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# How to read a function definition (prototype)

Each function is documented for quick reference, knowing how to read and understand the manual will make using PHP much easier. Rather than relying on examples or cut/paste, you want to know how to read function definitions (prototypes). Let's begin:

> Prerequisite: Basic understanding of types: Although PHP is a loosly 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:

    strlen

    (PHP 3, PHP 4 >= 4.0.0)
    strlen -- Get string length

    Description
    int strlen ( string str )

    Returns the length of string.

Table K-1. Explanation of a function definition

Part | Description
--- | ---
strlen | The function name.
(PHP 3, PHP 4 >= 4.0.0) | strlen() has been around in both all of PHP 3 and PHP 4
int | Type of value this function returns, which is an integer (i.e. The length of a string is measured in numbers).
( string str ) | The first (and in this case the only) parameter/argument for the function strlen() is named `str`, and it's a string.

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(). It's 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 (the `needle` was found in the `haystack`) or `FALSE` on failure (the `needle` was not found in the `haystack`). The first parameter is named `needle` and it can be many different types, so we call it "mixed". This mixed `needle` (what we're looking for) can either be a scalar value (string, integer, or float), or an array. `haystack` (the array we're searching in) is the second parameter. The third optional parameter is named `strict`. 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.

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