Type Juggling (original) (raw)

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

An example of PHP's automatic type conversion is the multiplication operator '*'. If either operand is a float, then both operands are evaluated asfloats, 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 and what the type of the expression itself is.

<?php <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>f</mi><mi>o</mi><mi>o</mi><mo>=</mo><mi mathvariant="normal">"</mi><mn>1</mn><mi mathvariant="normal">"</mi><mo separator="true">;</mo><mi mathvariant="normal">/</mi><mi mathvariant="normal">/</mi></mrow><annotation encoding="application/x-tex">foo = "1"; // </annotation></semantics></math>foo="1";//foo is string (ASCII 49) <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>f</mi><mi>o</mi><mi>o</mi><mo>∗</mo><mo>=</mo><mn>2</mn><mo separator="true">;</mo><mi mathvariant="normal">/</mi><mi mathvariant="normal">/</mi></mrow><annotation encoding="application/x-tex">foo *= 2; // </annotation></semantics></math>foo∗=2;//foo is now an integer (2) <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>f</mi><mi>o</mi><mi>o</mi><mo>=</mo></mrow><annotation encoding="application/x-tex">foo = </annotation></semantics></math>foo=foo * 1.3; // $foo is now a float (2.6) <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>f</mi><mi>o</mi><mi>o</mi><mo>=</mo><mn>5</mn><mo>∗</mo><mi mathvariant="normal">"</mi><mn>10</mn><mi>L</mi><mi>i</mi><mi>t</mi><mi>t</mi><mi>l</mi><mi>e</mi><mi>P</mi><mi>i</mi><mi>g</mi><mi>g</mi><mi>i</mi><mi>e</mi><mi>s</mi><mi mathvariant="normal">"</mi><mo separator="true">;</mo><mi mathvariant="normal">/</mi><mi mathvariant="normal">/</mi></mrow><annotation encoding="application/x-tex">foo = 5 * "10 Little Piggies"; // </annotation></semantics></math>foo=5∗"10LittlePiggies";//foo is integer (50) <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>f</mi><mi>o</mi><mi>o</mi><mo>=</mo><mn>5</mn><mo>∗</mo><mi mathvariant="normal">"</mi><mn>10</mn><mi>S</mi><mi>m</mi><mi>a</mi><mi>l</mi><mi>l</mi><mi>P</mi><mi>i</mi><mi>g</mi><mi>s</mi><mi mathvariant="normal">"</mi><mo separator="true">;</mo><mi mathvariant="normal">/</mi><mi mathvariant="normal">/</mi></mrow><annotation encoding="application/x-tex">foo = 5 * "10 Small Pigs"; // </annotation></semantics></math>foo=5∗"10SmallPigs";//foo is integer (50) ?>

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

To force a variable to be evaluated as a certain type, see the section onType casting. To change the type of a variable, see the settype() function.

To test any of the examples in this section, use thevar_dump() function.

Note:

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

Also, because PHP supports indexing into strings via offsets using the same syntax as array indexing, the following example holds true for all PHP versions:

<?php <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><msup><mo>=</mo><mo mathvariant="normal" lspace="0em" rspace="0em">′</mo></msup><mi>c</mi><mi>a</mi><msup><mi>r</mi><mo mathvariant="normal" lspace="0em" rspace="0em">′</mo></msup><mo separator="true">;</mo><mi mathvariant="normal">/</mi><mi mathvariant="normal">/</mi></mrow><annotation encoding="application/x-tex">a = 'car'; // </annotation></semantics></math>a=′car′;//a is a string <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mo stretchy="false">[</mo><mn>0</mn><mo stretchy="false">]</mo><msup><mo>=</mo><mo mathvariant="normal" lspace="0em" rspace="0em">′</mo></msup><msup><mi>b</mi><mo mathvariant="normal" lspace="0em" rspace="0em">′</mo></msup><mo separator="true">;</mo><mi mathvariant="normal">/</mi><mi mathvariant="normal">/</mi></mrow><annotation encoding="application/x-tex">a[0] = 'b'; // </annotation></semantics></math>a[0]=′b′;//a is still a string echo $a; // bar ?>

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 <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>f</mi><mi>o</mi><mi>o</mi><mo>=</mo><mn>10</mn><mo separator="true">;</mo><mi mathvariant="normal">/</mi><mi mathvariant="normal">/</mi></mrow><annotation encoding="application/x-tex">foo = 10; // </annotation></semantics></math>foo=10;//foo is an integer <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>b</mi><mi>a</mi><mi>r</mi><mo>=</mo><mo stretchy="false">(</mo><mi>b</mi><mi>o</mi><mi>o</mi><mi>l</mi><mi>e</mi><mi>a</mi><mi>n</mi><mo stretchy="false">)</mo></mrow><annotation encoding="application/x-tex">bar = (boolean) </annotation></semantics></math>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
(unset) - cast to NULL

(binary) casting and b prefix forward support was added in PHP 5.2.1. Note that the (binary) cast is essential the same as (string), but it should not be relied upon.

The (unset) cast has been deprecated as of PHP 7.2.0. Note that the (unset) cast is the same as assigning the value NULL to the variable or call. The (unset) cast will be removed as of PHP 8.0.0.

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

<?php <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>f</mi><mi>o</mi><mi>o</mi><mo>=</mo><mo stretchy="false">(</mo><mi>i</mi><mi>n</mi><mi>t</mi><mo stretchy="false">)</mo></mrow><annotation encoding="application/x-tex">foo = (int) </annotation></semantics></math>foo=(int)bar; <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>f</mi><mi>o</mi><mi>o</mi><mo>=</mo><mo stretchy="false">(</mo><mi>i</mi><mi>n</mi><mi>t</mi><mo stretchy="false">)</mo></mrow><annotation encoding="application/x-tex">foo = ( int ) </annotation></semantics></math>foo=(int)bar; ?>

Casting literal strings and variables to binarystrings:

<?php <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>b</mi><mi>i</mi><mi>n</mi><mi>a</mi><mi>r</mi><mi>y</mi><mo>=</mo><mo stretchy="false">(</mo><mi>b</mi><mi>i</mi><mi>n</mi><mi>a</mi><mi>r</mi><mi>y</mi><mo stretchy="false">)</mo></mrow><annotation encoding="application/x-tex">binary = (binary) </annotation></semantics></math>binary=(binary)string; $binary = b"binary string"; ?>

Note:

Instead of casting a variable to a string, it is also possible to enclose the variable in double quotes.

`<?php
foo=10;//foo = 10; // foo=10;//foo is an integer
str="str = "str="foo"; // $str is a string
fst=(string)fst = (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 information, see these sections: