Functions
A function is a named sequence of code
statements that can optionally accept parameters and return a value.
A function call is an expression that has a value; its value is the
returned value from the function. PHP provides a large number of
internal functions. The Section 16.13 lists all of the commonly
available functions. PHP also supports user-definable functions. To
define a function, use the function
keyword. For
example:
function soundcheck($a, $b, $c) { return "Testing, $a, $b, $c"; }
When you define a function, be careful what name you give it. In particular, you need to make sure that the name does not conflict with any of the internal PHP functions. If you do use a function name that conflicts with an internal function, you get the following error:
Fatal error: Can't redeclare already declared function infilename
on lineN
After you define a function, you call it by passing in the appropriate arguments. For example:
echo soundcheck(4, 5, 6);
You can also create functions with optional parameters. To do so, you
set a default value for each optional parameter in the definition,
using C++ style. For example, here’s how to make all
the parameters to the soundcheck()
function
optional:
function soundcheck($a=1, $b=2, $c=3) { return "Testing, $a, $b, $c"; }
Passing Arguments to Functions
There are two ways you can pass arguments to a function: by value and by reference. To pass an argument by value, you pass in any valid expression. That expression is evaluated and the ...
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