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Type Casting

    You have seen some type-casting in previous pages, but in this topic, it will be described elaborately. As a programmer, you should think on every possible options in which a user can input data. Since PHP is a loose data-type scripting language, you should be carefully examine every data, you may encounter.

Boolean to Other Data-types

    When true is type-casted to integer or float data-type, it is converted to 1. When false is type-casted to integer or float data-type, it is converted to 0.

<?php var_dump( (int) true ); // int(1) ?><br />

<?php var_dump( (int) false ); // int(0) ?><br />

<?php var_dump( (float) true ); // float(1) ?><br />

<?php var_dump( (float) false ); // float(0) ?><br />

    When true and false are type-casted to (string) data-type, they are converted to "1" and "" (empty string) respectively.

<?php var_dump( (string) true ); // string(1) "1" ?><br />

<?php var_dump( (string) false ); // string(0) "" ?><br />

    When true and false are type-casted to (array) data-type, they are added as first item (element) to an empty array. The values of those items are respectively same as those boolean values.

<?php var_dump( (array) true ); // array(1) { [0] => bool(true) } ?><br />

<?php var_dump( (array) false ); // array(1) { [0] => bool(false) } ?><br />

Integer to Other Data-types

    An integer can be negative, zero, or positive number. Outputs from following codes are shown in comment, which is self-explanatory. When 0 is type-casted to (boolean) data-type, the output is false. All other values are treated as true.

<?php var_dump( (bool) -5 ); // bool(true) ?><br />

<?php var_dump( (bool) 0 ); // bool(false) ?><br />

<?php var_dump( (bool) -5 ); // bool(true) ?><br />

    When any integer is type-casted to float or string data-type, its value is same, as shown below in comments. When 0 is type-casted to (string), it is converted into an empty string.

<?php var_dump( (float) -3 ); // float(-3) ?><br />

<?php var_dump( (float) 0 ); // float(0) ?><br />

<?php var_dump( (float) 3 ); // float(3) ?><br />

<?php var_dump( (string) -4 ); // string(2) "-4" ?><br />

<?php var_dump( (string) 0 ); // string(0) "" ?><br />

<?php var_dump( (string) +4 ); // string(1) "4" ?><br />

    When any integer value is type-casted to (array) data-type, it is added as first item of an empty array. Output is shown in comments.

<?php var_dump( (array) -6 ); // array(1) { [0] => int(-6) } ?><br />

<?php var_dump( (array) 0 ); // array(1) { [0] => int(0) } ?><br />

<?php var_dump( (array) +6 ); // array(1) { [0] => int(6) } ?><br />

Floating Point Numbers to Other Data-types

    Other than negative, zero, and positive floating point numbers, there are reserved keywords, INF, -INF, NAN,M_PI, etc. which are also float data-type. Type-casting of these (pre-defined) constants are as follows:

<?php var_dump( (bool) INF ); // bool(true) ?><br />

<?php var_dump( (bool) -INF ); // bool(true) ?><br />

<?php var_dump( (bool) NAN ); // bool(true) ?><br />

<?php var_dump( (bool) M_PI ); // bool(true) ?><br />

    In above codes, you can see that NAN (Not A Number) is not equal to bool(false). However, when these pre-defined constants, that is, INF, -INF and NAN are type-casted to (int) or (integer), their values are all 0. Constant M_PI is the value of pi() function, and when type-casted to (integer), it is truncated to 3.

<?php var_dump( (integer) INF ); // int(0) ?><br />

<?php var_dump( (integer) -INF ); // int(0) ?><br />

<?php var_dump( (integer) NAN ); // int(0) ?><br />

<?php var_dump( (integer) M_PI ); // int(3) ?><br />

<?php var_dump( (string) INF ); // string(3) "INF" ?><br />

<?php var_dump( (string) -INF ); // string(4) "-INF" ?><br />

<?php var_dump( (string) NAN ); // string(3) "NAN" ?><br />

<?php var_dump( (string) M_PI ); // string(15) "3.1415926535898" ?><br />

<?php var_dump( (array) INF ); // array(1) { [0] => float(INF) } ?><br />

<?php var_dump( (array) -INF ); // array(1) { [0] => float(-INF) } ?><br />

<?php var_dump( (array) NAN ); // array(1) { [0] => float(NAN) } ?><br />

<?php var_dump( (array) M_PI ); // array(1) { [0] => float(3.141592653589793) } ?><br />

    You can see in above codes that when these pre-defined constants are type-casted to (array) data-type, these floating point numbers are added as first item to an empty array.

    All floating point numbers (except pre-defined constants), that is, negative, zero and positive floating point numbers behave just like integers, except, when they are type-casted to (integer), the fractional part (digits after the decimal point/dot) is truncated. See previous page for reference.

Strings to Other Data-types

    Strings can be classified as different values, for example, "" (empty string, without any blank space within it), "+12.4" (numeric string, either signed or unsigned, without underscore symbols), and "false" (non-numeric string, whether characters within a pair of single/double quotes are pre-defined constants).

<?php var_dump( (bool) "" ); // bool(false) ?><br />

<?php var_dump( (bool) "-1.2" ); // bool(true) ?><br />

<?php var_dump( (bool) "false" ); // bool(true) ?><br />

<?php var_dump( (int) "" ); // int(0) ?><br />

<?php var_dump( (int) "-12.5" ); // int(-12) ?><br />

<?php var_dump( (int) "INF" ); // int(0) ?><br />

<?php var_dump( (float) "" ); // float(0) ?><br />

<?php var_dump( (float) "-12.5" ); // float(-12.5) ?><br />

<?php var_dump( (float) "INF" ); // float(0) ?><br />

<?php var_dump( (array) "" ); // Array (1) { [0] => string(0) "" } ?><br />

<?php var_dump( (array) "-12.5" ); // Array (1) { [0] => string(5) "-12.5" } ?><br />

<?php var_dump( (array) "INF" ); // Array (1) { [0] => string(3) "INF" } ?><br />

    You can visit previous page to see more type-casting from string data-type to other data-type, and vice-versa.

Arrays to Other Data-types

    Arrays can be classified into either empty array or non-empty array for purpose of type-casting to other data-types. Arrays cannot be type-casted to (string) data-type. Conversion of an array to a string can be done with implode() function. Similarly, a string (with some separator) can be converted into an array, with explode() function.

<?php var_dump( (bool) [] ); // bool(false) ?><br />

<?php var_dump( (int) [] ); // int(0) ?><br />

<?php var_dump( (float) [] ); // float(0) ?><br />

<?php var_dump( (string) [] ); // shows ERROR as shown below ?><br />

<?php var_dump( (bool) [ false ] ); // bool(true) ?><br />

<?php var_dump( (int) [ 0 ] ); // int(1) ?><br />

<?php var_dump( (float) [ 1.2 ] ); // float(1) ?><br />

<?php var_dump( (string) [ "" ] ); // shows ERROR as shown below ?><br />

<?php var_dump( (bool) [ false, true, null ] ); // no matter how many items are inside an array, output is bool(true) ?><br />

<?php var_dump( (int) [ 23, 34, true, 6534 ] ); //no matter how many items are inside an array, output is int(1) ?><br />

<?php var_dump( (float) [ 1.2, false, 234, 34.32 ] ); // no matter how many items are inside an array, output is float(1) ?><br />

NULL to Other Data-types

    null can be type-casted to other data-types. However, conversion of other data-types to null is DEPRECATED as of PHP 7.2.0, and REMOVED as of PHP 8.0.0. Relying on this feature is highly discouraged. Casting a variable to null using (unset) is also DEPRECATED as of PHP 7.2.0, and REMOVED as of PHP 8.0.0.

<?php var_dump( (bool) null ); // bool(false) ?><br />

<?php var_dump( (int) null ); // int(0) ?><br />

<?php var_dump( (float) null ); // float(0) ?><br />

<?php var_dump( (string) null ); // string(0) "" ?><!-- Output is empty string --><br />

<?php var_dump( (array) null ); // array(0) { } ?><!-- Output is empty array --><br />