[RESOLVED] Using Return

edziffel

Been trying to figure out what is going on with the return.

The manual says:
If called from within a function, the return() statement immediately ends execution of the current function, and returns its argument as the value of the function call. return() will also end the execution of an eval() statement or script file.

Other searches say pretty much the same thing. My problem is that I'm not getting what is meant by "returns its argument as the value of the function call".

For isntance

  function mysql_field_array( $result ) {

    $field = mysql_num_fields( $result );

    for ( $i = 0; $i < $field; $i++ ) {

        $names[] = mysql_field_name( $result, $i );

    }

    return $names;

}

So I get that the array $names is populated by using $i as index values and the value for $names[$i] is the value of mysql_field_name for the current parameters $result ,$i. So far so good.
But return $names; return to where? and how do you access it? Now that it has neatly been returned, what do you do with it? And what good is it/why is it helpful?

laserlight

edziffel wrote:
But return $names; return to where?

To the caller. For example, you might have written:

$field_names = mysql_field_array($result);

edziffel wrote:
and how do you access it?

Referring to my example line of code, you would then access the $field_names variable.

edziffel wrote:
Now that it has neatly been returned, what do you do with it?

It depends on what is it for. For example, you might use $field_names to help print the headers for a table in which the results are to be displayed.

edziffel wrote:
And what good is it/why is it helpful?

If you are talking about return statements in general, then the answer is: it is good and helpful because it provides a way to obtain a result from a function.

edziffel

Thank you for the response.

Sitll a bit fuzzy...

Quote:
Originally Posted by edziffel
But return $names; return to where?
To the caller. For example, you might have written:
PHP Code:
$field_names = mysql_field_array($result)

;

What is returned? The code execution sequence back to the original function or the value of the executed function to .... what, the argument $result?. And if the first is true, then isn't that an endless loop? And if the second is true same question? Of course the endless loop thing can't be true just using common sense. I have to have a concept issue here huh?

PHP Code:
$field_names = mysql_field_array($result);
Quote:
Originally Posted by edziffel
and how do you access it?
Referring to my example line of code, you would then access the $field_names variable.

Couldn't you just access the $field_names variable anyway without using return?

Quote:
Originally Posted by edziffel
And what good is it/why is it helpful?
If you are talking about return statements in general, then the answer is: it is good and helpful because it provides a way to obtain a result from a function.

Again can't you just access the results through the $feild_names variable? So why not just save the space and skip the return thing?

As you no doubt can tell, I'm not getting it. lol

laserlight

edziffel wrote:
What is returned? The code execution sequence back to the original function or the value of the executed function to .... what, the argument $result?.

The result of evaluating the expression in the return statement is returned. In this case, that would be the array referred to by $names. Since the result of the function is assigned to $field_names, we can say that for this particular call of the function, it returns to $field_names. It certainly does not return to the argument, unless the variable passed as the argument happens to be the variable used to store the result of the calling the function.

edziffel wrote:
Couldn't you just access the $field_names variable anyway without using return?

edziffel wrote:
Again can't you just access the results through the $feild_names variable? So why not just save the space and skip the return thing?

I gather that when you bake cookies, you put the cookies into the oven, and then after baking you eat the cookies without removing them from the oven 😉
After all, can't you just stick your head into the oven and bite from there? Why not just save the space and skip moving the tray to a table or moving the cookies to a plate?

edziffel

Quote:
Originally Posted by edziffel
What is returned? The code execution sequence back to the original function or the value of the executed function to .... what, the argument $result?.
The result of evaluating the expression in the return statement is returned. In this case, that would be the array referred to by $names. Since the result of the function is assigned to $field_names, we can say that for this particular call of the function, it returns to $field_names. It certainly does not return to the argument, unless the variable passed as the argument happens to be the variable used to store the result of the calling the function.

Okay. I can play with that to check how all that happens, print_r and such. Got it.

I gather that when you bake cookies, you put the cookies into the oven, and then after baking you eat the cookies without removing them from the oven
After all, can't you just stick your head into the oven and bite from there? Why not just save the space and skip moving the tray to a table or moving the cookies to a plate?

The old bobbing for 350 deg F cookies on a hot tin tray trick. The thing is to be first so you can get the ones in front. lol

So the return more or less just terminates the function, possibly assigning the evaluated result to a new variable, and then life as a php script continues as normal. Is that a fair assessment?

NogDog

In a way, the term "return" can use two of its possible meanings in this context.

(a) It returns control from the function back to the code that called the function, which also effectively terminates that function (nothing after the "return" will be processed within that function).

(b) It optionally, if provided, returns something back to the calling code -- which I guess is actually a bit of a misnomer, as "return" would imply that the calling code "gave" it something. That something can then either be assigned by the calling code to a variable, used as an expression of some sort in another context (e.g. a parameter for another function or text to be output by an echo statement), or completely ignored.

$var = myFunction();  // whatever is returned is assigned to $var
anotherFunction(myFunction()); // whatever is returned is used by another function
echo myFunction();   // whatever is returned is immediately echoed
myFunction();       // whatever is returned is ignored and lost into a data black hole

edziffel

Thanks laserlight and nogdog.

Have a clear idea now. The biggest reason form my confusion is at the moment return() doesn't appear to do anything that cant be done with out it.

Now that I've said it, something will probably come up where return() will be just the ticket. Have not been using PHP all that long so it would be so it would be presumptuous to just rule it out, so will keep it under my hat.

Thanks again,

leatherback

Hi Edd, I think you are missing some critical points of information:

Variable scope: A variable that 'lives' in a function, is not available outside the function. Try this:

function SetA($value)
  {
  $a = $value;
  return($a);
  }

$a = '';
$b = SetA(9);

echo "a is now: ". $a "--<br />";
echo "b is now: ". $b "--<br />";

This is why you need the return. $a in the main script is not affected by whatever we did in the function.

Then, why go through the hassle of writing a function?
Consider you have 5 pages, each of which needs to get a menu. The menu is based on a call to the database, with settings sepcific for the page you are on. So you could in theory use a script which you copy into each page (Or better: include on each page). However, that would require you to use exactly he same variable names on each page, which is not alway usefull. Of, you could create a function, build_menu(), which takes a number of arguments (Such as an array with menu items, their status and link). The latter would make your code easier to read (After all, you can tell exactly where the menu is forme, and which data was used as input). Also, it makes it easier to re-use code over and over again in the same page.

For instance: I wrote a script 'get_variable'. This script checks the POST array and the GET array whether a variable is set. Then I have told the script to find an stringarray, a numeric array, a string or a number as a value. If the variable does not match the content I expect, it sets a default value. All in all, some 20 lines of code. So now, if I want to grab variables which may be passed by a form OR by a URL reference, I just go:

== function get_variable($label, $type, $default) ==

$variable = get_variable('SomeName', 1, '');
$variable2 = get_variable('SomeName2', 1, '');
$variable3 = get_variable('SomeName3', 1, '');

And my variables are verified, secured for further queries and I am ready to go.

edziffel

Hi leatherback.

First let me thank you (et al) for all the help. Would be up the creek with no paddle with out it. Seriously makes a difference for me.

On the return thing:

Still not feeling it. Use testing and specific coding methodology to resolve scope issues. But...

When all the good old boys and girls, and we are talking 100% in this case, are solidly behind something, rookies (me) fail to take heed at their own peril. Moving it from under the hat to watch for it. : - )