functions

MysticFallout

im having problems understanding how to use functions. not the premade ones like main and those, but ones i would write.

ones like this i understand

function write_it()
echo "hey";
}

write_it();

(should work i think L)

but like when i want to do something, like update a file or something. i would write the function block with all the code in it and call it how? with a form? i just havent been able to find out anything at all really pertaining to this. cause that above could be done with an if_else block easier (right?)

any info on using functions is greatly apreciated.

rebelo

Well, they are pretty straight forward. You have the right idea with your example, you just need to take it further. Lets do the same thing, but say we want to write the string to a file instead of printing to screen, and also lets say that the string is set by a user in a form and the form field is called "input". You would do something like this (please no barking about syntax etc, im just demonstrating):

// i will skip error traps for brevity

function write_string($input)
{
 global $file, $permissions;
 $fp = fopen($file, $permissions);
 if(fwrite($string, $fp))
 {
  return true;
 }else{
  return false;
 }
}

if(isset($input))
{
 // input is set, write it to the file
 if(write_string($input))
 {
  echo "Success";
 }else{
  echo "failure";
 }
}

sfhc

Functions like the one rebelo posted are called like this in php

write_string($string);

So if you did have a form,

what ever script that the form went to would have

write_string($sting);

function write_string($string){
.....
}

Bunkermaster

why make a function when you can code the same thing hundreds of time.... hmmm

a good rule to follow is this :

if you copy paste in your code ask yourself if you couldn't have refactored more efficiently. The maintenability of code is always a major issue in software development and normally represents more than 50% of the cost.

if you have a bug that is repeated in your scripts tens of times you'll have to fix it in every instance of it and murphy says you'lll fail

🙂

7khat

Any variable you want your function to use you need to declare as an attribute in the normal brackets.

For example:
/////
function product ($a, $b) {
$result = $a * $b;
return $result;
}
/////

You can call the function like this:

/////
$p = product(5, 3);
print $p;
/////
15 will be printed

Or like this:

/////
$a = 5;
$b = 3;
$p = product($a, $b);
print $p;
/////
15 will be printed

Note that all variables inside the functions are different to the ones outside of the functions. This is correct for other functions as well.

So we can have:

/////
$result = "Old data";
$a = 5;
$b = 3;
$p = product($a, $b);
print $p;
print $result;
/////
15 will be printed, then "Old data" will be printed (sans quotation marks). The $result INSIDE the function will not overwrite the $result OUTSIDE the function.

Now if you want your function to share some variables with the outside world, you can tell it to do so like this:

/////
function product ($a, $b) {
global $c;
$result = $a * $b + $c;
return $result;
}
/////

Looking back at our script, we can do this:

/////
$a = 5;
$b = 3;
$c = 10;
$p = product($a, $b);
print $p;
/////
25 will be printed, as the function will read $c from outside. However, do this sparingly as making things GLOBAL can be both a security threat and it can intefere with other fuctions and be rather hard to trace, if it causes problems. Make sure you know at all times what variables you are making GLOBAL.

Variables you have "defined" will be read inside functions by default.
Like things you have made with:
define ('MAIN_TABLE', 'main');
can be read inside functions right off the bat.

Another nifty basic thing you can do with functions is this:

/////
function product ($a, $b=2) {
$result = $a * $b;
return $result;
}
/////
Notice I put $b=2 in the first line of the function. This forces the function to assign $b to be 2 as a default.
With the old fuction if you called it like this:
$p = product($a);
Then php will whinge about "expecting another parameter for product".

With the new function $b will become 2 if the script did not provide a variable to set $b.
/////
$a = 5;
$b = 3;
$p = product($a);
print $p;
/////
10 will be printed.
Assigning defaults to your attributes is a good habit, and have proven to save me some time, both in troubleshooting and in function usage.

greg252

I recently wrote a function to generate a calendar which takes 1 argument- the month you want to generate a calendar for.

I wrote the function once and call it using
calendar($month);
where the month does not have to be THIS month. It could be last month, the month before that or any month after this month (you get the idea)

By using a function, I don't have to keep re-writting the same thing over and over.

7khat

I use stacks and stacks of functions

rebelo

Originally posted by 7khat
I use stacks and stacks of functions

Likewise. I also usually put them in an include.php file or something similar and then include them into all the pages in my site so that adding a function to the library lets me access it from all pages in the site.