Assign the default value to the parameters inside the function
prototype:
function wrap_html_tag($string, $tag = 'b') {
return "<$tag>$string</$tag>";
}
The example in the Solution sets the default tag value to
b, for bold. For example:
$string = 'I am some HTML';
wrap_html_tag($string);
returns:
<b>I am some HTML</b>
This example:
wrap_html_tag($string, 'i');
returns:
<i>I am some HTML</i>
There are two important things to remember when assigning
default values. First, all parameters with default values must appear after
parameters without defaults. Otherwise, PHP can't tell which parameters are
omitted and should take the default value and which arguments are overriding the
default. So wrap_html_tag( ) can't be defined
as:
function wrap_html_tag($tag = 'i', $string)
If you do this and pass wrap_html_tag( ) only a single
argument, PHP assigns the value to $tag and issues a warning
complaining of a missing second argument.
Second, the assigned value must be a constant, such as a string
or a number. It can't be a variable. Again,
using wrap_html_tag( ), such
as our example, you can't do this:
$my_favorite_html_tag = 'i';
function wrap_html_tag($string, $tag = $my_favorite_html_tag) {
...
}
If you want to assign a default of nothing, one solution is to
assign the empty string to your parameter:
function wrap_html_tag($string, $tag = '') {
if (empty($tag)) return $string;
return "<$tag>$string</$tag>";
}
This function returns the original string, if no value is
passed in for the $tag. Or if a (nonempty) tag is passed in, it returns
the string wrapped inside of tags.
Depending on circumstances, another option for the
$tag default value is either 0 or NULL. In
wrap_html_tag( ), you don't want to allow an empty-valued tag. However,
in some cases, the empty string can be an acceptable option. For instance, join( ) is often called on the empty string,
after calling file( ), to place a file into a
string. Also, as the following code shows, you can use a default message if no
argument is provided but an empty message if the empty string is passed:
function pc_log_db_error($message = NULL) {
if (is_null($message)) {
$message = 'Couldn't connect to DB';
}
error_log("[DB] [$message]");
}
