Creating a function to act on many variables - php

Question

php noob here trying to create a function but can't quite find the resource on the web that rids my confusions. Here it goes;
I want to create a function which takes a variable name, for example
Thief's Wit (4)
And converts it to
thiefswit.jpg
So far, here is what I have
THIS CODE IS LOADED TO TEST MY FUNCTION
require_once 'functions.php';
$mod = "Thief's Wit (4)";
convertImage($mod);
echo $mod;
?>
THIS CODE IS THE ACTUAL FUNCTION
function convertImage($string)
{
$string = preg_replace('/\s+/', '', $string);
$string = str_replace("'", "", $string);
$stringlength = strlen($string);
substr ($string, 0, ($stringlength-4));
$string = strtolower ($string);
$string = "$string" . ".jpg";
return $string;
}
?>
The format of the strings will always be
NAME HERE (4)
which is why I substr the length-4.
When I run this function, it echoes the original string.
Any help here?
I'm new to PHP and don't really understand
a) What the 'return' does at the end of the function and
b) Does the function inherently know to replace "$string" with the variable you tell it to act on in another file? In this case $mod.
Thanks!

Answer 1

You need to save the output of the function:
$mod = "Thief's Wit (4)";
$mod = convertImage($mod); // save the return value to $mod variable
echo $mod;
The return value of a function is the value you get from calling a function. So convertImage($mod) will have the value that you return. At this point, you need to store the results to a variable, which you can do by doing $mod = convertImage($mod);
An alternative would be to "pass by reference", where modifying the arguments of your function will modify the variables themselves.
function convertImage(&$string) // use &$string to pass by reference
{
$string = preg_replace('/\s+/', '', $string);
$string = str_replace("'", "", $string);
$stringlength = strlen($string);
substr ($string, 0, ($stringlength-4));
$string = strtolower ($string);
$string = "$string" . ".jpg";
//return $string; this won't be needed anymore
}
...
$mod = "Thief's Wit (4)";
convertImage($mod);
echo $mod;

Answer 2

You have to either return the new string you created
$mod = convertImage($mod);
Or pass by reference, which means that the function convertImage is working with the same reference to the passed in string as its caller
function convertImage(&$string) {...}
convertImage($mod); // $mod will point to a new string after the call

Answer 3

function convertImage(&$string) {
$string = strtolower(preg_replace("/[^a-zA-Z]+/", "", $string));
}
should do all you need - it will strip any punctuation and numbers etc, and make it lower case.
edited to allow passing by reference

Answer 4

You aren't assigning the variable value anywhere. To get the actual result, you'd have the function return value to a variable, like so:
$mod = convertImage($mod);
Once the actual function output is stored in a variable, you'll be able to use it anywhere as you like.
Demo: http://codepad.org/naFB74K6

Answer 5

<?php
function convertImage(&$string)
{
$string = preg_replace('/\s+/', '', $string); //Thief'sWit(4)
$string = str_replace("'", "", $string); //ThiefsWit(4)
$string = substr($string, 0, strlen($string)-3); //ThiefsWit
$string = strtolower($string); //thiefswit
return $string.".jpg";
}
$mod = "Thief's Wit (4)";
convertImage($mod);
echo $mod;
?>