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   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:

     * array
     * object

   And finally two special types:

     * resource
     * NULL

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

     * mixed
     * number
     * callback

   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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