WordPress - Help Reading php Code

WordPress is written in

php
JavaScript
css - StyleSheets
sql - for database access
html
jQuery (a JavaScript library)

You will need to know some of each of these to reverse engineer much of anything. This page deals with php.

I have been programming for a number of years and, basically, I can read almost anything. To write "new" code, I normally just look around, copy something that looks close, and make a few mods. However, I have found WordPress particularly challenging. Normal php is pretty easy (it is almost c-like), but ... well, that is why this page exits.

Basics

echo 'any string';

echo 'a string'.$some_variable.'another string'; // a dot concatenates 2 strings

$var1 .= 'some string'; // concatenate a string to the existing variable

echo writes a string to the "current output" which is the newly created web page. Unfortunately, the "current" web page is frequently replaced with another page before you are able to read your debug messages.

Careful - single and double quotes give different results.

echo 'any string\n';  // this prints the \n without translation
echo "any string\n";  // this converts the \n to a newline character

echo 'a string $some_variable another string'; // this prints exactly what is typed
echo "a string $some_variable another string"; // this replaces $some_variable with the variable's value

String concatenation is always a problem.

Most languages use a plus sign		str1 + str2
VisualBasic uses an ampersand		str1 & str2
php uses a period		$str1 . $str2

As far as I can tell, spaces are never required before or after the period.

All php code is enclosed between tags, any text not between those tags is copied directly to the web page

<?php get_header(); ?> <! get_header()is executed on the server > <h2> Page title </h2> <! this becomes part of the web page >

If you want to stop a function, use return, not exit.

return;   // this works
exit;     // this causes weird problems that are hard to debug

Apparently, all variables start with a dollar sign ($varname)
There is no variable type casting, everything is a variant
classes are supported

Arrays

Arrays have their own rules and a number of functions.

$some_array['any_string'] = 0; // context addressable array (associative array)

// Create an array with 3 elements
$defaults = array('before' => '', 'after' =>  '', 'echo' => true);

// Create an empty array
$defaults = array();

// Operate on each item in the array
foreach ( (array) $keys as $key ) {
  //your code here
}

// Alternate colon syntax
foreach($images as $image):
  echo wp_get_attachment_image($image->ID, 'medium');
endforeach;

// When working with an array of arrays 
foreach ( (array) $keys as $key => $value ) {
  //your code here
  //$key contains the string values of the indices
}

foreach ( (array) array_keys($data) as $field ) { 
  //$field contains the string values of the indices
}

To remove a single element from an array, use the following

unset($data['id']); // not in the array reference

Functions

All functions and classes in PHP have the global scope
Function names are not case-sensitive

function unique_name($parm1, &$parm2, ..., $parmx = 'default'){
  // your code here

  $parm1 = 'abc';     // this will not be seen in the calling code

  $parm2 = 'xyz';     // this will be seen in the calling code

  return $some_value; // another way to return a value (or an array, or an object)
}

By default, all parameters are passed by value (meaning that a copy is passed). If you want to be able to edit the variable, then it must be passed by reference (meaning that you want to pass a pointer). In php, an ampersand (&) indicates that the reference to (address of) the variable is being passed.

The ampersand (&) can be used in either the calling statement, or in the function definition (preferred).

For instance, if you want to be able to edit an array's contents, then it must be passed by reference.

    $book_info = array(); // create an empty array

    $this->set_array( $book_info, $form_data, 'title'); // passed by value, changes are lost

    $this->set_array(&$book_info, $form_data, 'title'); // passed by reference, changes are available in calling routine

  function set_array($an_array, $source, $field){
    $an_array[$field]  = !isset($source['lib_events_'.$field])? NULL : $source['lib_events_'.$field];
  }

Additional info: Function arguments Returning values

WordPress specific conventions

There are a few very confusing commands used everywhere. After a while, I discovered that they are a part of the WordPress library.

wp-includes/l10n.php   the WordPress Translation API

These functions translate the text into the appropriate language.

// this does a simple translate and echo <h2><?php _e('Not Found','atahualpa'); ?></h2> // The following first translates - using __(xx) - the displayed part of the text and // then adds the link info - using printf(xx) - that must not be translated // The "%s" is replaced with the link <p><?php printf(__('You must be %slogged in</a> to post a comment.', 'atahualpa'), '<a href="' . get_option('siteurl') . '/wp-login.php?redirect_to=' . urlencode(get_permalink()) . '">')?></p>

These are how the functions are implemented

function __( $text, $domain = 'default' ) {
  return translate( $text, $domain );
}

function _e( $text, $domain = 'default' ) {
  echo translate( $text, $domain );
}

There are a lot more, but these are the ones I saw everywhere.

* if * statements

Most of the php code I've seen uses standard c-syntax for if statements.

if ( false == $last_bar )                // simple if..else
  return $string;
else
  return substr( $string, 0, $last_bar );

While that works, I suggest ALWAYS using the block format.

if ( false == $last_bar ){                // the curly braces define blocks
  return $string;
} else {
  return substr( $string, 0, $last_bar );
}

Either else if () or elseif () can be used.

Some files use an alternate colon syntax (instead of curly braces)

if ('open' == $post->comment_status) :

  //your code here

else :

  //your code here

endif;

This immediate or in-line syntax is also used a lot - a value is returned based on the conditional statement (inside the parentheses). The first element is returned (or executed) if the condition is true, otherwise the second element is returned.

(a>5) ? 'good' : 'bad';               // return one of the strings

(a>5) ? function_1() : function_2();  // call one of the functions

Objects

In most of the code I've seen, all the function names are global. However, objects allow you to encapsulate those and leave only the instance name as a global.

class xyz_unique {

  function xyz_unique() {  // class constructor
    // code goes here
  }

  function any_name() {  // member function (method), name is only class unique
    // code goes here
  }

} // end of class definition

$xyz_unique = new xyz_unique();  // creates an instance and executes the constructor

class WP_Scripts extends WP_Dependencies { // how to inherit from a base class
}

In most object oriented languages, the member methods can call each other without any special syntax. However, php requires $this->

any_name();          // fails, function not found
$this->any_name();   // works

When calling a member function from outside the instance, use

$xyz_unique->any_name();   // instance_name->member_name();

Author: Robert Clemenzi