r ($rows);

Implementation of recursion in PHP (with example)