Related Articles

Introduction to PHP

PHP Basic Syntax

Basics of PHP Variables with
Security Concerns

PHP Conditional Statements

Boolean Logic for PHP

Boolean Logic and PHP
Conditions with Security
Concerns

PHP Function Basics and
Security Issues

PHP Operator Basics with
Security Concerns

PHP Loop Statements

PHP Array Basics with Security
Concerns

PHP Variabne(Rcg0E$casácz/@>

Basia{8N"(PHP Referenge,-i>+p>=p¤Chásq='navg`sUZlm<''>qHP Fklm!Han$liOfæáãybs¤a~d|js>Æasic SeGuâ{ty

&nbóð{zm@<¤

e (reG="htôp:m/sWg¬rrocd-oMpkrKngom/index.htm">Broee0Èetwosk¸/a><|h&c|css="nav>¼q!höef=¢ht6p://www.broad-netwnr­.kËm?-ember>h%eæ6BeccmU&a Member<p¾� <2 class="nav"<å
href"èdtp://ww.fòad-netwkrû¬c--/Knntacp.xvm".C/ftaqtt"a./ô<ô(cLess=aní">a`irÀ$=*Http:/.÷òwèbrnaà-netwkr{,com/aerMdýu.|.htm >AæRa'ment � <#rticèd0¥d#A1' {tYhd=ÃdéBpla};yèliîe- lock; Uyèp¸/"V33 rebvibeè=clhgê:top'>� % ´" inbgE7{io.StNrage.writerLoeifa-=A*Noïxn") $ 0" { ¤ `
( d document.getElementById('SPW').style.display = "inline"; } sessionStorage.writerID = "2"; sessionStorage.articleID = "330"; sessionStorage.partNo = "11"; //ajax var xmlhttp; var currentURL = document.URL; if (window.XMLHttpRequest) {// code for IE7+, Firefox, Chrome, Opera, Safari xmlhttp = new XMLHttpRequest(); } else {// code for IE6, IE5 xmlhttp = new ActiveXObject('Microsoft.XMLHTTP'); } xmlhttp.onreadystatechange=function() { if (xmlhttp.readyState == 4) { if (xmlhttp.status == 200) { } else { } } } writerID = sessionStorage.writerID; articleID = sessionStorage.articleID; partNo = sessionStorage.partNo; readerID = sessionStorage.readerID; sendStr = 'writerID='+writerID+'&articleID='+articleID+'&partNo='+partNo+'&readerID='+readerID+'&articleURL='+currentURL; xmlhttp.open('post', 'http://www.broad-network.com/pageViews.php', true); xmlhttp.setRequestHeader('Content-type', 'application/x-www-form-urlencoded'); xmlhttp.send(sendStr); document.getElementById('edit').href = "http://www.broad-network.com/edit.php?writerID=2&articleID=330&partNo=11";

PHP Variable Scope Basics

PHP Array Basics with Security Concerns - Part 11

Foreword: In this part of the series, I give you the basics of what is known as PHP variable scope.

By: Chrysanthus Date Published: 18 Jan 2018

Introduction

This is part 11 of my series, PHP Array Basics with Security Concerns. In this part of the series, I give you the basics of what is known as PHP variable scope. A block is a set of statements enclosed in curly braces, which are { and }. The question here is: if a variable is declared outside a block, will it be seen in the block? On the other hand, if it is declared inside the block, will it be seen outside the block? Blocks do not occur arbitrarily in code. There are certain constructs that have blocks.  The following constructs have blocks: if, for, and function. You should have seen these constructs (statements).

For the rest of this tutorial, we look at the if, for and function constructs and how variable scope is applied to them. Some code samples below, may not work; do not worry about that.

The if Construct and Variable Scope
Read and try the following code:

    <?php

        $hisVar = "his stuff";

        if (25 == 25)
            {
                    echo ($hisVar);
                $herVar = "her stuff";
            }

        //echo($herVar);

    ?>

The if condition is if 25 equals 25. Now this condition will always return true, and so the if block will always be executed. Outside the if-block, the variable, $hisVar is declared and assigned the value, "his stuff". Inside the if-block there is a statement to print $hisVar at the web page. This variable was declared outside the block; if it should be seen inside the block, it will be printed (displayed). If you tried the code you would have noticed that the value of $hisVar was printed (seen inside the block).

Now, inside the block, a new variable, $herVar is declared and has a value assigned to it. Outside the block, there is a comment. This comment is actually a statement preceded by the comment denotation, //. Because of this preceding sign, the statement is not executed. If you remove the comment and re-try the code, the following explanation will follow:

The $herVar variable is declared inside the block. Now, if it should be seen outside the block, then the last statement (with the comment denotation, removed) would print its value. Remove the // symbol and try the code and note that the last write statement would work, and you would see “her stuff” printed (on the same line in the web page).

So, a variable declared outside the if-block is seen inside the if-block; a variable declared inside the if-block is also seen outside the if-block. Also note that a variable declared outside the if-block is also seen in the if-condition (parentheses).

The for Construct and Variable Scope
The following code has been written similar to the above; the variables and test (echo) statements have been written in a similar way.

Try the code:

    <?php

        $hisVar = "his stuff";

        for ($i=0; $i< 3; ++$i)
            {
                echo ($hisVar);
                $herVar = "her stuff";
            }

        //echo($herVar);
        //echo($i);

    ?>

You should have tried the code. Note that the variable declared outside the for-block is seen inside the for-block. In this case the value of the variable is printed 3 times (on the same line).

Now remove the comment denotation in the last-but-one line and try the code again; the value of the variable, $herVar, is printed (still on the same line). This is because a variable declared inside the for-block is seen outside the for-block (and vice-versa).

Remove the comment symbol from the very last line of the above script code. If the variable, that has been declared in the for-loop parentheses, can be seen outside the for-construct (loop), then the last statement (line) will display it. Try the code (with the last comment symbol removed) and note that the variable is seen outside the for-construct.

Now, a variable declared outside the for-block is seen inside the for-block; a variable declared inside the for-block is seen outside the for-block, as demonstrated above. A variable declared outside the for-construct is seen inside the for-loop parentheses; a variable declared inside the for-loop parentheses is seen outside the for-construct (the value of 3 is printed above).
This remark is applicable to while-loops as well.

The Function Construct and Variable Scope
The following code has been written similar to the above; the variables and test (print) statements have been written in a similar way.

Read and try the code:

    <?php

        $myVar = "my stuff";
        $hisVar = "his stuff";

        function myFn($aVar=$myVar)
            {
                echo($aVar);
                echo($hisVar);
                $herVar = "her stuff";
            }

        myFn();

        //echo($herVar);

    ?>

You should have tried the code. Note that a variable declared outside the function-block is NOT seen inside the function-block. Also, a variable declared outside the function construct can NOT be seen inside the function parentheses (you will verify that on your own).

Now remove the comment denotation in the last line and try the code again; notice that a variable ($herVar) declared inside a function block can NOT be seen outside the function block.

The global Keyword
You can make a variable declared outside the function construct to be seen inside the function block by using the global keyword, as in the following code:

    <?php

        $myVar = "my stuff";
        $hisVar = "his stuff";

        function myFn()
            {
                global $myVar, $hisVar;

                echo($hisVar);
            }

        myFn();

    ?>

The global statement is typed at the top of the function block (inside). Try the code and note that a variable declared outside the function construct is seen inside the function block with the help of the global statement. The global statement can take more than one variable.

Summary
With the exception of the function definition, a variable declared outside a block is seen inside the block and vice-versa. To make a variable declared outside a function block to be seen inside the function block, you have to use the global statement inside the function block.

That is it for this part of the series. We stop here and continue in the next part.

Chrys

Related Links

Basics of PHP with Security Considerations
More Related Links
Pure PHP Mailsend - sendmail
PurePHP MySQL API
Using the PurePHP MySQL API
Cousins
JavaScript/ECMAScript Course
Perl Course

BACK NEXT

Comments

Submit Comment

Become the Writer's Follower
Send the Writer a Message