# create_function

(PHP 4 >= 4.0.1, PHP 5, PHP 7)

create_function — Create an anonymous (lambda-style) function

### 说明

create_function ( string `$args` , string `$code` ) : string

Creates an anonymous function from the parameters passed, and returns a unique name for it.

Caution

This function internally performs an eval() and as such has the same security issues as eval(). Additionally it has bad performance and memory usage characteristics.

If you are using PHP 5.3.0 or newer a native anonymous function should be used instead.

### 参数

Usually these parameters will be passed as single quote delimited strings. 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.

`args`

  The function arguments.

`code`

  The function code.

### 返回值

Returns a unique function name as a string, or `FALSE` on error.

### 范例

Example #1 Creating an anonymous function with create_function()

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

    <?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:

Example #2 Making a general processing function with create_function()

    <?php
    function process($var1, $var2, $farr)
    {
        foreach ($farr as $f) {
            echo $f($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);
    ?>

以上例程会输出：

    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, 342550513
    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()

Example #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);
    ?>

以上例程会输出：

    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);

    ?>

以上例程会输出：

    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);

    ?>

以上例程会输出：

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

### 参见

- Anonymous functions