Part 3.5Strings in PHP

Strings are sets of ordered characters that make up text. Strings are normally contained within " " or ' '.

The difference between the single quotation mark (or apostrophe) and the double quotation marks (speech marks) is that variables within the single quotation marks (') will not be parsed as variables and will be output directly as they are. In double quotation marks (") the variable will be parsed:

<?php
	$x = 10;
	echo "$x is $x";
	echo "<br />;
	echo '$x is $x';
?>

String tools

Strings can be manipulated in many different ways such as with other programming languages such as Java. For instance, the substring method will get a smaller inner string from within a string. In PHP, there are several generic string methods.

Replace a string inside a string

When a string has text that is to be replaced, str_replace replaces a string within a string and returns it. The following example will replace the word "website" with "dynamic website" within the string specified to it and stores it in $test .

<?php
	$myStr = "Welcome to my website";
	$test = str_replace("website", "dynamic website", $myStr);
?>
		

Get the length of a string

To get the length of some string the strlen function can be used. This takes in a string as a parameter and returns the length of the string.

<?php
	$myStr = "Welcome to my website";
	$test = strlen($myStr);
?>
		

Getting the index of the first occurence of a string

To get the index of the first occurence of a string within a string, the strpos function is used. It is given a parameter of the string to search then the string to search for.

<?php
	$myStr = "Welcome to my website";
	$test = strpos($myStr, "website");
?>
		

In this case, this will return the first index where the word "website" appears.

Getting a substring from a string

A substring is a string within a string. That is means in logic, we can state that A ⊂ B. In PHP we can use the substr function.

To get a substring from the string "My name is Jamie" the substr function can be used to get just my "Jamie". If "Jamie" begins on character 12, then the first letter is on character 11, taking into account Base 0 counting.

<?php
	$myStr = "My name is Jamie";
	$test = substr($myStr, 11, 5);
?>
		

substr takes in three parameters, one which contains the string to substring, one that specifies where to begin the substring from and an optional length. So the last parameter was set to 3 it would return "Jam" rather than "Jamie". The last parameter is optional, so if it is not included it takes from the start to the end.

Encoding a string

MD5 and SHA1 are both string hash algorithms that allow the encoding of a string for use in URLs, order numbers or to store a unique reference in a database or on a web server. Both of these work differently under the hood. Both are shown below.

It is beyond the scope of this article to describe the benefits of MD5 or SHA1, but for the sake of web programming in PHP, it is necessary to know how to store information correctly.

MD5 hashing algorithm

<?php
	$myStr = "My name is Jamie";
	$test = md5($myStr);
?>
		

SHA-1 (Secure Hash Algorithm)

<?php
	$myStr = "My name is Jamie";
	$test = sha1($myStr);
?>
		

Concatenating two strings

Strings are merged together in PHP using the concatenation operator. In Java, this operator is +. In VB.NET this operator is + or &. In PHP the . (full stop) is the concatenation operator.

Two strings can be joined using the following:

<?php
	$test = "My hello world " . " is different to yours.";
?>
		

Getting a character from a string position

Strings are a set of ordered characters. As this is the case it is sometimes necessary to obtain a certain character from such a string. Getting an index from a string is done using the square brackets like this:

<?php
	$myStr = "My name is Jamie";
	$test = $myStr[4];
?>
		

Where the 4 inside the square brackets is the index.