create_function

(PHP 4 >= 4.0.1, PHP 5)

create_function -- Create an anonymous (lambda-style) function

Description

string create_function ( string args, string code )

Creates an anonymous function from the parameters passed, and returns a unique name for it. Usually the args will be passed as a single quote delimited string, and this is also recommended for the code. The reason for using single quoted strings, is to protect the variable names from parsing, otherwise, if you use double quotes there will be a need to escape the variable names, e.g. \$avar.

You can use this function, to (for example) create a function from information gathered at run time:

Przykład 1. Creating an anonymous function with create_function()

<?php
$newfunc
= create_function('$a,$b', 'return "ln($a) + ln($b) = " . log($a * $b);');
echo
"New anonymous function: $newfunc\n";
echo
$newfunc(2, M_E) . "\n";
// outputs
// New anonymous function: lambda_1
// ln(2) + ln(2.718281828459) = 1.6931471805599
?>

Or, perhaps to have general handler function that can apply a set of operations to a list of parameters:

Przykład 2. Making a general processing function with create_function()

<?php
function process($var1, $var2, $farr)
{
    for (
$f=0; $f < count($farr); $f++) {
        echo
$farr[$f]($var1, $var2) . "\n";
    }
}

// create a bunch of math functions
$f1 = 'if ($a >=0) {return "b*a^2 = ".$b*sqrt($a);} else {return false;}';
$f2 = "return \"min(b^2+a, a^2,b) = \".min(\$a*\$a+\$b,\$b*\$b+\$a);";
$f3 = 'if ($a > 0 && $b != 0) {return "ln(a)/b = ".log($a)/$b; } else { return false; }';
$farr = array(
    
create_function('$x,$y', 'return "some trig: ".(sin($x) + $x*cos($y));'),
    
create_function('$x,$y', 'return "a hypotenuse: ".sqrt($x*$x + $y*$y);'),
    
create_function('$a,$b', $f1),
    
create_function('$a,$b', $f2),
    
create_function('$a,$b', $f3)
    );

echo
"\nUsing the first array of anonymous functions\n";
echo
"parameters: 2.3445, M_PI\n";
process(2.3445, M_PI, $farr);

// now make a bunch of string processing functions
$garr = array(
    
create_function('$b,$a', 'if (strncmp($a, $b, 3) == 0) return "** \"$a\" '.
    
'and \"$b\"\n** Look the same to me! (looking at the first 3 chars)";'),
    
create_function('$a,$b', '; return "CRCs: " . crc32($a) . " , ".crc32(b);'),
    
create_function('$a,$b', '; return "similar(a,b) = " . similar_text($a, $b, &$p) . "($p%)";')
    );
echo
"\nUsing the second array of anonymous functions\n";
process("Twas brilling and the slithy toves", "Twas the night", $garr);
?>

and when you run the code above, the output will be:

Using the first array of anonymous functions
parameters: 2.3445, M_PI
some trig: -1.6291725057799
a hypotenuse: 3.9199852871011
b*a^2 = 4.8103313314525
min(b^2+a, a^2,b) = 8.6382729035898
ln(a/b) = 0.27122299212594

Using the second array of anonymous functions
** "Twas the night" and "Twas brilling and the slithy toves"
** Look the same to me! (looking at the first 3 chars)
CRCs: -725381282 , 1908338681
similar(a,b) = 11(45.833333333333%)

But perhaps the most common use for of lambda-style (anonymous) functions is to create callback functions, for example when using array_walk() or usort()

Przykład 3. Using anonymous functions as callback functions

<?php
$av
= array("the ", "a ", "that ", "this ");
array_walk($av, create_function('&$v,$k', '$v = $v . "mango";'));
print_r($av);
?>

outputs:

Array
(
  [0] => the mango
  [1] => a mango
  [2] => that mango
  [3] => this mango
)

an array of strings ordered from shorter to longer

<?php

$sv
= array("small", "larger", "a big string", "it is a string thing");
print_r($sv);

?>

outputs:

Array
(
  [0] => small
  [1] => larger
  [2] => a big string
  [3] => it is a string thing
)

sort it from longer to shorter

<?php

usort
($sv, create_function('$a,$b','return strlen($b) - strlen($a);'));
print_r($sv);

?>

outputs:

Array
(
  [0] => it is a string thing
  [1] => a big string
  [2] => larger
  [3] => small
)



Język PHP to dzisiaj powszechnie przyjęty standard, podstawa tworzenia dynamicznych stron WWW, opartych na bazach danych.

PHP to język skryptowy. Znaczy to, że jest to język nie kompilowalny. Program jest wykonywany przez interpreter na podstawie jego kodu źródłowego. Język PHP to element technologii internetowej SERVER-SIDE. Znaczy to, że kod języka jest wykonywany od strony serwera (na serwerze).

W jakim celu używac PHP? Po co to komu?

Załóżmy, że potrzebujemy takiej strony internetowej, która wyświetli zawsze bieżącą datę. Dzięki technologii PHP, datę i godzinę odczytywać można z miejsca gdzie wykonuje się skrypt, np. gdy serwer znajduje się w USA a my w Polsce to widoczna jest różnica w czasie który zostanie wyświetlony.

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