PHP Variables and PHP Built-in Functions with Examples

PHP Variables and built in functions

What are the PHP Variables:

Definition and syntax:

PHP Variables are intended to store data that will be used and can be modified when running the program. The PHP language, like the Perl language, uses a particular form of syntax for defining a variable. PHP Variables are represented with a “$” character prefixing the identification of this variable. For example, to declare a new name variable “myVariable”, just call it $myVariable inside the source code. identifiers prior to their use. The PHP Variables are therefore said to be untyped, that is to say, that a variable can take a character string value and then be used to contain an integer. The type is defined when this variable is assigned. It is partly this great flexibility of use which makes PHP a language simple and fast to access. In the example below, you can see how easy it is to use PHP Variables:

PHP Variables and built in functions

The name of the variable can be defined by all alphanumeric characters as well as by the character ’_’, but it cannot start with a number. $myVariable, $_myVariable, $myVariable1 are valid PHP Variables. On the other hand, $ 1maVariable will cause a syntax error.

What is PHP $ and $$ variables Or Dynamic PHP Variables:

Dynamic PHP Variables are variables whose name depends on other PHP Variables. The names of these PHP Variables are therefore constructed dynamically while executing PHP code. The example below is much more telling than a long speech:

Thus, by simply writing $$dyn we get the value of the variable whose name is contained in $dyn, that is, $var. The use of dynamic PHP Variables is generally not necessary, as they can, although often to be advantageously replaced by the use of tables, but who knows … it is possible that it will help you out one day!

It is often preferable, and sometimes essential, to put the name of the PHP Variables between braces. This will allow you, for example, to create a variable name with a part variable and a fixed part, as is the case in the following example:

The result would obviously have been quite different if we had used $dynfix. The problem is identical when it comes to selecting an element of an array; $$dyn [0] is ambiguous, unlike $ {$dyn [0]} and $ {$ dyn} [0].

Types of PHP Variables:

As we have seen, PHP variables do not have a predefined type. Yet a developer may need to manipulate types for the needs of an application and conversion problems may not cause errors, but return results surprising and embarrassing. To avoid this, the PHP language has a set of functions which allows you to set and retrieve the type of a given variable. We can classify the different possible types into three categories: scalar types, compounds and special types.

Table 1: Definitions of the four scalar types of PHP variables

Type Description Example
int (or integer)


The int type is used to contain

integers (numbers without comma).

Values ​​can range from

–2147483648 to 2147483647.

$myVariable = 2;

$myVariable = −4;

$myVariable = 2002;

double (or real or float) The double type is used to define

decimal numbers, that is to say

with a floating point.

$myVariable = 1.0;

$myVariable = −0.1

$myVariable =


String The type string defines a string

of characters.

$myVariable = “Long live it php! “;

$myVariable = “1”;

boolean (or bool) The boolean type defines a variable

taking binary type values:


$myVariable = TRUE;

$myVariable = FALSE;

$dec,  hex and $oct have the same value but expressed in a base different. Note that it is not possible to express a number directly in its form binary.

Table 2: The two compound types of PHP variables

Type Description Example
Array Designates an array type (set of


$myArray = array (2,

“Great, PHP!”,

“key” => “value”);

$ myArray [2] = “Top”;

Object Designates an object type (variable

having its own properties,

attributes and methods).


class MyClass



$myObject = new



Table 3: The two special types supported PHP Variables

Type Description
resource Represents a reference (e.g .: connection identifier to a database

or any other source).

NULL The NULL type variable represents a variable that has no value.


Although the type of PHP Variables is defined at their initialization, it is still possible to force a variable into a given type.

PHP Built-in Functions:

Built-in Function settype():

Assigns a type to a variable.

Syntax:  boolean settype ($variable, string $type)

$variable: Variable whose type we want to set.

$type: Character string specifying the type that we want to assign to the variable.

It can be either:

integer for an integer type.

double for a real type.

string for a character string.

array for an array.


TRUE on success or FALSE (eg: invalid type name).

Built-in Function getType ():

To retrieve the type you will use the gettype () function.

Returns the type of the variable.

Syntax: string getType ($variable)

$variable: Variable whose type we want to determine.

Return: The different possible return values ​​are:

integer for an integer type.

double for a real type.

string for a character string.

array for an array.

object for an object.

resource for a resource (a pointer to …).

user function for a function created by the user.

unknown type for an unknown type.

The code below is a good example of this use:

In your data manipulations, you may need to test the existence or the type of PHP Variables you use. For this, we use a very useful set of functions.

Built-in Function  isSet ():

Determines whether a variable exists (has been initialized).

Syntax: boolean isSet ($variable)

$variable: Variable that we want to test.

return: TRUE if the variable exists and FALSE otherwise.

Built-in Function unset():

Destroys the variables.

Syntax: void unset ($variable1 [,$variable2 [, …]])

$variable1, …: The variables to destroy.

Likewise, the empty () function determines whether a variable has a value not zero or not.

Built-in Function empty():

Determines whether a variable has a non-zero value or not.

Syntax: boolean empty ($variable)

$variable: Variable that we want to test.

return: TRUE if the variable does not exist, is an empty string (’’) or is 0, NULL, FALSE otherwise.

PHP Variables and built in functions

To destroy a variable, use the unset () function. In order to test the type of PHP Variables, PHP has a series of very convenient functions:

is_bool (),

is_int (),

is_double (),

is_numeric (),

is_string (),

is_array (),

is_scalar (),

is_object (),

is_resource ()

is_NULL ().

All of these functions are used in the same way. They return TRUE if the type of the variable passed as a parameter is exactly the type sought, and FALSE otherwise.

Built-in Function  is_bool ()

Determines whether a variable is of type Boolean.

Syntax: boolean is_bool ($variable)

$variable: Variable which we want to determine if it is of Boolean type.

return: TRUE if the variable is of Boolean type, FALSE otherwise.

Built-in Function is_int()

Determines whether a variable is of type integer.

Syntax: boolean is_int ($variable)

$variable: Variable which we want to determine if it is of integer type.

return: TRUE if the variable is of integer type, FALSE otherwise.

is_int () is actually an alias of is_long () of which is_integer () is another alias.

Built-in Function  is_double()

Determines whether a variable is of type real (decimal).

Syntax: boolean is_double ($variable)

$variable: Variable which we want to determine if it is of real type.

return: TRUE if the variable is of real type, FALSE otherwise.

is_float () and is_real () are aliases of the is_double () function.

Built-in Function  is_numeric()

Determines whether a variable is a number or a character string representing a number.

Syntax:boolean is_numeric ($variable)

$variable: Variable which we want to determine if it is of type number or string of characters representing a number.

return: TRUE if the variable is of type number or string representing a number, FALSE otherwise.

Built-in Function is_string()

Determines whether a variable is of type string.

Syntax: boolean is_string ($variable)

$variable: Variable which we want to determine if it is of type character string.

return: TRUE if the variable is a character string, FALSE otherwise.

Built-in Function is_array()

Determines whether a variable is of type array.

Syntax: boolean is_array ($variable)

$variable: Variable which we want to determine if it is of array type.

return: TRUE if the variable is of array type, FALSE otherwise.

Built-in Function  is_object ()

Determines whether a variable is of type object.

Syntax: boolean is_object ($variable)

$variable: Variable which we want to determine if it is of type object.

return: TRUE if the variable is of object type, FALSE otherwise.

Built-in Function is_scalar ()

Determines whether a variable is of scalar type.

Syntax: boolean is_scalar ($variable)

$variable: Variable which we want to determine if it is of scalar type.

return: TRUE if the variable is of scalar type, FALSE otherwise.

Built-in Function is_resource ()

Determines whether a variable is of type resource.

Syntax: boolean is_resource ($variable)

$variable: Variable which we want to determine if it is of type resource.

return: TRUE if the variable is of type resource, FALSE otherwise.

Built-in Function is_NULL ()

Indicates whether a variable is NULL.

Syntax: boolean is_NULL ($variable)

$variable: Variable which we want to determine if it is NULL.

return: TRUE if the variable is NULL, FALSE otherwise.

External PHP Variables:

We can differentiate two types of external PHP Variables:

  • Environment PHP Variables (from the server);
  • Variables passed as a parameter when calling the page (either via a form or via URL).

Environment PHP Variables:

Environment PHP Variables are variables automatically generated by PHP from from the data retrieved from the server or from the client request header.

These PHP Variables in fact constitute two tables of global scope (accessible from any which place in the script):

  • $ _ENV contains the “real” server environment PHP Variables, i.e. all PHP Variables that the account under which the web server is running (eg: PATH) may have inherited.
  • $ _SERVER contains, for its part, the “internal” PHP Variables of the server (name and version of the server, IP address, etc.) as well as those retrieved from the client (client IP address, type of browser, etc.).

You can simply view all the environment variables on the generated page by the phpinfo () function.

Another possibility to retrieve the list of variables is to use the function get_defined_vars (); it allows you to retrieve the list of all the PHP Variables in an array defined. The returned array then contains all the environment PHP Variables, but also all user-defined PHP Variables.

Built-in Function get_defined_vars ()

List all defined variables.

Syntax: array get_defined_vars (void)

return: All the PHP Variables in an associative array where the names of the keys are the variable names and the values ​​of the variables.

The example below generates an HTML table containing the list of PHP Variables and their values ​​when the code is executed:

The array $ _ENV is generally not of great interest except in a few cases individuals. You can also retrieve the values ​​using the getEnv () function.

Built-in Function getEnv()

Returns the value of an environment variable.

Syntax: string getEnv (string $ environmentVariable)

$variable Environment: Environment variable whose value we want to determine.

Return: The value of the environment variable or FALSE if there is an error

It is very easy to modify environment variables using the putEnv () function. The values ​​thus set by the developer only last as long as the script is running and, as soon as it ends, the default environment is restored. But, as changing some values ​​can cause problems with security, the system administrator has the ability to prevent certain changes. It is Moreover, by default, the case of the LD_LIBRARY_PATH variable (from a UNIX / Linux system) which, if it were to be changed, could possibly allow hackers to hide the presence of a library (perhaps used by the web server) for the benefit of another more malicious. Thus, the safe_mode_protected_env_vars directive of the configuration file php.ini contains a list of environment PHP Variables that the developer cannot modify. Likewise, if safe_mode (protected mode) is enabled (which is not the case by default), only PHP Variables starting with the prefixes specified in safe_mode_allowed_env_vars may be changed.

Built-in Function putEnv ()

Set a new value for the environment variable.

Syntax: void putEnv (string $assignmentString) $stringAssignment Character string of the form “<variable name> = <value>”

The $ _SERVER array, for its part, will allow us to perform many operations.

cast or type casting in php:

To remedy the problems that you may encounter in your handling of conversion, the developer has the option of using cast (or type casting). Under this somewhat barbaric term, hides the possibility of creating a new variable containing the value another with a different but compatible type. Thus, the cast allows a programmer to modify the type of this PHP Variables during the execution of his program, that either to test for equality or to perform operations between two variables of different types. The cast is used, as for the C language, by writing the type in parentheses before the name of the variable, as shown in the example below:

The different possible conversions are therefore:

  • (array) to convert to array type.
  • (boolean) or (bool) to convert to boolean type.
  • (double), (float) or (real) to convert to real type (decimal).
  • (int) or (integer) to convert to the integer type.
  • (object) to convert to type object.
  • (string) to convert to type string.

In the following example, we show how, from converting to an array or an object, a programmer can recover the data:

Note that converting a scalar type variable (int, double or string) into the type object will create an attribute named scalar and containing the value of the variable.

PHP Variables references:

PHP allows creating a reference to an existing variable. In the same way, as with the C language, you can directly access a memory area containing a variable. The reference to a variable allows you to create a new variable that uses the same zone memory as the original variable. To do this, you must indicate it using the character ’&’ in front of the variable name, such as show the following example:

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