Php function default argument value

PHP Functions

PHP has more than 1000 built-in functions, and in addition you can create your own custom functions.

PHP Built-in Functions

PHP has over 1000 built-in functions that can be called directly, from within a script, to perform a specific task.

Please check out our PHP reference for a complete overview of the PHP built-in functions.

PHP User Defined Functions

Besides the built-in PHP functions, it is possible to create your own functions.

• A function is a block of statements that can be used repeatedly in a program.
• A function will not execute automatically when a page loads.
• A function will be executed by a call to the function.

Create a User Defined Function in PHP

A user-defined function declaration starts with the word function :

Syntax

Note: A function name must start with a letter or an underscore. Function names are NOT case-sensitive.

Tip: Give the function a name that reflects what the function does!

In the example below, we create a function named «writeMsg()». The opening curly brace ( < ) indicates the beginning of the function code, and the closing curly brace ( >) indicates the end of the function. The function outputs «Hello world!». To call the function, just write its name followed by brackets ():

Example

writeMsg(); // call the function
?>

PHP Function Arguments

Information can be passed to functions through arguments. An argument is just like a variable.

Arguments are specified after the function name, inside the parentheses. You can add as many arguments as you want, just separate them with a comma.

The following example has a function with one argument ($fname). When the familyName() function is called, we also pass along a name (e.g. Jani), and the name is used inside the function, which outputs several different first names, but an equal last name:

Example

familyName(«Jani»);
familyName(«Hege»);
familyName(«Stale»);
familyName(«Kai Jim»);
familyName(«Borge»);
?>

The following example has a function with two arguments ($fname and $year):

Example

function familyName($fname, $year) echo «$fname Refsnes. Born in $year
«;
>

familyName(«Hege», «1975»);
familyName(«Stale», «1978»);
familyName(«Kai Jim», «1983»);
?>

PHP is a Loosely Typed Language

In the example above, notice that we did not have to tell PHP which data type the variable is.

PHP automatically associates a data type to the variable, depending on its value. Since the data types are not set in a strict sense, you can do things like adding a string to an integer without causing an error.

In PHP 7, type declarations were added. This gives us an option to specify the expected data type when declaring a function, and by adding the strict declaration, it will throw a «Fatal Error» if the data type mismatches.

In the following example we try to send both a number and a string to the function without using strict :

Example

function addNumbers(int $a, int $b) return $a + $b;
>
echo addNumbers(5, «5 days»);
// since strict is NOT enabled «5 days» is changed to int(5), and it will return 10
?>

To specify strict we need to set declare(strict_types=1); . This must be on the very first line of the PHP file.

In the following example we try to send both a number and a string to the function, but here we have added the strict declaration:

Example

function addNumbers(int $a, int $b) return $a + $b;
>
echo addNumbers(5, «5 days»);
// since strict is enabled and «5 days» is not an integer, an error will be thrown
?>

The strict declaration forces things to be used in the intended way.

PHP Default Argument Value

The following example shows how to use a default parameter. If we call the function setHeight() without arguments it takes the default value as argument:

Example

setHeight(350);
setHeight(); // will use the default value of 50
setHeight(135);
setHeight(80);
?>

PHP Functions — Returning values

To let a function return a value, use the return statement:

Example

PHP Return Type Declarations

PHP 7 also supports Type Declarations for the return statement. Like with the type declaration for function arguments, by enabling the strict requirement, it will throw a «Fatal Error» on a type mismatch.

To declare a type for the function return, add a colon ( : ) and the type right before the opening curly ( < )bracket when declaring the function.

In the following example we specify the return type for the function:

Example

You can specify a different return type, than the argument types, but make sure the return is the correct type:

Example

Passing Arguments by Reference

In PHP, arguments are usually passed by value, which means that a copy of the value is used in the function and the variable that was passed into the function cannot be changed.

When a function argument is passed by reference, changes to the argument also change the variable that was passed in. To turn a function argument into a reference, the & operator is used:

Example

Use a pass-by-reference argument to update a variable:

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Php function default argument value

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

#!/usr/bin/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

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)

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».
*/
?>

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PHP Default Parameters

Summary: in this tutorial, you’ll learn about PHP default parameters and default parameters to simplify the function calls.

Introduction to the PHP default parameters

The following defines the concat() function that concatenates two strings with a delimiter:

 function concat($str1, $str2, $delimiter) < return $str1 . $delimiter . $str2; >Code language: HTML, XML (xml)

When you call the concat() function, you need to pass exactly three arguments. For example:

 function concat($str1, $str2, $delimiter) < return $str1 . $delimiter . $str2; > $message = concat('Hi', 'there!', ' '); echo $message;Code language: HTML, XML (xml)

However, you’ll find that you often use the space ‘ ‘ as the delimiter. And it’s repetitive to pass the space whenever you call the function.

This is why default parameters come into play.

PHP allows you to specify a default argument for a parameter. For example:

 function concat($str1, $str2, $delimiter = ' ') < return $str1 . $delimiter . $str2; >Code language: HTML, XML (xml)

In this example, the $delimiter parameter takes the space as the default argument.

When you call the concat() function and don’t pass the delimiter argument, the function will use the space for the $delimiter like this:

 function concat($str1, $str2, $delimiter = ' ') < return $str1 . $delimiter . $str2; > $message = concat('Hi', 'there!'); echo $message;Code language: HTML, XML (xml)

However, if you pass an argument for the $delimiter , the function will use that argument instead:

 function concat($str1, $str2, $delimiter = ' ') < return $str1 . $delimiter . $str2; > $message = concat('Hi', 'there!', ','); echo $message;Code language: HTML, XML (xml)

In this example, we passed a comma to the $delimiter . The concat() function used the comma ( , ) instead of the default argument.

When you specify a default argument for a parameter, the parameter becomes optional. It means that you can pass a value or skip it.

Default arguments

The default arguments must be constant expressions. They cannot be variables or function calls.

PHP allows you to use a scalar value, an array, and null as the default arguments.

The order of default parameters

When you use default parameters, it’s a good practice to place them after the parameters that don’t have default values. Otherwise, you will get unexpected behavior. For example:

 function concat($delimiter = ' ', $str1, $str2) < return $str1 . $delimiter . $str2; > $message = concat('Hi', 'there!', ','); echo $message; Code language: HTML, XML (xml)

Summary

• Use default parameters to simplify the function calls.
• Default parameters are optional.

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