All About User Defined Functions in PHP

So far we’ve been using PHPs built-in functions to do our tasks; we also
declared and used user-defined function in the post Creating
a Simple Visitor Counter in PHP. However, we didn’t discuss much
about them. For those of you who are curious to know more about user-defined
functions or those who’d doubts, I’ve written this post. Read along
to know more about user-defined functions.

Declaring functions

In PHP functions are declared using the keyword ‘function’ as below:

function func-name(arg-list)


{

    …

}

Here ‘arg-list’ may be empty if you don’t want the function
to take any arguments.

If you remember from the post Creating
a Simple Visitor Counter in PHP, we’d stated that no matter whether
the function returns a value or not, no return type has to be specified for
the function (unlike C/C++).

a. Functions having parameters

function myfunc($a)


{

    echo $a;


}

b. Functions returning values

function myfunc($a)


{

    return 2*$a;


}

Scope of variables inside and outside of function

1. 
   

   Variables declared inside a function are called local variables and re
   only accessible within the function.

   
   


2. 
   

   Variables declared outside functions are called global variables STILL
   they are NOT directly accessible from inside functions.

   
   

Have a look at the following code:



function myfunc()


{

    $a=10;


}

echo $a;


//$a will not be accessible




//for global varaible

$a=10


function myfunc2()


{

    //again $a not accessible


    echo $a;


}

There is nothing we can do to make local variables accessible outside the
function however global variables can be made accessible inside functions by
explicitly defining that particular function as ‘global’ inside
the function.

$a=10


function myfunc2()


{

    global $a;


    //now $a=10 is accessible


    echo $a;


}

Naming functions

1. 
   

   Two functions cannot have the same name neither your functions can have
   the same name as an existing function. PHP DOES NOT SUPPORT FUNCTION OVERLOADING.

   
   


2. 
   

   Function name may have letters, digits and underscores.

   
   


3. 
   

   Function name cannot begin with a digit.

   
   


4. 
   

   Functions can be of the same name as a variable though.

   
   

Previous Articles:

• 
  

  Sorting
  Arrays in PHP…Some Sorting Functions

  
  


• 
  

  Creating
  a Simple Visitor Counter in PHP

  
  


• 
  

  
  String Manipulation Functions in PHP II

  
  


• 
  

  Creating
  a ‘Contact Us’ Form (E-Mail Version)

  
  


• 
  

  Creating
  a Simple ‘Contact Us’ Form in PHP

  
  

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