PHP Reference

[perryc]

Can someone help me with passing functions by reference in php. having a hard time trying to get a grasp around the idea of reference's and what i would use them for in everyday php coding.

 

 

Thanks,

 

 

 

 

Cody Perry

[falkencreative]

Pass by value looks like this:

 

<?php

function test($temp)
{
   $temp++;
}

$i = 0;
test($i); 
echo $i;  // displays "0"

?>

 

There's no connection between the $temp variable within the function and the $i variable outside, so echoing out $i results in "0". $temp only exists within the test() function and disappears once the function ends.

 

Here's pass by reference:

 

<?php

function test(&$test)
{
   $test++;
}

$i = 0;
test($i);
echo $i; // displays "1"

?>

 

Note the "&" before the variable name in test(&$test). That means that when you pass in the variable, rather than creating a brand new variable, $temp references the $i variable outside the function. Any changes made to $temp within the function will also affect $i.

 

How is this helpful? I'm not sure, it depends on what you need coded. I've really never used it in my PHP code (yet, at least) but I have used it quite often in C++.

 

It has come in handy for me on several occasion. For example, consider this situation... You have a function that should return a valid integer (0 through whatever). However, there is also a chance that the number you are looking for doesn't exist. How do you code your function? If the variable doesn't exist and the function fails, you can't return 0 (false), since that is a valid integer and could be confused.

 

However, you could do something like this:

 

<?php

function get_variable($temp)
{
  if (variable exists)
  {
     $temp = variable;
     return true;
  }
  else
  {
     return false;
  }
}

$i = '';
if (get_variable($i))
{
  // get_variable() returns true
  // $i will contain the variable you were looking for
}
else
{
  // get_variable() returns false
  // $i still contains ''
}

?>

 

Does that make a bit more sense?

[perryc]

A little bit the way the book explains the example is like a matchbox with a string attached to it I got real confused at first. Then i went back and read the information step by step. So i understand it a little bit better now. Im learning Including and Requiring files section on my chapter right now so hopefully i don't have any more trouble with this chapter i fell real stupid sometimes asking questions like these to you guys. Thanks,

 

 

 

 

 

Cody Perry

[falkencreative]

fell real stupid sometimes asking questions like these to you guys.

Better that you ask questions and feel a little silly but get a better understanding of the concepts than to not ask questions and not understand at all. Feel free to ask questions - that's what we are here for.

[perryc]

Lol, thanks. Ya im hoping i can finishes this book by my birthday which is this friday. Then i have a more advanced php book then lol. Thanks.

 

 

 

 

 

Cody Perry