Unlike many of its counterparts, PHP is not a strictly typed
language. Essentially, this means that a developer doesn’t need to explicitly
set the type (number, string, Boolean) of a variable before using it. Instead,
the PHP interpreter automatically detects variable type based on the
information stored within a variable.

While this makes programming in PHP very easy, it does have
an important drawback: when you do actually need to test a variable’s type, a
loosely typed language can be somewhat confusing to deal with. Luckily, the
developers of PHP knew this and therefore included a toolkit of functions
designed specifically to test variables and find out if they belong to a
particular character class – that is, whether they contains strings, integers,
objects or Booleans.

Table A outlines the
more useful functions available in this category and provides explanations and usage
examples.

Table A

Function

Explanation

Example

empty($var)

This function is used to check if a variable is empty (no
value or a zero value)

Use this
function to check user input — for example, form variables — to ensure that
they contain valid data.

<?php// returns false$var = “hello”;echo empty($var) ? “true” : “false”; // returns true$var = 0000;echo empty($var) ? “true” : “false”;?>
gettype($var)

This function returns the type of a variable – for
example, “string”, “integer”, “Boolean”, “float”
etc.

Use this
function to verify that variables are of the type you expect, usually before
inserting them into a strictly-typed database field.

<?php// returns string$var = “hello”;echo gettype($var); // returns double$var = 1000.56;echo gettype($var);?>
is_bool($var)

This function tests a variable to see if it contains a
Boolean (true/false) value

Use this
function to check if a variable is a Boolean variable.

<?php// returns true$var = false;echois_bool($var) ? “true” : “false”;?>
is_string($var)

This function tests a variable to see if it is a string.

Use this
function to check if a variable holds string data.

<?php// returns true$var = “exception”;echois_string($var) ? “true” : “false”; // returns true$var = “88408”;echois_string($var) ? “true” : “false”;?>
is_numeric($var)

This function tests a variable to see if it contains a
number or numeric string (strings containing a sign, numbers and decimal
points).

Use this
function to verify that a variable contains a number, usually before using it
in a calculation.

<?php// returns true$var = “+99.766”;echois_numeric($var) ? “true” : “false”; // returns false$var = “b00”;echois_numeric($var) ? “true” : “false”;?>
is_array($var)

This function tests a variable to see if it is a PHP
associative or numerically-indexed array.

Use this
function to check if a variable is an array, usually prior to processing it
in a loop.

<?php// returns true$var = array(“tiger”, “lion”, “zebra”);echois_array($var) ? “true” : “false”; // returns false$var = “zebra”;echois_array($var) ? “true” : “false”;?>
is_null($var)

This function tests a variable to see if it is NULL.

Use this
function to verify if a variable is NULL or not, usually when evaluating data
returned by an SQL query.

<?php// returns false$var = “aa”;echois_null($var) ? “true” : “false”; // returns true$var = null;echois_null($var) ? “true” : “false”;?>
is_object($var)

This function tests a variable to see if it is a PHP
object.

Use this
function to test if a variable is a PHP object, usually before calling a
method or accessing a property.

<?php// returns false$var = “exception”;echois_object($var) ? “true” : “false”; // returns true$var = new Exception;echois_object($var) ? “true” : “false”;?>
isset($var)

This function tests a variable to see if it has already
been defined.

Use this
function to test if a variable has been defined, usually when evaluating the
results of a form submission.

<?php// returns true$var = “yes”;echoisset($var) ? “true” : “false”; // returns falseechoisset($test) ? “true” : “false”;?>
print_r($var)

This function prints the contents of a variable.

Use this
function to “look inside” a variable, typically when debugging a
script.

<?php$var = array(“one”, “two”, array(“red”, “green”), new Exception, 467);print_r($var);?>