How to read a function definition (prototype)
Each function in the manual is documented for quick reference. Knowing how
to read and understand the text will make learning PHP
much easier. Rather than relying on examples or cut/paste, you will want
to know how to read function definitions (prototypes). Let's begin:
Prerequisite: Basic understanding of types
Although PHP is a loosely typed language, it's important to have
a basic understanding of types as
they have important meaning.
Function definitions tell us what
type of value is returned.
Let's use the definition for strlen() as our first example:
(PHP 3, PHP 4, PHP 5)
strlen -- Get string length
int strlen ( string str )
Returns the length of string.
Explanation of a function definition
The function name.
(PHP 3, PHP 4, PHP 5)
strlen() has been around in all versions of PHP 3, PHP 4 and PHP 5
Type of value this function returns, which is an
integer (i.e. the length of a string is measured in
( string str )
The first (and in this case the only) parameter/argument for this
function is named str
, and it's a
We could rewrite the above function definition in a generic way:
returned type function name ( parameter type parameter name )
Many functions take on multiple parameters, such as in_array().
Its prototype is as follows:
bool in_array ( mixed needle, array haystack [, bool strict])
What does this mean? in_array() returns a
boolean value, TRUE on
success (if the needle
was found in the
) or FALSE on failure (if the
was not found in the
). The first parameter is named
and it can be of many different
types, so we call it
"mixed". This mixed needle
(what we're looking for) can be either a scalar value (string, integer,
or float), or an
(the array we're searching in) is the
second parameter. The third optional parameter is
. All optional parameters are seen
in [ brackets ]. The manual
states that the strict
parameter defaults to
boolean FALSE. See the manual page on each function for details on
how they work.
There are also functions with more complex PHP version information. Take
html_entity_decode() as an example:
This means that this function was not available in PHP 3, and is only
available in a released version since PHP 4.3.0.