Function Call Operations

<< Function Declaration, Arguments, and Return Values

<< PHP Tutorials - Herong's Tutorial Examples

This section describes the function call operation, which triggers the execution of the called function with arguments provided on the call.

Calling a function in PHP is simple. All you have to do is to just use the function name with an argument list in any expression:

   ... function_name(argument_1, argument_2, ...) ...

When the execution reaches this function call operation, it will:

• Evaluate all calling arguments to values or variable references.
• Assign argument values and references to argument variables defined in the "function" statement.
• Start to execute the first statement of the function body.
• Continue to execute the function body until the end of the function body or a "return" statement.
• If a "return" statement is reached with a value specified, that value is returned as this function call operation.
• If a "return" statement is reached with a no value specified, NULL is returned as this function call operation.
• If no "return" statement is reached, NULL is returned as this function call operation.

Here is a simple example script showing us how to use function call operations:

<?php # FunctionCallOperations.php
# Copyright (c) 2003 by Dr. Herong Yang. http://www.herongyang.com/
#

#  Defining a function that returns a value
   function f2c($fahrenheit) {
      $celsius = ($fahrenheit - 32.0 ) / 1.8;
      return $celsius;
   }

#  Defining a function that returns NULL
   function showAnyFooter($author) {
      print("    Copyright: $author\n");
      print("    Last Modified: 2003\n");
   }

   print("\n Function call as a standalone expression:\n");
   showAnyFooter("Herong Yang");

   print("\n Function call as an operand of another operation:\n");
   if (f2c(20.0)<0.0) print("    It's cold here!\n");

   print("\n Function call as an argument of another call:\n");
   print("    How is the temperature? ");
   print(f2c(110.0));
?>

If you run this sample script, you should get:

 Function call as a standalone expression:
    Copyright: Herong Yang
    Last Modified: 2003

 Function call as an operand of another operation:
    It's cold here!

 Function call as an argument of another call:
    How is the temperature? 43.3333333333

Last update: 2005.

Sections in This Chapter

What Is a Function?

"function" Statements - Defining Functions

Function Call Operations

Passing Arguments to Functions

Example of Passing Arguments by Values

Using Pass-by-Value Arguments for References

Example of Passing Arguments by References

Variable-Length Argument Lists

Providing Default Values to Argument Variables

Returning Values from Functions

Returning References from Functions