Reference and Manual

Hosting Glossary PHP HTML 4.01 CSS 2.0 Core Javascript 1.5 XHTML 1.0

Type Juggling

PHP Manual
Prev	Chapter 10. Types	Next

Type Juggling

PHP does not require (or support) explicit type definition in variable declaration; a variable's type is determined by the context in which that variable is used. That is to say, if you assign a string value to variable $var, $var becomes a string. If you then assign an integer value to $var, it becomes an integer.

An example of PHP's automatic type conversion is the addition operator '+'. If any of the operands is a float, then all operands are evaluated as floats, and the result will be a float. Otherwise, the operands will be interpreted as integers, and the result will also be an integer. Note that this does NOT change the types of the operands themselves; the only change is in how the operands are evaluated.


<?php
$foo = "0";  // $foo is string (ASCII 48)
$foo += 2;   // $foo is now an integer (2)
$foo = $foo + 1.3;  // $foo is now a float (3.3)
$foo = 5 + "10 Little Piggies"; // $foo is integer (15)
$foo = 5 + "10 Small Pigs";     // $foo is integer (15)
?>

If the last two examples above seem odd, see String conversion to numbers.

If you wish to force a variable to be evaluated as a certain type, see the section on Type casting. If you wish to change the type of a variable, see settype().

If you would like to test any of the examples in this section, you can use the var_dump() function.

Note: The behaviour of an automatic conversion to array is currently undefined.

<?php $a = "1"; // $a is a string $a[0] = "f"; // What about string offsets? What happens? ?>

Since PHP (for historical reasons) supports indexing into strings via offsets using the same syntax as array indexing, the example above leads to a problem: should $a become an array with its first element being "f", or should "f" become the first character of the string $a?
The current versions of PHP interpret the second assignment as a string offset identification, so $a becomes "f", the result of this automatic conversion however should be considered undefined. PHP 4 introduced the new curly bracket syntax to access characters in string, use this syntax instead of the one presented above:
<?php $a = "abc"; // $a is a string $a{1} = "f"; // $a is now "afc" ?>
See the section titled String access by character for more information.

Type Casting

Type casting in PHP works much as it does in C: the name of the desired type is written in parentheses before the variable which is to be cast.


<?php
$foo = 10;   // $foo is an integer
$bar = (boolean) $foo;   // $bar is a boolean
?>

The casts allowed are:

(int), (integer) - cast to integer
(bool), (boolean) - cast to boolean
(float), (double), (real) - cast to float
(string) - cast to string
(array) - cast to array
(object) - cast to object

Note that tabs and spaces are allowed inside the parentheses, so the following are functionally equivalent:


<?php
$foo = (int) $bar;
$foo = ( int ) $bar;
?>

Note: Instead of casting a variable to string, you can also enclose the variable in double quotes.
<?php $foo = 10; // $foo is an integer $str = "$foo"; // $str is a string $fst = (string) $foo; // $fst is also a string // This prints out that "they are the same" if ($fst === $str) { echo "they are the same"; } ?>

It may not be obvious exactly what will happen when casting between certain types. For more info, see these sections:

Prev	Home	Next
Pseudo-types used in this documentation	Up	Variables

Web Hosting Showcase View the web hosting showcase to find more relevant web hosting choice that will guide you in selecting a good web hosting company.
	Cheap Web Hosting	ASP & ASP.Net Hosting	Dedicated Servers
	Windows 2000 & 2003 Server Hosting	Ecommerce Hosting	PHP Hosting
	Linux & Unix Hosting	Cold Fusion Hosting	South America
	Europe	Reseller Hosting	Managed Hosting
	Virtual Private Server	Asia Pacific

Web Hosting and Development Tools

Network Tools Download Template Programming Manuals Developer Tools

•	HostForWeb HostForWeb.com
	20GB Transfer, Unlimited Subdomans & E-mails, Smaller package 200MB - $9.95
•	ApolloHosting - Fast & Reliable Web Site Hosting Apollo Hosting
	Cnet User Recommended - Cnet Certified
•	HostwayVPS Hostway Corporation
	Dedicated server performance, at a fraction of normal dedicated server prices
•	Looking for dedicated servers in the U.K. ? Xilo
	XILO can provide dedicated servers with serveral different configurations.
•	SingleHop SingleHopSingleHop
	Intel Pentium D 945 with 1GB Ram, 320Gb hard disk & 2500Gb bandwidth at US$159 per month

	Whois Search Speed Test Top 25 Hosts Hosting Reviews 100 Hosts
Dedicated servers & web hosting directory

Dedicated servers & web hosting directory

Dedicated Server

Reference and Manual

Type Juggling

Type Casting

Dedicated servers
& web hosting directory