Help undestanding return

CazadorDeSue__os

Hi to everyone.

I'm having trouble undestanding the return function (or language construct if you want)

for instance:

<?php

function something()
{
    $var = "something";
    return $var;
}

?>

i understand that, the problem is when the function says return false, return true or just return alone, even i've seen some functions that have a return -1 :queasy: . I mean i know that it returns a boolean, but how do i use that then 😕

Obviously i also have problem undestanding when the function have multiple return's, that really goes way over my head :o

So, if anyone can help through this it will be very appreciated.

Cheers.

laserlight

In PHP, functions may return values of any type, or none at all, or even of mixed types.
Functions may only return one value (though it may be an array), so somewhere in the logic, you can trace it to only one return point.

You can use the return value directly by using the function directly, or use it by first assigning it to a variable.

For example:

<?php

function something()
{
    $var = "something";
    return $var;
}

//use the function directly
echo something();

//assign the value returned by something() to $foo
$foo = something();
//now use $foo
echo $foo;
?>

CazadorDeSue__os

Uhmmm thanks, but i said in my first post that i understand that.

What i do not undestand is for instance (function taken from phpB😎

function obtain_word_list(&$orig_word, &$replacement_word)
{
	global $db;

//
// Define censored word matches
//
$sql = "SELECT word, replacement
	FROM  " . WORDS_TABLE;
if( !($result = $db->sql_query($sql)) )
{
	message_die(GENERAL_ERROR, 'Could not get censored words from database', '', __LINE__, __FILE__, $sql);
}

if ( $row = $db->sql_fetchrow($result) )
{
	do 
	{
		$orig_word[] = '#\b(' . str_replace('\*', '\w*?', phpbb_preg_quote($row['word'], '#')) . ')\b#i';
		$replacement_word[] = $row['replacement'];
	}
	while ( $row = $db->sql_fetchrow($result) );
}

return true;
}

That return true..... What do i do with that outside the function ?? and what if it is a return false or just plain return

And the other thing is when function have multiple returns (function taken from phpbb)

function get_db_stat($mode)
{
	global $db;

switch( $mode )
{
	case 'usercount':
		$sql = "SELECT COUNT(user_id) AS total
			FROM " . USERS_TABLE . "
			WHERE user_id <> " . ANONYMOUS;
		break;

	case 'newestuser':
		$sql = "SELECT user_id, username
			FROM " . USERS_TABLE . "
			WHERE user_id <> " . ANONYMOUS . "
			ORDER BY user_id DESC
			LIMIT 1";
		break;

	case 'postcount':
	case 'topiccount':
		$sql = "SELECT SUM(forum_topics) AS topic_total, SUM(forum_posts) AS post_total
			FROM " . FORUMS_TABLE;
		break;
}

if ( !($result = $db->sql_query($sql)) )
{
	return false;
}

$row = $db->sql_fetchrow($result);

switch ( $mode )
{
	case 'usercount':
		return $row['total'];
		break;
	case 'newestuser':
		return $row;
		break;
	case 'postcount':
		return $row['post_total'];
		break;
	case 'topiccount':
		return $row['topic_total'];
		break;
}

return false;
}

Why the 2 return false ?

Cheers

czambran

On the first script it returns true to let you know that It did the word replacement with out a problem. In this case from what I can see I could have as well just return without any value, but using a boolean is always helpful so that u can use it on a loop.

the second script has 2 returns with a false value and 4 with other values. The false values are either because as on the first script it couldn't execute the sql statement or the "mode"(parameter) is not a valid one.

Hope it makes it a little bit clearer.

laserlight

I would suggest that you learn using simpler scripts.
phpBB is a complex forum, and its code structure would be very difficult to understand when you're still struggling with the basics.
Later, when you are better equipped, you should then come back and analyse the code of phpBB.

Anyway:
obtain_word_list() returns true if nothing goes wrong.
This true value is a status code that tells (or can tell) the main script (or rather the 'caller', i.e. the code portion that called (or invoked) this function) whether or not it is successful.
If it is not successful, obtain_word_list() does not return a false value (or any value at all, apparently).
Rather, it invokes the message_die() function, which presumably is some user defined error handling function that gracefully prints an error message to the phpBB user, and then ends the script.
Since the script ends here (if unsuccessful), it then could be the reason why obtain_word_list() does not return a value if unsuccessful - it would never get the chance anyway.

For the next function:
There are multiple return values, but only one is used for each invocation of the function.
Consider:

    if ( !($result = $db->sql_query($sql)) )
    {
        return false;
    }

If $db->sql_query($sql) returns a false value, the function returns false.
It returns false to the caller, hence passing control back to the caller.
This means that the rest of the function is not evaluated, hence the next return statement is never used.

On the other hand, if $db_query($sql) returns a true value, control bypasses this return statement, and so the next return statement is eventually reached.

CazadorDeSue__os

Thanks czambran.

And specially thanks to laserlight for that really easy to understand explanation, you rock. 😉

Cheers.