if
At Caliban Darklock
I don't know if it is just improvements in the parser, but there is a negligible difference in the performance of "elseif" vs "else if" as of version 5. One thousandth of a second in your example and 8 thousandths if the eval statement is repeated 5 times.
If the constructs are in regular code, then there appears to be no difference. This leads me to believe that the difference in the eval code is from there being an extra parser token.
Also the main performance burden of recursive functions is the stack operations of changing the context. In this case I believe that it would parse to very similar (if not identical) jmp controls.
In summary, use your preference. Readability and maintainability rank far higher on the priority scale.
One Additional note, there appears to be a limit of the number of "else if" statements (perhaps nested statements in general) that php will handle before starting to get screwy. This limit is about 1100. "elseif" is not affected by this.
else
Souvent, vous voulez exécuter une instruction si une
condition est remplie, et une autre instruction si cette condition
n'est pas remplie. C'est à cela que sert else.
else fonctionne après un
if et exécute les instructions
correspondantes au cas oú l'expression du if
est FALSE. Dans l'exemple suivant, ce bout de code
affiche a est plus grand que b si la
variable $a est plus grande que la variable
$a, et a est plus petit que b
sinon :
Exemple #1 Instruction if () else
Les instructions après le else ne sont
exécutées que si l'expression du if
est FALSE, et si elle n'est pas suivi par l'expression
elseif - uniquement si elles sont évaluées à FALSE (voir elseif).
<?php
if ($a > $b) {
echo "a est plus grand que b";
} else {
echo "a est plus petit que b";
}
?>
add a note
User Contributed Noteselse
Theoden
25-Apr-2008 01:42
25-Apr-2008 01:42
dormeydo at gmail dot com
12-Apr-2008 12:51
12-Apr-2008 12:51
An alternative and very useful syntax is the following one:
statement ? execute if true : execute if false
Ths is very usefull for dynamic outout inside strings, for example:
print('$a is ' . ($a > $b ? 'bigger than' : ($a == $b ? 'equal to' : 'smaler than' )) . ' $b');
This will print "$a is smaler than $b" is $b is bigger than $a, "$a is bigger than $b" if $a si bigger and "$a is equal to $b" if they are same.
mitch at mitchellbeaumont dot com
24-Jul-2007 08:09
24-Jul-2007 08:09
At gwmpro at yahoo dot com
The curly brace is not required however, for readability and maintenance, many developers would consider it bad style not to include them.
Caliban Darklock
08-Nov-2004 07:24
08-Nov-2004 07:24
If you're coming from another language that does not have the "elseif" construct (e.g. C++), it's important to recognise that "else if" is a nested language construct and "elseif" is a linear language construct; they may be compared in performance to a recursive loop as opposed to an iterative loop.
<?php
$limit=1000;
for($idx=0;$idx<$limit;$idx++)
{ $list[]="if(false) echo \"$idx;\n\"; else"; }
$list[]=" echo \"$idx\n\";";
$space=implode(" ",$list);| // if ... else if ... else
$nospace=implode("",$list); // if ... elseif ... else
$start=array_sum(explode(" ",microtime()));
eval($space);
$end=array_sum(explode(" ",microtime()));
echo $end-$start . " seconds\n";
$start=array_sum(explode(" ",microtime()));
eval($nospace);
$end=array_sum(explode(" ",microtime()));
echo $end-$start . " seconds\n";
?>
This test should show that "elseif" executes in roughly two-thirds the time of "else if". (Increasing $limit will also eventually cause a parser stack overflow error, but the level where this happens is ridiculous in real world terms. Nobody normally nests if() blocks to more than a thousand levels unless they're trying to break things, which is a whole different problem.)
There is still a need for "else if", as you may have additional code to be executed unconditionally at some rung of the ladder; an "else if" construction allows this unconditional code to be elegantly inserted before or after the entire rest of the process. Consider the following elseif() ladder:
<?php
if($a) { conditional1(); }
elseif($b) { conditional2(); }
elseif($c) { conditional3(); }
elseif($d) { conditional4(); }
elseif($e) { conditional5(); }
elseif($f) { conditional6(); }
elseif($g) { conditional7(); }
elseif($h) { conditional8(); }
else { conditional9(); }
?>
To insert unconditional preprocessing code for $e onward, one need only split the "elseif":
<?php
if($a) { conditional1(); }
elseif($b) { conditional2(); }
elseif($c) { conditional3(); }
elseif($d) { conditional4(); }
else {
....unconditional();
....if($e) { conditional5(); }
....elseif($f) { conditional6(); }
....elseif($g) { conditional7(); }
....elseif($h) { conditional8(); }
....else { conditional9(); }
}
?>
The alternative is to duplicate the unconditional code throughout the construct.