PHPBuilder - Strings & Text in PHP - The ABCs of PHP Part 5

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Strings & Text in PHP - The ABCs of PHP Part 5

by: PHP Builder Staff
April 15, 2009

In the last part of this series we looked at what a variable was in general. Today we'll be covering strings and text. We'll look at the contents those variables would typically hold.
What is a string?
Put simply a string is any sequence of alpha/numeric or punctuation characters enclosed by either a set of "" parentheses or a set of '' parentheses.
Strings are generally used to hold data that we as humans may write down in a sentence or read in a document such as this one, and generally we would not normally perform mathematical calculations on a string. This is not to say however that a string cannot hold a number value, it can. Under normal circumstances however, you would not unless that number was purely for display.
You'll notice also that there are 2 sets of parentheses used to enclose strings mentioned above, each set operates differently to the other.
Using '' parentheses
When you enclose a PHP string using '' (Otherwise know as single quotation marks) exactly what you put in the string is displayed. This means that no embedded variables are translated and no special sequences such as carriage returns are obeyed.
Let me show you an example:

  $variable = 'Hello world';

  Print 'Here is some text [$variable]';

When this is run from the command line the following will be output:
Here is some text [$variable]
Given what we've discussed so far, you might think that this is to be expected, and in a way you would be right, however things are rather different when using the alternate double quote parentheses.
Using "" parentheses
So what's so different about using "" (Otherwise known as double quotation marks), well when we use "" PHP actually interprets the contents of the string. In the case of embedded variable names, these are substituted for the actual contents of the variable, in the case of special escape sequences these are interpreted and replaced with different values as required (More on those in just a moment).
Using the same example as before, let's rewrite it with double quotes instead of single quotes.

  $variable = "Hello world";

  print "Here is some text [$variable]";

This will now output:
Here is some text [Hello world]
PHP's ability to substitute variables directly in a sctring like that is one of it's strongest features, and sometimes a source of frustration to the beginner.
Many PHP beginners assume that because they can insert variables using double quotes, they can also do the same using PHP's built in functions, unfortunately this will not work as expected. EG:
A user trying to use:

  Print "Todays date is date('r')";

May rightfully assume that the result would be:
Todays date is Wed, 25 Mar 2009 13:32:21 +0000
When in actual fact the result will be:
Todays date is date('r')

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