PHP: Function arguments

Function arguments

Information may be passed to functions via the argument list, which is a comma-delimited list of expressions. The arguments are evaluated from left to right.

PHP supports passing arguments by value (the default), passing by reference, and default argument values. Variable-length argument lists are also supported.

Example #1 Passing arrays to functions


<?php
function takes_array($input)
{
    echo "$input[0] + $input[1] = ", $input[0]+$input[1];
}
?>

Passing arguments by reference

By default, function arguments are passed by value (so that if the value of the argument within the function is changed, it does not get changed outside of the function). To allow a function to modify its arguments, they must be passed by reference.

To have an argument to a function always passed by reference, prepend an ampersand (&) to the argument name in the function definition:

Example #2 Passing function parameters by reference


<?php
function add_some_extra(&$string)
{
    $string .= 'and something extra.';
}
$str = 'This is a string, ';
add_some_extra($str);
echo $str;    // outputs 'This is a string, and something extra.'
?>

Default argument values

A function may define C++-style default values for scalar arguments as follows:

Example #3 Use of default parameters in functions


<?php
function makecoffee($type = "cappuccino")
{
    return "Making a cup of $type.\n";
}
echo makecoffee();
echo makecoffee(null);
echo makecoffee("espresso");
?>

The above example will output:

Making a cup of cappuccino.
Making a cup of .
Making a cup of espresso.

PHP also allows the use of arrays and the special type NULL as default values, for example:

Example #4 Using non-scalar types as default values


<?php
function makecoffee($types = array("cappuccino"), $coffeeMaker = NULL)
{
    $device = is_null($coffeeMaker) ? "hands" : $coffeeMaker;
    return "Making a cup of ".join(", ", $types)." with $device.\n";
}
echo makecoffee();
echo makecoffee(array("cappuccino", "lavazza"), "teapot");
?>

The default value must be a constant expression, not (for example) a variable, a class member or a function call.

Note that when using default arguments, any defaults should be on the right side of any non-default arguments; otherwise, things will not work as expected. Consider the following code snippet:

Example #5 Incorrect usage of default function arguments


<?php
function makeyogurt($type = "acidophilus", $flavour)
{
    return "Making a bowl of $type $flavour.\n";
}
 
echo makeyogurt("raspberry");   // won't work as expected
?>

The above example will output:

Warning: Missing argument 2 in call to makeyogurt() in 
/usr/local/etc/httpd/htdocs/phptest/functest.html on line 41
Making a bowl of raspberry .

Now, compare the above with this:

Example #6 Correct usage of default function arguments


<?php
function makeyogurt($flavour, $type = "acidophilus")
{
    return "Making a bowl of $type $flavour.\n";
}
 
echo makeyogurt("raspberry");   // works as expected
?>

The above example will output:

Making a bowl of acidophilus raspberry.

Note: As of PHP 5, arguments that are passed by reference may have a default value.

Type declarations

Note:
Type declarations were also known as type hints in PHP 5.

Type declarations allow functions to require that parameters are of a certain type at call time. If the given value is of the incorrect type, then an error is generated: in PHP 5, this will be a recoverable fatal error, while PHP 7 will throw a TypeError exception.

To specify a type declaration, the type name should be added before the parameter name. The declaration can be made to accept NULL values if the default value of the parameter is set to NULL.

Valid types

Type	Description	Minimum PHP version
Class/interface name	The parameter must be an instanceof the given class or interface name.	PHP 5.0.0
self	The parameter must be an instanceof the same class as the one the method is defined on. This can only be used on class and instance methods.	PHP 5.0.0
array	The parameter must be an array.	PHP 5.1.0
callable	The parameter must be a valid callable.	PHP 5.4.0
bool	The parameter must be a boolean value.	PHP 7.0.0
float	The parameter must be a floating point number.	PHP 7.0.0
int	The parameter must be an integer.	PHP 7.0.0
string	The parameter must be a string.	PHP 7.0.0

Warning

Aliases for the above scalar types are not supported. Instead, they are treated as class or interface names. For example, using boolean as a parameter or return type will require an argument or return value that is an instanceof the class or interface boolean, rather than of type bool:


<?php
 function test(boolean $param) {}
 test(true);
 ?>

The above example will output:

 Fatal error: Uncaught TypeError: Argument 1 passed to test() must be an instance of boolean, boolean given, called in - on line 1 and defined in -:1

Examples

Example #7 Basic class type declaration


<?php
class C {}
class D extends C {}

// This doesn't extend C.
class E {}

function f(C $c) {
    echo get_class($c)."\n";
}

f(new C);
f(new D);
f(new E);
?>

The above example will output:

C
D

Fatal error: Uncaught TypeError: Argument 1 passed to f() must be an instance of C, instance of E given, called in - on line 14 and defined in -:8
Stack trace:
#0 -(14): f(Object(E))
#1 {main}
  thrown in - on line 8

Example #8 Basic interface type declaration


<?php
interface I { public function f(); }
class C implements I { public function f() {} }

// This doesn't implement I.
class E {}

function f(I $i) {
    echo get_class($i)."\n";
}

f(new C);
f(new E);
?>

The above example will output:

C

Fatal error: Uncaught TypeError: Argument 1 passed to f() must implement interface I, instance of E given, called in - on line 13 and defined in -:8
Stack trace:
#0 -(13): f(Object(E))
#1 {main}
  thrown in - on line 8

Example #9 Nullable type declaration


<?php
class C {}

function f(C $c = null) {
    var_dump($c);
}

f(new C);
f(null);
?>

The above example will output:

object(C)#1 (0) {
}
NULL

Strict typing

By default, PHP will coerce values of the wrong type into the expected scalar type if possible. For example, a function that is given an integer for a parameter that expects a string will get a variable of type string.

It is possible to enable strict mode on a per-file basis. In strict mode, only a variable of exact type of the type declaration will be accepted, or a TypeError will be thrown. The only exception to this rule is that an integer may be given to a function expecting a float. Function calls from within internal functions will not be affected by the strict_types declaration.

To enable strict mode, the declare statement is used with the strict_types declaration:

Caution

Enabling strict mode will also affect return type declarations.

Note:
Strict typing applies to function calls made from within the file with strict typing enabled, not to the functions declared within that file. If a file without strict typing enabled makes a call to a function that was defined in a file with strict typing, the caller's preference (weak typing) will be respected, and the value will be coerced.

Note:
Strict typing is only defined for scalar type declarations, and as such, requires PHP 7.0.0 or later, as scalar type declarations were added in that version.

Example #10 Strict typing


<?php
declare(strict_types=1);

function sum(int $a, int $b) {
    return $a + $b;
}

var_dump(sum(1, 2));
var_dump(sum(1.5, 2.5));
?>

The above example will output:

int(3)

Fatal error: Uncaught TypeError: Argument 1 passed to sum() must be of the type integer, float given, called in - on line 9 and defined in -:4
Stack trace:
#0 -(9): sum(1.5, 2.5)
#1 {main}
  thrown in - on line 4

Example #11 Weak typing


<?php
function sum(int $a, int $b) {
    return $a + $b;
}

var_dump(sum(1, 2));

// These will be coerced to integers: note the output below!
var_dump(sum(1.5, 2.5));
?>

The above example will output:

int(3)
int(3)

Example #12 Catching TypeError


<?php
declare(strict_types=1);

function sum(int $a, int $b) {
    return $a + $b;
}

try {
    var_dump(sum(1, 2));
    var_dump(sum(1.5, 2.5));
} catch (TypeError $e) {
    echo 'Error: '.$e->getMessage();
}
?>

The above example will output:

int(3)
Error: Argument 1 passed to sum() must be of the type integer, float given, called in - on line 10

Variable-length argument lists

PHP has support for variable-length argument lists in user-defined functions. This is implemented using the ... token in PHP 5.6 and later, and using the func_num_args(), func_get_arg(), and func_get_args() functions in PHP 5.5 and earlier.

... in PHP 5.6+

In PHP 5.6 and later, argument lists may include the ... token to denote that the function accepts a variable number of arguments. The arguments will be passed into the given variable as an array; for example:

Example #13 Using ... to access variable arguments


<?php
function sum(...$numbers) {
    $acc = 0;
    foreach ($numbers as $n) {
        $acc += $n;
    }
    return $acc;
}

echo sum(1, 2, 3, 4);
?>

The above example will output:

You can also use ... when calling functions to unpack an array or Traversable variable or literal into the argument list:

Example #14 Using ... to provide arguments


<?php
function add($a, $b) {
    return $a + $b;
}

echo add(...[1, 2])."\n";

$a = [1, 2];
echo add(...$a);
?>

The above example will output:

3
3

You may specify normal positional arguments before the ... token. In this case, only the trailing arguments that don't match a positional argument will be added to the array generated by ....

It is also possible to add a type hint before the ... token. If this is present, then all arguments captured by ... must be objects of the hinted class.

Example #15 Type hinted variable arguments


<?php
function total_intervals($unit, DateInterval ...$intervals) {
    $time = 0;
    foreach ($intervals as $interval) {
        $time += $interval->$unit;
    }
    return $time;
}

$a = new DateInterval('P1D');
$b = new DateInterval('P2D');
echo total_intervals('d', $a, $b).' days';

// This will fail, since null isn't a DateInterval object.
echo total_intervals('d', null);
?>

The above example will output:

3 days
Catchable fatal error: Argument 2 passed to total_intervals() must be an instance of DateInterval, null given, called in - on line 14 and defined in - on line 2

Finally, you may also pass variable arguments by reference by prefixing the ... with an ampersand (&).

Older versions of PHP

No special syntax is required to note that a function is variadic; however access to the function's arguments must use func_num_args(), func_get_arg() and func_get_args().

The first example above would be implemented as follows in PHP 5.5 and earlier:

Example #16 Accessing variable arguments in PHP 5.5 and earlier


<?php
function sum() {
    $acc = 0;
    foreach (func_get_args() as $n) {
        $acc += $n;
    }
    return $acc;
}

echo sum(1, 2, 3, 4);
?>

The above example will output:

add a note

User Contributed Notes 40 notes

down

php at richardneill dot org ¶

1 year ago


To experiment on performance of pass-by-reference and pass-by-value, I used this  script. Conclusions are below. 

#!/usr/bin/php
<?php
function sum($array,$max){   //For Reference, use:  "&$array"
    $sum=0;
    for ($i=0; $i<2; $i++){
        #$array[$i]++;        //Uncomment this line to modify the array within the function.
        $sum += $array[$i];  
    }
    return ($sum);
}

$max = 1E7                  //10 M data points.
$data = range(0,$max,1);

$start = microtime(true);
for ($x = 0 ; $x < 100; $x++){
    $sum = sum($data, $max);
}
$end =  microtime(true);
echo "Time: ".($end - $start)." s\n";

/* Run times:
#    PASS BY    MODIFIED?   Time
-    -------    ---------   ----
1    value      no          56 us
2    reference  no          58 us

3    valuue     yes         129 s
4    reference  yes         66 us

Conclusions:

1. PHP is already smart about zero-copy / copy-on-write. A function call does NOT copy the data unless it needs to; the data is
   only copied on write. That's why  #1 and #2 take similar times, whereas #3 takes 2 million times longer than #4.
   [You never need to use &$array to ask the compiler to do a zero-copy optimisation; it can work that out for itself.]

2. You do use &$array  to tell the compiler "it is OK for the function to over-write my argument in place, I don't need the original
   any more." This can make a huge difference to performance when we have large amounts of memory to copy.
   (This is the only way it is done in C, arrays are always passed as pointers)

3. The other use of & is as a way to specify where data should be *returned*. (e.g. as used by exec() ).
   (This is a C-like way of passing pointers for outputs, whereas PHP functions normally return complex types, or multiple answers
   in an array)

4. It's  unhelpful that only the function definition has &. The caller should have it, at least as syntactic sugar. Otherwise
   it leads to unreadable code: because the person reading the function call doesn't expect it to pass by reference. At the moment,
   it's necessary to write a by-reference function call with a comment, thus:
    $sum = sum($data,$max);  //warning, $data passed by reference, and may be modified.

5. Sometimes, pass by reference could be at the choice of the caller, NOT the function definitition. PHP doesn't allow it, but it
   would be meaningful for the caller to decide to pass data in as a reference. i.e. "I'm done with the variable, it's OK to stomp
   on it in memory".
*/
?>

down

gabriel at figdice dot org ¶

6 months ago


A function's argument that is an object, will have its properties modified by the function although you don't need to pass it by reference.

<?php
$x = new stdClass();
$x->prop = 1;

function f ( $o ) // Notice the absence of &
{
  $o->prop ++;
}

f($x);

echo $x->prop; // shows: 2
?>

This is different for arrays:

<?php
$y = [ 'prop' => 1 ];

function g( $a )
{
  $a['prop'] ++;
  echo $a['prop'];  // shows: 2
}

g($y);

echo $y['prop'];  // shows: 1
?>

down

carlos at wfmh dot org dot pl dot REMOVE dot COM ¶

6 years ago


You can use (very) limited signatures for your functions, specifing type of arguments allowed. 

For example:

public function Right( My_Class $a, array $b )

tells first argument have to by object of My_Class, second an array. My_Class means that you can pass also object of class that either extends My_Class or implements (if My_Class is abstract class) My_Class. If you need exactly My_Class you need to either make it final, or add some code to check what $a really.

Also note, that (unfortunately) "array" is the only built-in type you can use in signature. Any other types i.e.:

public function Wrong( string $a, boolean $b )

will cause an error, because PHP will complain that $a is not an *object* of class string (and $b is not an object of class boolean).

So if you need to know if $a is a string or $b bool, you need to write some code in your function body and i.e. throw exception if you detect type mismatch (or you can try to cast if it's doable).

down

Sergio Santana: ssantana at tlaloc dot imta dot mx ¶

11 years ago


PASSING A "VARIABLE-LENGTH ARGUMENT LIST OF REFERENCES" TO A FUNCTION
As of PHP 5, Call-time pass-by-reference has been deprecated, this represents no problem in most cases, since instead of calling a function like this:
   myfunction($arg1, &$arg2, &$arg3);

you can call it
   myfunction($arg1, $arg2, $arg3);

provided you have defined your function as 
   function myfuncion($a1, &$a2, &$a3) { // so &$a2 and &$a3 are 
                                                             // declared to be refs.
    ... <function-code>
   }

However, what happens if you wanted to pass an undefined number of references, i.e., something like:
   myfunction(&$arg1, &$arg2, ..., &$arg-n);?
This doesn't work in PHP 5 anymore.

In the following code I tried to amend this by using the 
array() language-construct as the actual argument in the 
call to the function.

<?php

  function aa ($A) {
    // This function increments each 
    // "pseudo-argument" by 2s
    foreach ($A as &$x) { 
      $x += 2;
    }
  }
 
  $x = 1; $y = 2; $z = 3;
  
  aa(array(&$x, &$y, &$z));
  echo "--$x--$y--$z--\n";
  // This will output:
  // --3--4--5--
?>

I hope this is useful.

Sergio.

down

Horst Schirmeier ¶

3 years ago


Editor's note: what is expected here by the parser is a non-evaluated expression. An operand and two constants requires evaluation, which is not done by the parser. However, this feature is included as of PHP 5.6.0. See this page for more information: http://php.net/migration56.new-features#migration56.new-features.const-scalar-exprs

--------



"The default value must be a constant expression" is misleading (or even wrong).  PHP 5.4.4 fails to parse this function definition:



function htmlspecialchars_latin1($s, $flags = ENT_COMPAT | ENT_HTML401) {}



This yields a " PHP Parse error:  syntax error, unexpected '|', expecting ')' " although ENT_COMPAT|ENT_HTML401 is certainly what a compiler-affine person would call a "constant expression".



The obvious workaround is to use a single special value ($flags = NULL) as the default, and to set it to the desired value in the function's body (if ($flags === NULL) { $flags = ENT_COMPAT | ENT_HTML401; }).

down

conciseusa at yahoo[nospammm] dot com ¶

9 years ago


With regards to:

It is also possible to force a parameter type using this syntax. I couldn't see it in the documentation.
function foo(myclass par) { }

I think you are referring to Type Hinting. It is documented here: http://ch2.php.net/language.oop5.typehinting

down

ohcc at 163 dot com ¶

1 year ago


As of PHP 5.6, you can use an array as arguments when calling a function with the ... $args syntax.

<?php
    $args = array('wu','WU','wuxiancheng.cn');
    $string = str_replace(...$args);
    echo $string;
?>

Ha ha, is that interesting and powerful? 

Also you can use it like this

<?php
    $args = array('WU','wuxiancheng.cn');
    $string = str_replace('wu', ...$args);
    echo $string;
?>

It also can be used to define a user function.

<?php
    function wxc ($arg1, $arg2, ...$otherArgs){
        echo '<pre>';
        print_r($otherArgs);
        print_r(func_get_args());
        echo '</pre>';
    }
    wxc (1, 2, ...array(3,4,5));
?>

REMEMBER this: ... $args is not supported in PHP 5.5 and older versions.

down

John ¶

10 years ago


This might be documented somewhere OR obvious to most, but when passing an argument by reference (as of PHP 5.04) you can assign a value to an argument variable in the function call. For example:

function my_function($arg1, &$arg2) {
  if ($arg1 == true) {
    $arg2 = true;
  }
}
my_function(true, $arg2 = false);
echo $arg2;

outputs 1 (true)

my_function(false, $arg2 = false);
echo $arg2;

outputs 0 (false)

down

herenvardoREMOVEatSTUFFgmailINdotCAPScom ¶

8 years ago


There is a nice trick to emulate variables/function calls/etc as default values:

<?php
$myVar = "Using a variable as a default value!";

function myFunction($myArgument=null) {
    if($myArgument===null)
        $myArgument = $GLOBALS["myVar"];
    echo $myArgument;
}

// Outputs "Hello World!":
myFunction("Hello World!");
// Outputs "Using a variable as a default value!":
myFunction();
// Outputs the same again:
myFunction(null);
// Outputs "Changing the variable affects the function!":
$myVar = "Changing the variable affects the function!";
myFunction();
?>
In general, you define the default value as null (or whatever constant you like), and then check for that value at the start of the function, computing the actual default if needed, before using the argument for actual work.
Building upon this, it's also easy to provide fallback behaviors when the argument given is not valid: simply put a default that is known to be invalid in the prototype, and then check for general validity instead of a specific value: if the argument is not valid (either not given, so the default is used, or an invalid value was given), the function computes a (valid) default to use.

down

nate at natemurray dot com ¶

11 years ago


Of course you can fake a global variable for a default argument by something like this:
<?php
function self_url($text, $page, $per_page = NULL) {
  $per_page = ($per_page == NULL) ? $GLOBALS['gPER_PAGE'] : $per_page; # setup a default value of per page
  return sprintf("<a href=%s?page=%s&perpage=%s>%s</a>", $_SERVER["PHP_SELF"], $page, $per_page, $text);
}
?>

down

ksamvel at gmail dot com ¶

11 years ago


by default Classes constructor does not have any arguments. Using small trick with func_get_args() and other relative functions constructor becomes a function w/ args (tested in php 5.1.2). Check it out:

class A {
    public function __construct() {
        echo func_num_args() . "<br>";
        var_dump( func_get_args());
        echo "<br>";
    }
}

$oA = new A();
$oA = new A( 1, 2, 3, "txt");

Output:

0
array(0) { }
4
array(4) { [0]=> int(1) [1]=> int(2) [2]=> int(3) [3]=> string(3) "txt" }

down

jcaplan at bogus dot amazon dot com ¶

10 years ago


In function calls, PHP clearly distinguishes between missing arguments and present but empty arguments.  Thus:

<?php
function f( $x = 4 ) { echo $x . "\\n"; }
f(); // prints 4
f( null ); // prints blank line
f( $y ); // $y undefined, prints blank line
?>

The utility of the optional argument feature is thus somewhat diminished.  Suppose you want to call the function f many times from function g, allowing the caller of g to specify if f should be called with a specific value or with its default value:

<?php
function f( $x = 4 ) {echo $x . "\\n"; }

// option 1: cut and paste the default value from f's interface into g's
function g( $x = 4 ) { f( $x ); f( $x ); }

// option 2: branch based on input to g
function g( $x = null ) { if ( !isset( $x ) ) { f(); f() } else { f( $x ); f( $x ); } }
?>

Both options suck.

The best approach, it seems to me, is to always use a sentinel like null as the default value of an optional argument.  This way, callers like g and g's clients have many options, and furthermore, callers always know how to omit arguments so they can omit one in the middle of the parameter list.

<?php
function f( $x = null ) { if ( !isset( $x ) ) $x = 4; echo $x . "\\n"; }

function g( $x = null ) { f( $x ); f( $x ); }

f(); // prints 4
f( null ); // prints 4
f( $y ); // $y undefined, prints 4
g(); // prints 4 twice
g( null ); // prints 4 twice
g( 5 ); // prints 5 twice

?>

down

rburnap at intelligent dash imaging dot com ¶

6 years ago


This may be helpful when you need to call an arbitrary function known only at runtime:

You can call a function as a variable name.
<?php

function foo(){
    echo"\nfoo()";
}

function callfunc($x, $y = '')
{
    if( $y=='' )
    {
        if( $x=='' )
             echo "\nempty";
        else $x();
    }
    else
         $y->$x();
}

class cbar {
    public function fcatch(){ echo "\nfcatch"; }
}

$x = '';
callfunc($x);
$x = 'foo';
callfunc($x);
$o = new cbar();
$x = 'fcatch';
callfunc($x, $o);
echo "\n\n";
?>

The code will output

empty
foo()
fcatch

down

thesibster at hotmail dot com ¶

13 years ago


Call-time pass-by-ref arguments are deprecated and may not be supported later, so doing this:

----
function foo($str) {
    $str = "bar";
}

$mystr = "hello world";
foo(&$mystr);
----

will produce a warning when using the recommended php.ini file.  The way I ended up using for optional pass-by-ref args is to just pass an unused variable when you don't want to use the resulting parameter value:

----
function foo(&$str) {
    $str = "bar";
}

foo($_unused_);
----

Note that trying to pass a value of NULL will produce an error.

down

mracky at pacbell dot net ¶

6 years ago


Nothing was written here about argument types as part of the function definition.

When working with classes, the class name can be used as argument type.  This acts as a reminder to the user of the class, as well as a prototype for php  control. (At least in php 5 -- did not check 4).

<?php
class foo {
  public $data;
  public function __construct($dd)
  {
    $this->data = $dd;
  }
};

class test {
  public $bar;

  public function __construct(foo $arg) // Strict typing for argument
  {
    $this->bar = $arg;
  }
  public function dump()
  {
    echo $this->bar->data . "\n";
  }

};

$A = new foo(25);
$Test1 = new test($A);
$Test1->dump();
$Test2 = new test(10); // wrong argument for testing

?>
outputs:
25
PHP Fatal error:  Argument 1 passed to test::__construct() must be an object of class foo, called in testArgType.php on line 27 and defined in testArgType.php on line 13

down

allankelly at gmail dot com ¶

7 years ago


I like to pass an associative array as an argument. This is reminiscent of a Perl technique and can be tested with is_array. For example:
<?php
function div( $opt )
{
    $class = '';
    $text  = '';
    if( is_array( $opt ) )
    {
        foreach( $opt as $k => $v )
        {
            switch( $k )
            {
                case 'class': $class = "class = '$v'";
                                 break;
                case 'text': $text = $v;
                                 break;
            }
        }
    }
    else
    {
        $text = $opt;
    }
    return "<div $class>$text</div>";
}
?>

down

g dot sokol99 at g-sokol dot info ¶

21 days ago


Nullable arguments:

<?php

class C {}

function foo(?C $a)
{
    var_dump($a);
}

foo(null);

foo();
?>

Output:

NULL
PHP Warning:  Uncaught ArgumentCountError: Too few arguments to function foo(), 0 passed in php shell code on line 1 and exactly 1 expected in php shell code:1
Stack trace:
#0 php shell code(1): foo()
#1 {main}
  thrown in php shell code on line 1

Usage of "?" Is also possible with "string", "int", "array" and so on primitive types (which is strange). Also unliKe "= null" "?" can be passed not only for tail of arguments, e.g.:
<?php
function foo(?string $a, string $b) {}
?>

down

catman at esteticas dot se ¶

1 year ago


I wondered if variable length argument lists and references works together, and what the syntax might be. It is not mentioned explicitly yet in the php manual as far as I can find. But other sources mention the following syntax "&...$variable" that works in php  5.6.16. 

<?php
function foo(&...$args)
{
    $i = 0;
    foreach ($args as &$arg) {
        $arg = ++$i;
    }
}
foo($a, $b, $c);
echo 'a = ', $a, ', b = ', $b, ', c = ', $c;
?>
Gives
a = 1, b = 2, c = 3

down

wls at wwco dot com ¶

15 years ago


Follow up to resource passing:



It appears that if you have defined the resource in the same file

as the function that uses it, you can get away with the global trick.



Here's the failure case:



  include "functions_doing_globals.php"

  $conn = openDatabaseConnection();

  invoke_function_doing_global_conn();



...that it fails.



Perhaps it's some strange scoping problem with include/require, or

globals trying to resolve before the variable is defined, rather

than at function execution.

down

-1

aasasdasdf at yandex dot ru ¶

2 years ago


As of PHP 5.5.10, it seems that a variable will be separated from its value if defined right in a function call:

php > error_reporting(E_ALL);
php > function a(&$b) {$b = 1;}
php > a($q = 2); var_dump($q);
Strict Standards: Only variables should be passed by reference in php shell code on line 1
int(2)
php > $w = 3; a($w); var_dump($w);
int(1)

Notice that it's still fine to use a variable that is not defined at all:

php > a($e); var_dump($e);
int(1)

down

-1

ravenswd at gmail dot com ¶

3 years ago


Be careful when passing arguments by reference, it can cause unexpected side-effects if one is not careful.

I had a program designed to sweep through directories and subdirectories and report on the total number of files, and the total size of all files. Since it needed to return two values, I used variables passed by reference.

In one spot in the program, I didn't need the values of those variables after they were returned, so I just used a garbage variable named $ignore instead. This caused a curious bug which took me a while to track down, because the effects of the bug were in a different part of the program than the place where I had made a mistake.

Since the same variable was used for both parameters passed by reference, they ended up both pointing to the same physical location in memory, so changing one of them caused both of them to change. The code below is an excerpt of my program, stripped down to just the few lines necessary to illustrate what was happening:

<?php
sweep ($ignore, $ignore);
// no errors occur here

function sweep ( &$filecount, &$bytecount ) {
  $filecount = 1;
  $bytecount = 1024;
  print "Files: $filecount - Size: $bytecount";  // prints "Files: 1024 - Size: 1024"
}
?>

down

-1

lucas dot ekrause at gmail dot com ¶

2 years ago


In addition to jcaplan@bogus.amazon.com’s comment (http://www.php.net/manual/de/functions.arguments.php#62803) you could also simply write
<?php
function f($x=4){echo $x."\n";}
function g($x=null){for($i=0; $i<2; $i++){call_user_func_array("f", !is_null($x) ? array($x) : array());}}
?>

down

-2

pigiman at gmail dot com ¶

6 years ago


Hey, 



I started to learn for the Zend Certificate exam a few days ago and I got stuck with one unanswered-well question. 

This is the question: 

“Absent any actual need for choosing one method over the other, does passing arrays by value to a read-only function reduce performance compared to passing them by reference?’



This question answered by Zend support team at Zend.com: 



"A copy of the original $array is created within the function scope. Once the function terminates, the scope is removed and the copy of $array with it." (By massimilianoc)



Have a nice day! 



Shaked KO

down

-2

Don dot hosek at gmail dot com ¶

9 years ago


Actually the use of class or global constants does buy us something. It helps enforce the DRY (don't repeat yourself) principle.

down

-2

rwillmann at nocomment dot sk ¶

15 years ago


There is no way how to deal with calling by reference when variable lengths argument list are passed.

<br>Only solutions is to use construction like this:<br>

function foo($args) {<br>

   ...

}



foo(array(&$first, &$second));



Above example pass by value a list of references to other variables :-)



It is courios, becouse when you call a function with arguments passed via &$parameter syntax, func_get_args returns array of copies :-(



rwi

down

-3

coop at better-mouse-trap dot com ¶

16 years ago


If you prefer to use named arguments to your functions (so you don't have to worry about the order of variable argument lists), you can do so PERL style with anonymous arrays:



<?php

function foo($args)

{

    print "named_arg1 : " . $args["named_arg1"] . "\n";

    print "named_arg2 : " . $args["named_arg2"] . "\n";

}



foo(array("named_arg1" => "arg1_value", "named_arg2" => "arg2_value"));

?>



will output:

named_arg1 : arg1_value

named_arg2 : arg2_value

down

-3

keuleu at hotmail dot com ¶

10 years ago


I ran into the problem that jcaplan mentionned. I had just finished building 2 handler classes and one interface. 

During my testing I realized that my handlers were not initializing their variables to their default values when my interface was calling them with 'null' values:

this is a simplified illustration:

<?php

function some_function($v1='value1',$v2='value2',$v3='value3'){
  echo $v1.',  ';
  echo $v2.',  ';
  echo $v3;
}

some_function(); //this will behave as expected, displaying 'value1,  value2,  value3'
some_function(null,null,null); //this on the other hand will display ',  ,' since the variables will take the null value.
?>

I came to about the same conclusion as jcaplan. To force your function parameters to take a default value when a null is passed you need to include a conditionnal assignment inside the function definition. 

<?php
function some_function($v1='value1',$v2='value1',$v3=null){
  $v1=(is_null($v1)?'value1':$v1);
  $v2=(is_null($v2)?'value2':$v2);
  $v3=(is_null($v3)?'value3':$v3);
  echo $v1;
  echo $v2;
  echo $v3;
}
/* 
The default value whether null or an actual value is not so important in the parameter list, what is important is that you include it to allow a default behavior. The default value in the declaration becomes more important at this point:
*/
?>

down

-3

pdenny at magmic dot com ¶

10 years ago


Note that constants can also be used as default argument values
so the following code:

  define('TEST_CONSTANT','Works!');
  function testThis($var=TEST_CONSTANT) {
      echo "Passing constants as default values $var";
  }
  testThis();

will produce :

Passing constants as default values Works!

(I tried this in both PHP 4 and 5)

down

-1

maduro_0 at hotmail dot com ¶

9 months ago


This will work

function test($a,$b){
    echo 'yes it works';
    echo $a;
    echo $b;
}

echo test('1','2','3','2');

This wouldn't work

function test($a,$b){
    echo 'yes it works';
    echo $a;
    echo $b;
}

echo test('1');

down

-4

guillaume dot goutaudier at eurecom dot fr ¶

14 years ago


Concerning default values for arguments passed by reference:
I often use that trick:
func($ref=$defaultValue) {
    $ref = "new value";
}
func(&$var);
print($var) // echo "new value"

Setting $defaultValue to null enables you to write functions with optional arguments which, if given, are to be modified.

down

-6

Angelina Bell ¶

11 years ago


It is so easy to create a constant that the php novice might do so accidently while attempting to call a function with no arguments.  For example:
<?php
function LogoutUser(){
// destroy the session, the cookie, and the session ID
  blah blah blah;
  return true;
}
function SessionCheck(){
  blah blah blah;
// check for session timeout
...
    if ($timeout) LogoutUser;  // should be LogoutUser();
}
?>

OOPS!  I don't notice my typo, the SessionCheck function
doesn't work, and it takes me all afternoon to figure out why not!

<?php
LogoutUser;
print "new constant LogoutUser is " . LogoutUser;
?>

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-7

grinslives13 at hotmail dot com~=s/i/ee/g ¶

11 years ago


Given that we have two coding styles:

#
# Code (A)
#
funtion foo_a (&$var)
{
    $var *= 2;
    return $var;
}
foo_a($a);

#
# Code (B)
#
function foo_b ($var)
{
    $var *= 2;
    return $var;
}
foo_b(&$a);

I personally wouldn't recommend (B) - I think it strange why php would support such a convention as it would have violated foo_b's design - its use would not do justice to its function prototype. And thinking about such use, I might have to think about copying all variables instead of working directly on them... 

Coding that respects function prototypes strictly would, I believe, result in code that is more intuitive to read. Of course, in php <=4, not being able to use default values with references, we can't do this that we can do in C:

#
# optional return-value parameters
#
int foo_c (int var, int *ret)
{
    var *= 2;
    if (ret) *ret = var;
    return var;
}
foo_c(2, NULL);

Of course, since variables are "free" anyway, we can always get away with it by using dummy variables...

zlel

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-5

artiebob at go dot com ¶

15 years ago


here is the code to pass a user defined function as an argument.  Just like in the usort method.



<?php

func2("func1");

function func1 ($arg){

        print ("Hello $arg");        

}

function func2 ($arg1){         

        $arg1("World");  //Does the same thing as the next line

        call_user_func ($arg1, "World");

}

?>

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-9

jacob at jacobweber dot com ¶

5 years ago


This page states:

"Note that when using default arguments, any defaults should be on the right side of any non-default arguments; otherwise, things will not work as expected."

There seems to be one exception to this. Say you're using type-hinting for an argument, but you want to allow it to be NULL, and you want additional required arguments to the right of it. PHP allows this, as long as you give it the type-hinted argument a default value of NULL. For example:

<?php
function sample(ClassA $a = NULL, $b) {
}
sample(new ClassA(), ''); // success
sample(new ClassB(), ''); // failure; wrong type
sample(NULL, ''); // success
sample(new ClassA()); // failure; missing second argument
?>

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-7

csaba at alum dot mit dot edu ¶

12 years ago


Argument evaluation left to right means that you can save yourself a temporary variable in the example below whereas $current = $prior + ($prior=$current) is just the same as $current *= 2;

function Sum() { return array_sum(func_get_args()); }
function Fib($n,$current=1,$prior=0) {
    for (;--$n;) $current = Sum($prior,$prior=$current);
    return $current;
}

Csaba Gabor
PS.  You could, of course, just use array_sum(array(...)) in place of Sum(...)

down

-9

heck AT fas DOT harvard DOT edu ¶

12 years ago


I have some functions that I'd like to be able to pass arguments two ways: Either as an argument list of variable length (e.g. func(1, 2, 3, 4)) or as an array (e.g., func(array(1,2,3,4)). Only the latter can be constructed on the fly (e.g., func($ar)), but the syntax of the former can be neater. 

The way to do it is to begin the function as follows:
  $args = func_get_args();
  if (is_array ($args[0]))
    $args = $args[0];
Then one can just use $args as the list of arguments.

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-5

d_maley at hotmail dot com ¶

1 year ago


If you define your functions in the following way, you can call them whilst only specifying the default parameters you need

1. Define your function with its mandatory parameters, and an optional array

2. Declare your optional parameters as local variables

3. The crux: replace the value of any optional parameters that you have passed via the array, using PHP's facility to interpret variable variable names. This line is identical for every function

4. Call the function, passing its mandatory parameters, and only those optional parameters that you require

For example,

function test_params($a, $b, $arrOptionalParams = array()) {
  $c = 'sat';
  $d = 'mat';
  foreach($arrOptionalParams as $key => $value) ${$key} = $value;
  echo "$a $b $c on the $d";
}

and then call it like this

test_params('The', 'dog', array('c' => 'stood', 'd' => 'donkey'));
test_params('The', 'cat', array('d' => 'donkey'));
test_params('A', 'dog', array('c' => 'stood'));

Results:

The dog stood on the donkey
The cat sat on the donkey
A dog stood on the mat

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-7

balint , at ./ atres &*( ath !# cx ¶

11 years ago


(in reply to benk at NOSPAM dot icarz dot com / 24-Jun-2005 04:21)
I could make use of this assignment, as below, to have a permanently existing, but changing data block (because it is used by many other classes), where the order or the refreshed contents are needed for the others: (DB init done by one, an other changed the DB, and thereafter all others need to use the other DB without creating new instances, or creating a log array in one, and we would like to append the new debug strings to the array, atmany places.)

class xyz {
    var argN = array();
    function xyz($argN) {
        $this->argN = &$argN;
    }
    function etc($text) {
        array_push($this->argN, $text);
    }
}
class abc {
    var argM = array();
    function abc($argM) {
        $this->argM = &$argM;
    }
    function etc($text) {
        array_push($this->argM, $text);
    }
}

$messages=array("one", "two");
$x = new xyz(&$messages);
$x->etc("test");

$a = new abc(&$messages);
$a->etc("tset");

...

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-8

rich at richware dot net ¶

1 year ago


How to pass a class as an argument? This is simple:

<?php
class TMath {
    private $_Total;
    function Sum() {
        $this->_Total = 0;
        foreach (func_get_args() as $n) {
            $this->_Total += $n;
        }
    }
    function Total() {
        return $this->_Total;
    }
}
    $myMath = new TMath();
    $myMath->Sum(1,2,3);
    ShowTotal($myMath);

    function ShowTotal($aMath) {
        echo $aMath->Total().'<br/>';
    }

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-14

post at auge8472 dot de ¶

3 years ago


I needed a way to decide between two possible values for one function parameter. I didn't want to decide it before calling the function but wanted to do the constraint inside the function call.

$foo = 1;
$bar = 2;

function foobar($val) {
    echo $val;
    }

foobar(isset($foo) ? $foo : $bar);

// output: 1

$bar = 2;

function foobar($val) {
    echo $val;
    }

foobar(isset($foo) ? $foo : $bar);

// output: 2

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