PHP 7 Functions
The real power of PHP comes from its functions; it has more than 1000 built-in functions.
PHP User Defined Functions
Besides the built-in PHP functions, we can create our own functions.
A function is a block of statements that can be used repeatedly in a program.
A function will not execute immediately 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
function functionName()
{
code to be executed;
}
Note: A function name can start with a letter or underscore (not a number).
Tip: Give the function a name that reflects what the function does!
Function names are NOT case-sensitive.
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
<?php
function writeMsg() {
echo "Hello world!";
}
writeMsg(); // call the function
?>
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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 ($fname). When the familyName() function is called, we also pass along a name (e.g. Jani), and the name is used inside the function, which outputs several different first names, but an equal last name:
Example
<?php
function familyName($fname) {
echo "$fname Refsnes.<br>";
}
familyName("Jani");
familyName("Hege");
familyName("Stale");
familyName("Kai Jim");
familyName("Borge");
?>
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The following example has a function with two arguments ($fname and $year):
Example
<?php
function familyName($fname, $year) {
echo "$fname Refsnes. Born in $year <br>";
}
familyName("Hege", "1975");
familyName("Stale", "1978");
familyName("Kai Jim", "1983");
?>
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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 and error.
In PHP 7, type declarations were added. This gives us an option to specify the data type expected when declaring a function, and by enabling the strict requirement, it will throw a "Fatal Error" on a type mismatch.
In the following example we try to add a number and a string with
without the strict requirement:
Example
<?php
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
?>
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In the following example we try to add a number and a string with
with the strict requirement:
Example
<?php declare(strict_types=1); // strict requirement
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
?>
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To specify strict we need to set declare(strict_types=1);.
This must be the on the very first line of the PHP file. Declaring strict
specifies that function calls made in that file must strictly adhere to the
specified data types
The strict declaration can make code
easier to read, and it forces things to be used in the intended way.
Going forward in this tutorial, we will use the strict requirement.
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
<?php declare(strict_types=1); // strict requirement
function setHeight(int $minheight = 50) {
echo "The height is : $minheight <br>";
}
setHeight(350);
setHeight(); // will use the default value of 50
setHeight(135);
setHeight(80);
?>
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PHP Functions - Returning values
To let a function return a value, use the return statement:
Example
<?php declare(strict_types=1); // strict requirement
function sum(int $x,
int $y) {
$z = $x + $y;
return $z;
}
echo "5 + 10 = " . sum(5, 10) . "<br>";
echo "7 + 13 = " . sum(7, 13) . "<br>";
echo "2 + 4 = " . sum(2, 4);
?>
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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
<?php declare(strict_types=1); // strict requirement
function addNumbers(float
$a, float $b) : float {
return $a + $b;
}
echo addNumbers(1.2, 5.2);
?>
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You can specify a different return type, than the argument types, but make sure the return is the correct type:
Example
<?php declare(strict_types=1); // strict requirement
function addNumbers(float
$a, float $b) : int {
return (int)($a + $b);
}
echo addNumbers(1.2, 5.2);
?>
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