R.I.B.H.U. Academy^®

Type Checking − Variable handling Functions

    Though var_dump() function tells you everything about a literal, or a variable/constant name, it cannot be used or applied in functionalities of your CMS (Content Management System) or your WEBSITE. There are many pre-defined PHP functions which are used to check the data-type of a literal, a variable or a constant. Let't examine them one by one.

gettype()

<?php echo gettype( false ); // outputs boolean ?><br />

<?php echo gettype( PHP_INT_MAX ); // outputs integer ?><br />

<?php echo gettype( 12.56 ); // outputs double ?><br />

<?php echo gettype( "true" ); // outputs string ?><br />

<?php echo gettype( [ null ] ); // outputs array ?><br />

<?php echo gettype( NULL ); // outputs NULL ?><br />

    You can see in above examples that, gettype() function outputs data-type of a literal or a variable/constant name. The output is of string data-type, that is, you can compare a literal or a variable/constant name with these 'string name' of data-types. Following codes describes you the return value from each literal. Floating point data-type is returned as double.

<?php var_dump( gettype( false ) ); // outputs string(7) "boolean" ?><br />

<?php var_dump( gettype( PHP_INT_MAX ) ); // outputs string(7) "integer" ?><br />

<?php var_dump( gettype( 12.56 ) ); // outputs string(6) "double" ?><br />

<?php var_dump( gettype( "true" ) ); // outputs string(6) "string" ?><br />

<?php var_dump( gettype( [ null ] ) ); // outputs string(5) "array" ?><br />

<?php var_dump( gettype( NULL ) ); // outputs string(4) "NULL" ?><br />

    There are other PHP pre-defined functions which can directly check the data-type of a literal or a variable/constant name. These pre-defined functions returns a boolean value, that is, when a literal or a variable/constant name is exactly same as that data-type (for which following pre-defined functions are named), the output is true. When the literal or a variable/constant name doesn't match the requied data-type, the output is false.

isset()

    You have already seen the isset() function in previous page, which outputs true when the variable/constant name has been declared and assigned a literal value. When the variable/constant name has not been defined, that is, has not been assigned with any data-type, (or has been assigned to NULL), the output is false.

<?php var_dump( isset( $not_var ) ); // variable $not_var has not been defined, and output is bool(false) ?><br />

<?php $my_var; // No value has been assigned to variable $my_var
  var_dump( isset( $my_var ) ); // outputs bool(false) ?><br />

<?php $new_var = null; // NULL represents no value.
  var_dump( isset( $new_var ) ); // outputs bool(false) ?><br />

<?php $array_var = array(); // empty array literal has been assigned to variable $array_var
  var_dump( isset( $array_var ) ); // outputs bool(true) ?><br />

<?php $string_var = ""; // empty string literal has been assigned to variable $string_var
  var_dump( isset( $string_var ) ); // outputs bool(true) ?><br />

<?php $bool_var = false; // false or true can be assigned to variable $bool_var
  var_dump( isset( $bool_var ) ); // outputs bool(true) ?><br />

    The isset() function only checks the variable/constant name, and not expressions, and literals, for example, "" (empty string), [] (empty array), NULL, etc. In following example, each code outputs the same ERROR as shown below.

<?php var_dump( isset( "" ) ); // outputs ERROR ?><br />

<?php var_dump( isset( [] ) ); // outputs ERROR ?><br />

<?php var_dump( isset( NULL ) ); // outputs ERROR ?><br />

<?php var_dump( isset( false ) ); // outputs ERROR ?><br />

is_bool()

    is_bool() function checks the literal, a variable/constant name or any expression which has been either assigned true or false or output from that expression is one of these boolean values, then output will be bool(true). You should note that is_bool() function is different from type-casting, and any integer, float, string, array evaluated as true or false are not BOOLEAN values, and therefore, output will bool(false). See the examples below:

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

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

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

<?php var_dump( is_bool( 1 ) ); // outputs bool(false) ?><br />

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

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

is_int(), is_integer(), or is_long()

    is_integer() and is_long() functions are alias of is_int() function. All these three function check whether a literal or a variable/constant name or output of an expression is an integer data-type. As explained above, all other data-types (including numeric string, empty string, floats, etc.), which can be evaluated as 0 (zero) or 1 or other integer value, will output false, when checking with these three functions.

<?php var_dump( is_int( "12" ) ); // outputs bool(false) ?><br />

<?php var_dump( is_int( intdiv( PHP_INT_MAX, PHP_INT_MIN ) ) ); // outputs bool(true) ?><br />

    intdiv() is a Math function, similar to fdiv(), but it outputs an integer value when operation is successful. Following code will output ERROR as shown below.

<?php var_dump( is_int( intdiv( PHP_INT_MIN, -1 ) ) ); // outputs ERROR ?><br />

<?php var_dump( is_int( intdiv( 1, 0 ) ) ); // outputs ERROR ?><br />

is_float(), is_double(), or is_real()

    is_double() and is_real() functions are alias of is_float() function. All these three functions check whether a literal or a variable/constant name or output of an expression is an floating point data-type. fdiv() and fmod() are Math functions, which output floating point numbers.

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

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

<?php var_dump( is_float( fdiv( 1, 0 ) ) ); // outputs bool(true) ?><br />

<?php var_dump( is_float( fmod( 21, 0 ) ) ); // outputs bool(true) ?><br />

    More Variable Handling Functions, and Checking Values of Variables, are described in next page.