PHP Manual
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Chapter 6. Types

Table of Contents
Introduction
Booleans
Integers
Floating point numbers
Strings
Arrays
Objects
Resource
NULL
Pseudo-types used in this documentation
Type Juggling

Introduction

PHP supports eight primitive types.

Four scalar types:

boolean
integer
float (floating-point number, aka 'double')
string

Two compound types:

And finally two special types:

This manual also introduces some pseudo-types for readability reasons:

You may also find some references to the type "double". Consider double the same as float, the two names exist only for historic reasons.

The type of a variable is usually not set by the programmer; rather, it is decided at runtime by PHP depending on the context in which that variable is used.

Note: If you want to check out the type and value of a certain expression, use var_dump().
Note: If you simply want a human-readable representation of the type for debugging, use gettype(). To check for a certain type, do not use gettype(), but use the is_type functions. Some examples:
<?php
$bool = TRUE;   // a boolean
$str  = "foo";  // a string
$int  = 12;     // an integer

echo gettype($bool); // prints out "boolean"
echo gettype($str);  // prints out "string"

// If this is an integer, increment it by four
if (is_int($int)) {
    $int += 4;
}

// If $bool is a string, print it out
// (does not print out anything)
if (is_string($bool)) {
    echo "String: $bool";
}
?>

If you would like to force a variable to be converted to a certain type, you may either cast the variable or use the settype() function on it.

Note that a variable may be evaluated with different values in certain situations, depending on what type it is at the time. For more information, see the section on Type Juggling. Also, you may be interested in viewing the type comparison tables, as they show examples of various type related comparisons.

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