Creating functions: what's the point?

Davidc316

I'm confused.

Any beginners PHP book will tell you how to create and call functions.

But read on a few pages and you'll soon (no doubt!) be told about how to use include() to call upon any php script you have at will.

QUESTION: What's the point of creating your own functions when you can just use include statements instead?

For example. Let's imagine you have a function that does a mathematical calculation. Why not just write a php script that does the calculation then use include() whenever you want to call that function?

devinemke

Originally posted by Davidc316
For example. Let's imagine you have a function that does a mathematical calculation. Why not just write a php script that does the calculation then use include() whenever you want to call that function?

another example: Let's imagine you have 100 different functions that do 100 different mathematical calculations. by your logic you would have to include 100 different files. if you put all 100 in a single file as functions you would need to only include 1 file. make sense?

tekky

Originally posted by Davidc316
.....QUESTION: What's the point of creating your own functions when you can just use include statements instead?

For example. Let's imagine you have a function that does a mathematical calculation. Why not just write a php script that does the calculation then use include() whenever you want to call that
function?

well, why bother using includes if you are going to make it a function anyways?

several reasons to use a function.....

I have this code that checks data against a database... and I do it 1000 times each time I do it....

now I could the same piece of code with minor changes 1000 times or I could do

for($i=0;$i<1000;$i++)
  validate_my_data($data_to_validate,$array_with_pointers_to_database_locations[$i]);

that replacing endless lines of

$result = mysql_query('SELECT * FROM table WHERE column=location1');
$row = mysql_fetch_assoc($result);
if($row['data_to_validate'] == $good)
  echo 'Its good!';
else
  echo 'Its not good!';
$result = mysql_query('SELECT * FROM table WHERE column=location2');
$row = mysql_fetch_assoc($result);
if($row['data_to_validate'] == $good)
  echo 'Its good!';
else
  echo 'Its not good!';
$result = mysql_query('SELECT * FROM table WHERE column=location3');
$row = mysql_fetch_assoc($result);
if($row['data_to_validate'] == $good)
  echo 'Its good!';
else
  echo 'Its not good!';

now which would you prefer to write? 😉

mrfritz379

Another major bonus of using a function is passing the variables. Imagine you do have 100 different mathematical formula pages you need to write. Each of them would have to have the same variable $x for the addition or subtraction, the same variable $y for division or multiplication or whatever.
Then what happens when you're pulling in user information from a form? You can't name everything $x and $y.
It's much simpler to include 1 page of functions that has:

function addNumbers($x,$y){ 
   $NuNum = $x+$y; 
   return $NuNum; 
}

mrfritz379

I will say, though, that I am extremely confused on the whole subject of Object Orientation. Really, what's the main bonus of using classes as opposed to individual functions.
I'm new to the whole programming world- PHP is my first language and I've only been coding for about 8 or 9 months, so I don't have the experience with C++ or JavaScript that are heavily object oriented (so I hear), so I have a hard time wrapping my mind around the concept.
Is there really a bonus to typing:

$table = $dom->create_element("table");
$table = $body->append_child($table);
$table->set_attribute('width', '100');
$table->set_attribute('border','0');
$table->set_attribute('cellspacing','0');

when you can just type

$table = "<table width=\"100\" border=\"0\" cellspacing=\"0\">";

tekky

the big thing with objects are they are reusuable... once you design an object class once.... you never have to retype that code....

take a message board for example in a text based game... they are excellent examples in my opinion.... you have 30 different groups in this game.... each has their own board... now do you copy the board.php file to each of the directories for those groups or do you make a class that you can just do board->create("group1"); board->create("group2"); etc etc and your 1 class file is able to replicated 30 boards and keep them seperated via board ids....

thats the kind of things that OOP is good for, its like taking the redundancy that functions are able to eliminate to the 2nd power 😉

mrfritz379

Originally posted by tekky
you make a class that you can just do board->create("group1"); board->create("group2"); etc etc and your 1 class file is able to replicated 30 boards and keep them seperated via board ids....

I can see how that is beneficial, but couldn't you do the something with some kind of multi-dimensional array?

I don't know, maybe my big problem is that I've never been in a scenario where I've had to call multiple instances of a class. I've done some experimenting with OOP, but I always just end up calling the class one time, and the class definition is usually not that usable in other scripts. I guess I'm not thinking abstract enough...

Drakla

Functions and classes remote 'fiddlyness' from your code and make it more readable - and believe me, when you're working on something substantial readability is important.

For example, I never use the build in mysql commands any more, with their result handles and connection handles - too much mess. I've written a class that handles all that internally so

$query = "SELECT SOMETHING....";

$res = mysql_query($query, $dbHandle);

If (!$res)
{
    echo 'MYSQL FAILURE On query: ', $query, '<br />', mysql_error();
    exit;
}

while ($row = mysql_fetch_assoc($res))
{
    // your stuff
}

Becomes

$q = "SELECT SOMETHING...";

$db->safe_query($q);

while ($row = $db->fetch_assoc())
{
    // your stuff
}

Objects are great for encapsulation. When I was videogame programming I had to do stuff with missiles following paths leaving flame trails that were animations (each starting at different stages) - when a missile hit something (it would check itself as every object in the game has an action() function that was different for each type of object) then it would kill itself and create 100 or so particle effect objects and a central explosion... each of those resposible for their trajectory and lifetime.

Doing that without objects would be an absolute nightmare.

laserlight

What's the point of creating your own functions when you can just use include statements instead?

1. Using include means reading a file, and file operations are expensive.
Grouping several (especially related) functions for a single include call means you read less files.

If one would replace an extensive function library with include files, then the separate include files would clutter the filesystem, being many.
There are cases where one might need functions to implement a technique, e.g. recursion where eliminating it would increase the complexity of the code greatly, perhaps by having to re-implement a stack.
Variables (aside from the superglobal arrays and those declared global) are in a local scope within functions.
This locality of scope does not exist in an included file, and hence increases the risk of variables getting used/modified where they shouldnt.
Passing values to include files requires defining variables in the caller.
On the other hand, it is often possible to call a function as an argument to another function, and this elimates the step of storing the intermediate result in a variable.