Page 182 - Beginning PHP 5.3

Part II: Learning the Language

Figure 7-1

Working with Variable Functions

When you include a function call in your code, most of the time you ’ ll know the name of the function
you want to call. However, sometimes it ’ s useful to be able to store the name of a function in a string
variable, and use that variable instead of the function name when calling a function. Here ’ s an example:

$squareRoot = “sqrt”;
echo “The square root of 9 is: “ . $squareRoot( 9 ) . “. < br/ > ”;

echo “All done! < br/ > ”;
As you can see, the first line of code stores the function name, “ sqrt ” , as a string in the $squareRoot

variable. This variable is then used in place of the function name on the second line.
This example is fairly trivial, but it shows how the concept works. Here ’ s a slightly more complex
example:

$trigFunctions = array( “sin”, “cos”, “tan” );
$degrees = 30;

foreach ( $trigFunctions as $trigFunction ) {
echo “$trigFunction($degrees) = “ . $trigFunction( deg2rad( $degrees ) )
. “ < br/ > ”;

}

This code creates an array of three built - in function names — “ sin ” “ cos , and “ tan “ — and sets up a
,

”
$degrees variable. It then loops through the array. For each element, it calls the function whose name is
stored in the element, passing in the value of $degrees converted to radians (using PHP ’ s built - in
deg2rad() function), and displays the result. Here ’ s the output from the code:

144

9/21/09 9:00:52 AM
c07.indd 144
c07.indd 144 9/21/09 9:00:52 AM