Introduction

Introduction

PHP supports eight primitive types.

Four scalar types:

boolean
integer
float (floating-point number, aka double)
string
Two compound types:

array
object
And finally two special types:

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

mixed
number
callback
And the pseudo-variable $....

Some references to the type "double" may remain in the manual. Consider double the same as float; the two names exist only for historic reasons.

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

Note: To check the type and value of an expression, use the var_dump() function.
To get a human-readable representation of a type for debugging, use the gettype() function. To check for a certain type, do not use gettype(), but rather the is_type functions. Some examples:
<?php
$a_bool = TRUE;   // a boolean
$a_str  = "foo";  // a string
$a_str2 = 'foo';  // a string
$an_int = 12;     // an integer

echo gettype($a_bool); // prints out:  boolean
echo gettype($a_str);  // prints out:  string

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

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