Variable variables in PHP allow the name of a variable to be dynamically set and accessed using the value of another variable. They are useful for situations where variable names need to be dynamically generated, such as when uniquely identifying employees or students with IDs. Examples shown include outputting a name based on an ID variable, generating variables from an array, and simulating Excel's indirect() function to create dependent drop-down lists in a form. Variable variables can reduce code, provide a central sanitization point for external inputs, and make variable names easier to modify.

1. PHP Variable Variables
Examples
Abdul Rahman Sherzad
Computer Science Lecturer
Herat University, Afghanistan

2. Definition
■ Variable variables take the value
of one variable, and treat that as
the name of another variable.
■ Variable variables are just
variables whose names can be
programmatically set and
accessed. Hence, they are also
called dynamic variable names.
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3. Example 1
■ Employees share similar name. Hence, all
employees are given a unique identifier (ID, aka
code) by organizations. This unique code is
important for the organizations to distinguish their
employees.
■ Likewise, educational institutions assign a unique
code for their students.
■ This unique code is very important for the system,
but it alone is not very informative in reports.
■ Variable variables can be used in such situations to
cover both. Following code creates a variable called
$S20120, and outputs the string "Abdul Rahman
Sherzad".
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4. Example 2
■ It is also possible to use value of a
variable/literal value as part of variable
variables names.
■ Of course, there are many other easy
ways to accomplish the functionality of
this program. But this is to explain
variable variables concept through
examples.
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5. Example 2 - Array
■ This is another method to
accomplish Example 2 in the
previous slide using array.
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6. Example 3
■ Variable variables can be used to
dynamically generate variables from an
associative array.
■ The PHP extract() built-in function also
takes an associative array and treats the
keys as variable names and the values
as variable values, (see next slide).
■ This example is to describe and
demonstrate the variable variables
applications, not reinventing the wheel.
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7. Example 3 - Extract
■ The PHP extract() function takes an
associative array and treats the keys as
variable names and the values as
variable values.
■ The extract() has useful functionality
such as to prevent variables that already
exist.
■ Also it enables one to group the variables
by using prefixes too.
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8. Example 4
■ Use variable variables to convert POST
variables to local variables, as illustrated
in the example.
■ This technique has several benefits.
– Lines of code are reduced,
– Central place to clean and sanitize
all external input,
– Easy change and modification of
variable names.
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9. Example 5
■ PHP variable variables can simulate
Microsoft Excel’s indirect() function to
create dependent drop-down lists.
■ In this example, it is shown how to create
dependent drop-down lists, using
variable variables names.
■ Of course, there are better ways to
accomplish creating dependent drop-
down lists. In this presentation, the
purpose is to show the application and
example of variable variables in PHP.
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10. Example 5 - complete
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