PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

144 Chapter 5 Reusing Code and Writing Functions
In this case, the parameter used is a string containing only the word parameter, but the
following calls may also be fine depending on what parameters the function expects:
function_name(2);
function_name(7.993);
function_name($variable);
In the last line, $variable might be any type of PHP variable, including an array or
object.
A parameter can be any type of data, but particular functions usually require particular
data types.
You can see how many parameters a function takes, what each represents, and what
data type each needs to be from the function’s prototype.We often show the prototype in
this book when we describe a function.
This is the prototype for the function fopen():
resource fopen ( string filename, string mode
[, bool use_include_path [, resource context]])
The prototype tells you a number of things, and it is important that you know how to
correctly interpret these specifications. In this case, the word resource before the function
name tells you that this function will return a resource (that is, an open file handle).
The function parameters are inside the parentheses. In the case of fopen(), four parameters
are shown in the prototype.The parameters filename and mode are strings, the
parameter use_include_path is a Boolean, and the parameter context is a resource.The
square brackets around use_include_path and context indicate that these parameters
are optional.You can provide values for optional parameters, or you can choose to ignore
them and the default value will be used. Note, however, that for a function with more
than one optional parameter, you can only leave out parameters from the right. For
example, when using fopen(), you can leave out context or you can leave out both
use_include_path and context; however, you cannot leave out use_include_path but
provide context.
After reading the prototype for this function, you know that the following code fragment
is a valid call to fopen():
$name = ‘myfile.txt’;
$openmode = ‘r’;
$fp = fopen($name, $openmode);
This code calls the function named fopen().The value returned by the function will be
stored in the variable $fp. For this example, we chose to pass to the function a variable
called $name containing a string representing the file we want to open and a variable
called $openmode containing a string representing the mode in which we want to open
the file.We chose not to provide the optional third and fourth parameters.