Kontroll-Strukturen
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
Häufig möchten Sie eine Anweisung auszuführen, wenn eine
bestimmte Bedingung erfüllt ist und eine andere Anweisung, falls
sie nicht erfüllt ist. Dafür gibt es else.
else erweitert eine if-Anweisung um
die Ausführung von Anweisungen, sobald der Ausdruck der
if-Anweisung als FALSE ausgewertet wird. Der folgende
Code wird z.B. a ist größer als b
ausgeben, wenn $a größer als $b ist,
anderenfalls a ist NICHT größer als b:
Die else-Anweisung wird nur ausgeführt, wenn
der if-Ausdruck als FALSE
ausgewertet wurde und wenn bei vorhandenen
elseif-Ausdrücken diese ebenfalls
FALSE sind (siehe elseif).
<?php
if ($a > $b) {
print "a ist größer als b";
} else {
print "a ist NICHT größer als b";
}
?>
add a note
User Contributed Noteselse
Theoden
24-Apr-2008 05:42
24-Apr-2008 05:42
dormeydo at gmail dot com
12-Apr-2008 04:51
12-Apr-2008 04:51
An alternative and very useful syntax is the following one:
statement ? execute if true : execute if false
Ths is very usefull for dynamic outout inside strings, for example:
print('$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 12:09
24-Jul-2007 12:09
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 11:24
08-Nov-2004 11:24
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.