Zend PHP 5 – Functions – Syntax

7th January 2017

Functions are covered within the Zend PHP study guide. Functions are packages of code that serve as instructions to execute an action.

Any valid PHP code can reside in a function.

You can define a function like the example written below.

<?php
function foo($arg_1, $arg_2, /* ..., */ $arg_n)
{
    echo "Example function.\n";
    return $retval;
}

Functions do not need to be defined before they are referenced, unless a scenario occurs when a function is conditionally defined.

<?php

$makefoo = true;

/* We can't call foo() from here 
   since it doesn't exist yet,
   but we can call bar() */

bar();

if ($makefoo) {
  function foo()
  {
    echo "I don't exist until program execution reaches me.\n";
  }
}

/* Now we can safely call foo()
   since $makefoo evaluated to true */

if ($makefoo) foo();

function bar() 
{
  echo "I exist immediately upon program start.\n";
}

This outputs:

I exist immediately upon program start.
I don't exist until program execution reaches me.

Function names are case-insensitive, though it is usually good form to call functions as they appear in their declaration.

Function parameters and return values are optional, however it is advised to set a default parameter to avoid generating a PHP warning like the following:

<?php
function myFunction($p)
{
    return $p;
}

$x = myFunction("ABC"); // x = "ABC"
$x = myFunction();      // Warning

function myOtherFunction($p = "ABC")
{
    return $p;
}

$x = myOtherFunction("DEF"); // x = "DEF"
$x = myOtherFunction();      // x = "ABC"

PHP comes standard with many in-built functions and constructs. T

here are also functions that require specific PHP extensions compiled in, otherwise fatal “undefined function” errors will appear. For example, the mysqli_connect() function can be used to connect to a database.

Use the phpinfo() or get_loaded_extensions() function which will show the extensions that are loaded into PHP.

Note: This article is based on PHP version 5.5.