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PHP : Language Reference : Control Structures : switch

switch

The switch statement is similar to a series of IF statements on the same expression. In many occasions, you may want to compare the same variable (or expression) with many different values, and execute a different piece of code depending on which value it equals to. This is exactly what the switch statement is for.

Note:

Note that unlike some other languages, the continue statement applies to switch and acts similar to break. If you have a switch inside a loop and wish to continue to the next iteration of the outer loop, use continue 2.

Note:

Note that switch/case does loose comparision.

The following two examples are two different ways to write the same thing, one using a series of if and elseif statements, and the other using the switch statement:

Example7.1.switch structure

<?php
if ($i == 0) {
echo
"i equals 0";
} elseif (
$i == 1) {
echo
"i equals 1";
} elseif (
$i == 2) {
echo
"i equals 2";
}

switch (
$i) {
case
0:
echo
"i equals 0";
break;
case
1:
echo
"i equals 1";
break;
case
2:
echo
"i equals 2";
break;
}
?>


Example7.2.switch structure allows usage of strings

<?php
switch ($i) {
case
"apple":
echo
"i is apple";
break;
case
"bar":
echo
"i is bar";
break;
case
"cake":
echo
"i is cake";
break;
}
?>


It is important to understand how the switch statement is executed in order to avoid mistakes. The switch statement executes line by line (actually, statement by statement). In the beginning, no code is executed. Only when a case statement is found with a value that matches the value of the switch expression does PHP begin to execute the statements. PHP continues to execute the statements until the end of the switch block, or the first time it sees a break statement. If you don't write a break statement at the end of a case's statement list, PHP will go on executing the statements of the following case. For example:

<?php
switch ($i) {
case
0:
echo
"i equals 0";
case
1:
echo
"i equals 1";
case
2:
echo
"i equals 2";
}
?>

Here, if $i is equal to 0, PHP would execute all of the echo statements! If $i is equal to 1, PHP would execute the last two echo statements. You would get the expected behavior ('i equals 2' would be displayed) only if $i is equal to 2. Thus, it is important not to forget break statements (even though you may want to avoid supplying them on purpose under certain circumstances).

In a switch statement, the condition is evaluated only once and the result is compared to each case statement. In an elseif statement, the condition is evaluated again. If your condition is more complicated than a simple compare and/or is in a tight loop, a switch may be faster.

The statement list for a case can also be empty, which simply passes control into the statement list for the next case.

<?php
switch ($i) {
case
0:
case
1:
case
2:
echo
"i is less than 3 but not negative";
break;
case
3:
echo
"i is 3";
}
?>

A special case is the default case. This case matches anything that wasn't matched by the other cases. For example:

<?php
switch ($i) {
case
0:
echo
"i equals 0";
break;
case
1:
echo
"i equals 1";
break;
case
2:
echo
"i equals 2";
break;
default:
echo
"i is not equal to 0, 1 or 2";
}
?>

The case expression may be any expression that evaluates to a simple type, that is, integer or floating-point numbers and strings. Arrays or objects cannot be used here unless they are dereferenced to a simple type.

The alternative syntax for control structures is supported with switches. For more information, see Alternative syntax for control structures.

<?php
switch ($i):
case
0:
echo
"i equals 0";
break;
case
1:
echo
"i equals 1";
break;
case
2:
echo
"i equals 2";
break;
default:
echo
"i is not equal to 0, 1 or 2";
endswitch;
?>

Related Examples ( Source code ) » control_structures.switch


Code Examples / Notes » control_structures.switch

dohpaz

[Editor's note: Changed the second switch to make it work as intended.]
I haven't seen anything specifically pointing this out, but you can get a small performance increase in your code by re-structuring your complex switch statements.
For example, I was using the following switch to convert textual month names into their numerical counterparts from the Date header of email on my pop server:
switch ($month_name) {
 case "Jan":
 case "January":
   $month = "1";
   break;
 ...
}
Even just looping through 15 emails on the server, it would take upwards of around 9-10 seconds! So, I decided to shorten my switch statement to something like this:
switch (TRUE) {
 case ($month_name == "Jan" || $month_name == "January"): $month = "1"; break;
 ...
}
Doing this I actually shaved 3 seconds from my script's execution time!!! I thuoght this was well worth noting for other coders out there who are looking to optimize their PHP code.


bruno feu

You can solve the problem by just writing the following piece of code:
<?php
$x = 18;
$y = 6;
switch ($x) {
  case ($y * 4):
  case (9 * 3):
      echo "Member";
      break;
  default:
      echo "Not a member";
}
?>


shawn

You can also nest switch statements inside case statements:
<?php
  // Set argument handlers
   $argv = explode(",", urldecode(getenv('QUERY_STRING')));
   $argc = array_shift($argv);
   $argd = array_shift($argv);
   $arge = array_shift($argv);
?>
  // Begin switching
<?php
   switch ($argc) {
       case 'home': {
            print('This is $argc, home case.');
           break;
       }
       case 'subsection': {
               switch ($argd) {
                    case 'links': {
                           switch($arge) {
                               case 'display': {
                               print('This is $arge, subsection,links,display case.');
                               break;
                               }
                          }
                   }
               }
       }
   }
?>


theonly dot mcseven

working a bit around with it I found out that it is not possible to
compare the variable with two different values in one step like this
(system running a w2k server, apache2.0.43 & php430):
<?php
switch ($myvar) {
case ("foo" || "bar"): //do something
break;
case ("other"): //do another thing
break;
default:
}
?>
rather use:
<?php
switch ($myvar) {
case ("foo"):
case ("bar"): //do something
break;
case ("other"): //do another thing
break;
default:
}
?>


pentek_imre

Using select is like using == (instead of ===) in an if statement. Let's see an example:
<?php
function Describe($Q)
{
 var_dump($Q);
 echo ": ";
 switch ($Q)
  {
   case "0":
    echo "String zero";
    break;
   case 0:
    echo "Integer zero";
    break;
   case NULL:
    echo "NULL NULL";
    break;
   case FALSE:
    echo "Boolean FALSE";
    break;
   case "":
    echo "Empty string";
    break;
   default:
    echo "Any other value";
    break;
  }
 echo "
\n";
}
Describe("0");
Describe(0);
Describe(NULL);
Describe(FALSE);
Describe("");
Describe(1);
?>
Output (PHP 5.0.1) is:
string(1) "0" : String zero
int(0) : String zero
NULL : Integer zero
bool(false) : String zero
string(0) "" : Integer zero
int(1) : Any other value


gray dot quinn

To get the conditional statement to work for the above example use this:
<?php
$chr = substr($a,$i,1);
switch (TRUE) {
case $chr == "á" || $chr == "à" || $chr == "ã" || $chr == "â":
$a = str_replace(substr($a,$i,1),"a",$a);
break;
case $chr == "é" || $chr == "è" || $chr == "ê":
$a = str_replace(substr($a,$i,1),"e",$a);
break;
?>
}


hexa

this is a simple function that returns a random string and uses
switch to determine what kind of string you want.
function r( [string prefix][,int type,][,int chars] );
type = 1 -> only numbers
type = 2 -> only letters
type = 3 -> both
<?php
function r($prefixo = "",$tipo = 3,$numcaracteres = 10) {
switch ($tipo) {
case 1:
for ($x = 1; $x <= $numcaracteres; $x++) {
$rnum .= chr(rand(48,57));
}
return $prefixo . $rnum;
break;
case 2:
for ($x = 1; $x <= $numcaracteres; $x++) {
if (rand(1,2) == 1) { $rletras .= chr(rand(65,90)); }
else { $rletras .= chr(rand(97,122)); }
}
return $prefixo . $rletras;
break;
case 3:
for ($x = 1; $x <= $numcaracteres; $x++) {
$r = rand(1,3);
if ($r == 1) { $rstring .= chr(rand(65,90)); }
elseif ($r == 2) { $rstring .= chr(rand(97,122)); }
else { $rstring .= chr(rand(48,57)); }
}
return $prefixo . $rstring;
break;
}
}
?>


ant

This caught me out. The number '6' when compared with the string '6b' returns true. The solution is to either typecast the compare  -  ie, " switch ((string)$type): "  or to make sure $type is a string (eg $type="6")
<?
$type=6;
switch ($type):
   case "6b":
       print "6b: ";
       print $type;
   break;
   case "6":
       print "6: ";
       print $type;
   break;
endswitch;
?>


zzo38

There is no GOTO command in PHP, but you can do something similar like this:
<?php
function testfunction($x) {$label='';while(1){switch($label){
 case '':
  if($x==0) continue ($label='fail')*0+1;
 case 'ok':
  echo "ok\n";
 case 'fail':
  echo "fail\n";
  return;
}}}
?>


hayley watson

Something not mentioned in the documentation itself, and only touched on momentarily in these notes, is that the default: case need not be the last clause in the switch.
<?php
for($i=0; $i<8; ++$i)
{
echo $i,"\t";
switch($i)
{
case 1: echo "One"; break;
case 2:
default: echo "Thingy"; break;
case 3:
case 4: echo "Three or Four"; break;
case 5: echo "Five"; break;
}
echo "\n";
}
?>
Outputs what you'd expect, namely
0       Thingy
1       One
2       Thingy
3       Three or Four
4       Three or Four
5       Five
6       Thingy
7       Thingy
with case 2 and the default both producing the same result ("Thingy"); strictly speaking, the case 2 clause is completely empty and control just falls straight through. The same result could have been achieved with
<?php
switch($i)
{
case 1: echo "One"; break;
case 3:
case 4: echo "Three or Four"; break;
case 5: echo "Five"; break;
default: echo "Thingy"; break;
}
?>
But if "case 2" represented a fairly common case (other than "everything else"), then it would be better to declare it explicitly, not only because it saves time by not having to test EVERY other case first  (in the current example, PHP finds 'case 2' in the first switch in two tests, but in the second switch it has to make four tests before giving up and going with the default) but also because someone (perhaps yourself in a few months' time) will be reading the code and expecting to see it handled. Listing it explicitly aids comprehension


ach aat bitfabrik doot de

So instead of writing the code shown below it would have to be like this:
<?php
$x = 18;
$y = 6;
switch ($x) {
  case ((($y * 4) || (9 * 3))?$x:false):
      echo "Member";
      break;
  default:
      echo "Not a member";
}
?>
So now the case expression contains an if statement in simplified notation which either returns the value of $x if the expression is true (so the case matches) or false, if the expression was false (so the case does not match).
Be aware that it only works if $x never actually is "false" because then it would match in either case. So the "false" in the above code should always be any random value which is not a possible value for $x.


jemore

siwtch() made always a type conversion before comparing all the case value (PHP4.3.0), so the following statement
<?php
     // $a = 'abc0' or 'abc1' or 'abc2', so this is a string
     switch ($a)
     {
       case 'abc0' : $nb += 1; break;
       case 'abc1' : $nb += 2; break;
       case 'abc2' : $nb += 3; break;
     }
?>
is slower than the following statement
<?
     if ($a === 'abc0') $nb += 1;
     elseif ($a === 'abc1') $nb += 2;
     elseif ($a === 'abc2') $nb += 3;
?>
because the '===' (3 equals signs) compare value without type conversion. Using a if/elseif/elseif structure instead of switch/case/case can be 2 times faster (I have made a test)


havar

Remember, that you also could use functions in a switch.
For example, if you need to use regular expressions in a switch:
<?php
$browserName = 'mozilla';
switch ($browserName) {
 case 'opera':
   echo 'opera';
 break;
 case (preg_match("/Mozilla( Firebird)?|phoenix/i", $browserName)?$browserName:!$browserName):
   echo "Mozilla or Mozilla Firebird";
 break;
 case 'konqueror':
   echo 'Konqueror';
 break;
 default:
   echo 'Default';
 break;
}
?>
or you could just use a regular expression for everything:
<?php
$uri = 'http://www.example.com';
switch (true) {
 case preg_match("/$http(s)?/i", $uri, $matches):
   echo $uri . ' is an http/https uri...';
 break;
 case preg_match("/$ftp(s)?/i", $uri, $matches):
   echo $uri . ' is an ftp/ftps uri...';
 break;
 default:
   echo 'default';
 break;
}
?>


phpmanual

Regarding bishop's comment below, although using:
  switch($bug === 0 ? '' : $bug) {
may work, ( and although I do like the ternary operator, :) it might be more intuitive/readable to use this instead:
  switch( (string)$bug ) {
which typecasts the variable to a string to ensure that "0" will be handled correctly.


turk162

On PHP V4.2.1, running on IIS5 as a CGI, I found an anomaly with how SWITCH handled strings.  I've heard that this problem doesn't exist on V4.2.3 on Apache.
This snippet took the wrong branch:
<?PHP
$wonum = '20010E0';
SWITCH ($wonum):
  CASE '20010D0';
     ECHO "
Branching at D with wonum: " . $wonum;
     BREAK;
  CASE '20010E0';
     ECHO "
Branching at E with wonum: " . $wonum;
     BREAK;
ENDSWITCH;
?>
Type casting with $wonum = (STRING) '20010E0'; didn't help.
Changing the order of the CASEs made no difference (it shouldn't, but...)
What did work was using MD5 to force a string comparison:
<?PHP
$wonum = MD5('20010E0');
SWITCH ($wonum):
  CASE MD5('20010D0');
     ECHO "
Branching at D with wonum: " . $wonum;
     BREAK;
  CASE MD5('20010E0');
     ECHO "
Branching at E with wonum: " . $wonum;
     BREAK;
ENDSWITCH;
?>
Moral: test test test


x@x

often you will have to perform multiple actions in sequence, but this sequence must be broken once one of them detects a stop condition (such as an error, when validating form request variables).
One way is to use:
if (check1()
&& check2()
&& check3()
) valid();
else error();
But when the sequence is long and must reordered, this can be errorprone because not all line of check have the same syntax (imagine that you want to comment one of them).
Another way is to rewrite it as:
check1() and
check2() and
check3() and
...
valid() or
error();
The above syntax does not fit well when the valid() code must be several statements.
An alternative syntax can be:
switch (false) {
case check1():
case check2():
case check3():
  error();
  break;
default:
  valid();
}
This last equivalent sample show you that each case expressions is evaluated, until one of them evaluates to a value equal (==) to the switch expression. Above, the error() code will only be called if one of the check evaluates to false. And the valid() code will only be evaluated only if the switch reach the default, which means that none of the above check returned false...


i luv spam

Noticed some odd switch behavior worth mentioning:
Switching on a variable set as $var="08" and forgetting the quotes within the case results in different behavior depending on the two digit number the variable is set to.
For "01" to "07", using a case like
 case 01:
the case is triggered.
For "08" or "09" the case is skipped.
For "10" to "12" the case is triggered.
Looks like something octal may be going on.
Anyway, not a problem once the case is changed to:
 case "08":
as it should have been from the start.  Just odd.


kriek

Nice, clean, template style navigation. In most cases it is fifteen percent faster to use switch/case/break instead of if/elseif/else. Of course this depends on your application and individual code results do very.
<?php
   switch ($_GET['go']) {
       case "1": $inc = 'Page01.php';
       break;
       case "2": $inc = 'Page02.php';
       break;
       case "3": $inc = 'Page03.php';
       break;
       case "4": $inc = 'Page04.php';
       break;
       default: $inc = 'Page01.php';
       break;
   }
   include ($inc);
?>


cgibbard student math uwaterloo ca

Just in reply to the comment about 2 digit numbers: something octal certainly is going on. Integer literals prefixed with a "0", like in C and several other languages, are treated as octal. Similarly, integer literals prefixed with "0x" are treated as hexadecimal. Seeing as this is the case, 08 and 09 are not valid integer literals. It turns out that php treats them as 0 (it would probably be better to fail with an error message, but it doesn't). Bottom line? Don't prefix numbers with 0 in code unless you mean octal. Format them as you print them with printf, like so: printf("%02u", $my_unsigned_int); or if you will, use sprintf to get a string representation rather than printing on stdout.

nospam

Just a trick I have picked up:
If you need to evaluate several variables to find the first one with an actual value, TRUE for instance. You can do it this was.
There is probably a better way but it has worked out well for me.
switch (true) {
 case (X != 1):
 case (Y != 1):
 default:
}


stever

Just a reminder: there may be easier ways to manipulate _long_ lists of data instead of using switches.
function getChineseZodiac($year){
 
 // Chinese Zodiac Animals
 $animals = Array
 (
   'Monkey',  // Years 0, 12, 1200, 2004...
   'Rooster',
   'Dog',
   'Boar',
   'Rat',
   'Ox',
   'Tiger',
   'Rabit',
   'Dragon',
   'Snake',
   'Horse',
   'Lamb'
 );
 // Number of animals and years in a calendar rotation
 $numAnimals = count($animals);
 // Years left until full rotation of calender
 $yearOffset= round($year) % $numAnimals;
 
 return $animals[$yearOffset];
 
}
Of course this is a really generic function, we're just finding how many years away from a full 12 year rotation the current year is.


rtreat2

just a further example of the above note, you can do the following type of searching:
<?php
switch (true){
   case ( ereg ("stats",$userfile_name) ):
       echo "processing stats";
       process_stats();
       break;  
   case ( ereg("prices",$userfile_name) ):
       echo "processing prices";
       process_prices();
       break;  
   default:
       echo = "File not recognized!!.";
}
?>
this script could be used to determine data formats for uploaded files based on a nameing conve
ntion. just one example.


bensphpnetemail

It's obvious, but might still bear explicit mention that you can conditionally execute the BREAK statement in order to allow a CASE to fall through to the next CASE.  
e.g.:-> Here, CASE 1 will fall through and the DEFAULT CASE statements will also be executed unless $somevar is true.
<?php
switch ($i) {
   case 0:
       print "i equals 0";
       break;
   case 1:
       print "i equals 1";
       if ($somevar) {
            break;
            }
   default;
      echo 'Some Default Statements';
       break;
}
?>
Cheers,
Ben Nardone


scott

It's has already been mentioned indirectly in a few posts, but it is important to realize that switch statements evaluate each case with the "==" operator by default. This can lead to unexpected results when comparing strings to integers, because PHP will convert the string to an integer. In many cases this means a string can be equivalent to the integer 0.
Example:
<?php
$x = 0;
switch($x) {
case "a":
   echo "a";
   break;
case "b":
   echo "b";
   break;
default
   echo "default";
}
?>
The result will be an "a" echoed out. What PHP does in this instance, is once it realizes that it's attempting to compare string ("a") to an integer (0), it converts "a" into an integer which ends up satisfying the first case.
The rules for string conversion into integers is available at:
http://us3.php.net/manual/en/language.types.string.php
The easiest way to combat this issue is to force type comparison by using the "===" operator. This makes PHP forego the string to integer conversion.
Example:
<?php
switch(true) {
case $x === "a":
   echo "a";
   break;
case $x === "b":
   echo "b";
   break;
default
   echo "default";
}
?>
Or the switch input can be type-casted to always be a string, etc.
Also note that even though a conditional statement needs to be explicitly set in each case to gain expected behavior, the switch can still execute faster then an "ifelse" block because PHP will not continue to evaluate conditions once a case has been satisfied.


jason

It should be pointed out that this:
<?php
$var = 0;
switch ( $var )
{
case "something":
$foo = "Broken";
break;
default:
$foo = "Okay";
break;
}
echo $foo;
?>
Will print out "Broken".  It's not broken, because in PHP, when an Integer and a String are compared, the string is == 0.  So 0 == "something".  However, this is not apparent.  switch() does not do type checking.


gregory dot mccoy

In the post:
----------------------------------------------------
design at hyperoptix dot com
18-Feb-2004 12:46
Boolean logic does not work inside case statements:
<?php
$x = 18;
$y = 6;
switch ($x) {
  case (($y * 4) || (9 * 3)):
      echo "Member";
      break;
  default:
      echo "Not a member";
}
?>
echoes "Member".
----------------------------------------------------
there were many responses but all seem to miss the point.  You cannot mix apples and oranges.  The "switch($x)" establishes that this "switch" statement will be a Relational syntax while the "case" qualifier uses a Logical syntax.  There must be a match.  Either change "switch($x)" to "switch(true)" or change "case(($y * 4) || (9 * 3)):" to resolve to a value.
The syntax of the original post is like a cop that says, "I want all of your answers to reflect truth.  So, are you eighteen?"  The respondent says, " 4 x 4 or 11 + 5".  Need I say more?


jon

In response to the entry by "kriek at jonkriek dot com", I think you would probably be better of doing this:
<?php
   // ensure $_GET['go'] is set, an integer, and not 0
   // then, set nav number; default to 1
   $nav = ( isset($_GET['go']) && (intval($_GET['go']) == $_GET['go']) && $_GET['go'] ) ?
       intval($_GET['go']) : 1;
   // format navigation string and include
   include(sprintf("Page%02d.php",$nav));    
?>
... as oppposed to the switch setup you recommended, which is limited to the number of cases you specify...


mdirks

In response to scott at firefallpro dot com:
"Also note that even though a conditional statement needs to be explicitly set in each case to gain expected behavior, the switch can still execute faster then an "if/elseif/else" block because PHP will not continue to evaluate conditions once a case has been satisfied."
This is not accurate as far as the documentation would say. PHP does not (or at the very least should not) continue to evaluate other "if/elseif/else" statements () on the same level once a true statement is found. It will (should) "short-circuit" to after the else block in the same depth-level, once it has finished executing all the code in it's block naturally.
Where the switch statement wins out over an "if/elseif/else" block is it's ability to "fall though" to instructions in following cases until a break is encountered. Coding something similiar using "if/elseif/else" statements could get really messy and buggy really fast depending on the switch statement.


juraj5

In response to 'i luv spam',
when you enter 07, you tell PHP to interpret a number as an octal number (much like '0x' for hex numbers). Octal numbering system uses only 8 digits, i.e. 0-7. http://en.wikipedia.org/wiki/Octal
The number 8 does not exist in octal numbering system. The comparison works because the octal numbers 0 to 7 have identical counterparts in decimal system.
So, in order to get a number compared as decimal 8, you would have to enter 010 in the case.
BTW this behavior obviously isn't specific to switch, it's a part of PHP.
(I personally stumbled into this when trying to make my code nicely indented while declaring an array)


2mareks

In reply to earlier comment, "switch"- I found this to be one of the best ways to interpret 'actions'. Simply create a new instance of Handler_action before including any content source files. This is a highly stripped version of the class.
The real one I created handles (and secures) input for $_GET and $_POST, creates a 'permission' array that only allows certain actions to be called by non-admins, and creates handy little diagnostic messages that can be displayed upon redirecting.
On that note, the beauty in this class really shines in the simple redirect. You wont be left with ugly URLs like, "http://www.domain.com/path/to/script.php?action=blah&var1=123". Rather, you will be left with something like "http://www.domain.com/path/to/script.php"- helps protect some of the site by not showing any vulnerabilities in URLs.
Also, this class keeps all actions organized neatly by directly passing $_GET vars to the actions through function parameters.
<?php
 class Handler_action {
   function __construct( ){
     //Add code here to secure attacks through $_GET or use $_POST
     $action = $_GET["action"];
 
     //$actions_index conventions:
     //'action_name' => array( 'arg1', 'arg2', 'etc', ['/redirect/to/path' | NULL ] )
     $actions_index = array(
       'create' => array( $_GET['newVar1'], $_GET['newVar2'], '/home.php' ),
       'edit' => array( $_GET['id'], $_GET['otherVar'], '/home.php' ),
       'delete' => array( $_GET['id'], '/other_script.php' )
     );
 
     if( $action && array_key_exists( $action, $actions_index ) ){
       $redirect_path = array_pop( $actions_index[$action] );
       call_user_func_array( array( &$this, $action ), $actions_index[$action] );
       if( $redirect_path )
         header( "Location: http://www.domain.com{$redirect_path}" );
     }
   }
   //being defining actions now
   function create( $new_var1, $new_var2 ){
 
     //code...
 
   }
   function edit( $id, $other_var ){
 
     //code...
 
   }
   function delete( $id ){
 
     //code...
 
   }
 }
?>


ezekiel

In reply to Alex Fung :
The following code doesn't work :
<?php
$x = 18;
$y = 6;
switch ($x) {
  case (($y * 4) || (9 * 3)):
      echo "Member";
      break;
  default:
      echo "Not a member";
}
?>
Why :
<design at hyperoptix dot com> want to test if $x == $y*4 or $x == 9*3 ($x == (($y*4)||(9*3))
However the case statement evaluate the value of (($y*4)||(9*3)) that is always true because 9*3=27 (!=0)
That's why this code always return true when $x != 0.
The correct code would be :
<?php
$x = 18;
$y = 6;
switch ($x) {
  case (($y * 4)):
  case ((9*3)):
       echo "Member";
       break;
  default:
      echo "Not a member";
}
?>
Boolean logic work inside case statement, you just need to know that the expression in the case statement is first evaluated then compared with the evaluated value in the switch statement.


sneskid

In regard to what dohpaz at kennethpaul dot com wrote.
If you ever have time you may want to test out having a premade associative array with the required elements eaqualing the needed value. Then assign the value based on the array element.
in dohpaz's month example it would look like this:
<?php
$arr_month = array(
'January' => 1,
'February' => 2,
'March' => 3,
'April' => 4,
'May' => 5,
'June' => 6,
'July' => 7,
'August' => 8,
'September' => 9,
'October' => 10,
'November' => 11,
'December' => 12);
foreach($arr_month as $k => $v) {$arr_month[substr($k,0,3)] = $v;} // autogen a 3 letter version
//note that the overall size will be 23 because May will only exist once
$month = 'Jan';
$month = $arr_months[$month];
echo $month; // outputs: 1
?>
It beats a switch in this case.
I did some benchmarking.
The array system is faster than the switch system.
Here were my average time results of 1000 itterations of assigning the numeric value to the month.
The value was randomized between each itteration (this was not added to the benchmark value), so each method was simulated with various data to stress different points.
array:
'avg' => 1.09958648682E-6
switch:
'avg' => 4.32157516479E-6
switch (true):
'avg' => 6.90913200378E-6
Contrary to what dohpaz suggested I found that a normal switch was faster than a switch(true) version.
I repeated these test several times to take into acount server load variations. The ratios were always consistent.
The array way is notably faster.


paz

In case : ) it helps someone, I was able to clean up some hairball code by using nested switches (didn't see it mentioned here).  Thanks to all those who are writing examples - I love this site!
<?php
$string_match="second";
switch ($string_match) {
case "first":
case "second":
case "third":
   print "<H3>Something for all three</H3>
";
   switch ($string_match) {
     case "first":
     print "something for first only";
     break;
     case "second":
     case "third":
     print "something for the other two";
     break;
   }
break;
default:
print "<H3>no match</H3>";
}
?>


rmunn

In answer to njones at fredesign dot com, what you're seeing is the way the switch statement is supposed to work. The switch statement evaluates the cases, top to bottom, until it finds the first one that matches the value being switch()ed on. So, for example, if you had:
<?php
switch(2) {
case 1: echo "One\n"; break;
case 2: echo "Two\n"; break;
case 3: echo "Three\n"; break;
case 2: echo "Two again\n"; break;
}
?>
Only "Two" would get echoed. "Two again" would NOT get echoed, because once the first case matches, the rest of them do NOT get evaluated. As soon as a matching case is found, the statements starting at that case get executed until the first break, then control flows out the bottom of the switch block.


tom

If you're using switch() inside a function and you're returning a $var inside each case, you won't need to include break() as return() will end the execution of the switch and function.

27-oct-2006 11:29

I could have used a swich for this, but I found that using the array was much faster.
   $action = $_GET['action'];
   $pages = array
   (
     'edit'   => './edit.php',
     'search' => './search.php'
   );
   if(strlen($pages[$action]) > 0)
   {
     require $pages[$action];
   }
   else
   {
     require './default.php';
   }


rdoggett

Here's an often overlooked way of doing (nearly) the same thing:
<?php
echo ($i == 0) ?   "i is zero" :
 (($i == 1) ?  "i equals 1" :
 (($i == 2) ?  "i equals 2" : ""));
?>
This may be an idiomatic surprise at first.  But the clean and concise code speaks for itself.
Beware; PHP seems to parse the ternary operator with a different precedence than other languages such as C or perl or javascript.  This means PHP requires nested parenthesis around each nested group to avoid unexpected results.  Even so, this construct is still very understandable and maintainable, compared to the equivalent switch or if statements.


fteng1

Here's a lazy way of doing an comparison where multiple conditions equal the same result using arrays.
if (in_array($year,array(1948, 1960, 1972, 1984, 1996, 2008)))
echo "Rat";
elseif (in_array($year,array(1949, 1961, 1973, 1985, 1997, 2009)))
echo "Ox";
elseif (in_array($year,array(1950, 1962, 1974, 1986, 1998, 2010)))
echo "Tiger";
elseif (in_array($year,array(1951, 1963, 1975, 1987, 1999, 2011)))
echo "Rabbit";
elseif (in_array($year,array(1952, 1964, 1976, 1988, 2000, 2012)))
echo "Dragon";
elseif (in_array($year,array(1941, 1953, 1965, 1977, 1989, 2001)))
echo "Snake";
elseif (in_array($year,array(1942, 1954, 1966, 1978, 1990, 2002)))
echo "Horse";
elseif (in_array($year,array(1943, 1955, 1967, 1979, 1991, 2003)))
echo "Lamb";
elseif (in_array($year,array(1944, 1956, 1968, 1980, 1992, 2004)))
echo "Monkey";
elseif (in_array($year,array(1945, 1957, 1969, 1981, 1993, 2005)))
echo "Rooster";
elseif (in_array($year,array(1946, 1958, 1970, 1982, 1994, 2006)))
echo "Dog";
elseif (in_array($year,array(1947, 1959, 1971, 1983, 1995, 2007)))
echo "Boar";


gmgiles

Did you know that switch() and case() can also accomodate things like basic math calculations and counter incrementing? They do. In this example, I use a switch statement (which is inside of a while loop) to alternate the background color of a table row. It gives me a cool spool-printer-paper effect.
<?php
$rows_per_color = 5;  // change bgcolor every 5 rows
switch($ctr++) {
case 0:
$bgcolor = "#ffffff";
break;
case ($rows_per_color):
$bgcolor = "#ff0000";
break;
case ($rows_per_color * 2):
$bgcolor = "#ffffff";
$ctr = 1;
break;
}
?>
As you can see, I increment $ctr by 1 in the switch() itself, and the final case() does a simple calculation. Simple, but powerful. [Remember, the above example is inside of a while() loop... each time it iterates, switch increments $ctr.]


php dot net dot 1

Declaring a variable (actually an array) as static w/in a switch{} spun my wool for a while:
don't:
<?
function ss() {
   switch ("bug") {
       case "bug" :
          static $test = "xyz";
          break;
       default :
          static $test = "abc";
   }
echo $test;
}
ss(); //abc
?>
do:
<?
function tt() {
   static $test;
   switch ("fix") {
       case "fix" :
          $test = "xyz";
          break;
       default :
          $test = "abc";
   }
echo $test;
}
tt(); // xyz
?>


chernyshevsky

Be very careful when you're using text strings as cases. If the variable supplied to switch() is an integer, the cases would be converted to integer before the comparison is made (usually to zero). The following snippet prints "hello".
<?php
$a = 0;
switch($a) {
case 'Hello': echo "Hello";
break;
}
?>


bachsau

Be carefull: If you want to test the return of a function, you have to use switch, because if you use 'if' and 'ifelse', your function will be executed every time again.
For example if use use the following construct:
if(file_get_contents('file.htm', 0) == 'typ1') {
    // Do one thing
}
ifelse(file_get_contents('file.htm', 0) == 'typ2') {
    // Do the second thing
}
ifelse(file_get_contents('file.htm', 0) == 'typ3') {
    // Do the third thing
}
The file will be requested 3 times!!!
If you use the following:
switch (file_get_contents('file.htm', 0)) {
    case 'typ1': // Do one thing
    break;
    case 'typ2': // Do the second thing
    break;
    case 'typ3': // Do the third thing
}
The file will be requested only once!!!


manicdepressive

Be careful if distinguishing between NULL and (int)0.  As implied in the above documentation, the case statements are equivalent to the '==' operator, not the '===' operator, so the following code did not work as i expected:
<?php
$mixed = 0;
switch($mixed){
  case NULL: echo "NULL";  break;
  case 0: echo "zero";  break;
  default: echo "other"; break;
}
?>
Instead, I may use a chain of else-ifs.  (On this page, kriek at jonkreik dot com states that "in most cases [a switch statement] is 15% faster [than an else-if chain]" but jemore at m6net dotdot fr claims that when using ===, if/elseif/elseif can be 2 times faster than a switch().)
Alternatively, if i prefer the appearance of the switch() statement I may use a trick like the one nospam at please dot com presents:
<?php
$mixed = 0;
switch(TRUE){
  case (NULL===$mixed): //blah break;
  case (0   ===$mixed): //etc. break;
}
?>
code till dawn! mark meves!


bishop

As jason at devnetwork dot net and others have pointed out, using switch() when you wish to compare against strings can be dangerous:
<?php
$bug = 0;
switch ($bug) {
   case 'fly':
       echo 'flies buzz';
       break;
   case 'mantis':
       echo 'mantes pray';
       break;
   default:
       echo 'swat, splat, you are dead';
       break;
}
?>
Will print "flies buzz", NOT "swat, splat, you are dead".
Remember PHP says that 'fly' == 0, or in general string == 0 is true.
Anyway, avoid that with:
<?php
$bug = 0;
switch ($bug === 0 ? '' : $bug) {
   case 'fly':
       echo 'flies buzz';
       break;
   case 'mantis':
       echo 'mantes pray';
       break;
   default:
       echo 'swat, splat, you are dead';
       break;
}
?>
Prints out what you expect:
Swat
Splat
You are dead
P.S.: that's an empty string (single quote single quote), not a spurious double quote.


okke

As a reply to zzo38: please don't -ever- use that code. Labels are generally considered a bad programming practise. If you mis-use switch statements in order to simulate the workings of labels, that's double bad.
Why not use a simple if/then/else statement? It's readable and less prone to bugs.


drake

Also,
when using switch for mode selecting on websites like:
switch($_GET['mode']) {
 case "gallery":
   //code
 break;
 case "news":
   //code
 break;
 case "stuff":
   //code
 break;
 default, etc etc
}
Will NOT trigger the string == 0 bug, because $_GET automatically parse anything passed to them as strings.
(same applies for all browser variables: SESSION, POST etc)
so passing:
mode=0
into the address bar is the same as:
$_GET['mode'] = "0"; //not $_GET['mode'] = 0;
thought it may help.


peterc

Along the lines of using expressions in switch statements.  I came across some code which wrapped switch statements in 'if' blocks like so...
if (isset($var) {
   switch($var) {
       ....
   
But I found the following a little cleaner.
switch ( isset($var) ? $var : defaultValue ) {
...


derek ethier

A word of caution around the order used for the case/default controls.  I notice that a lot of people do not break; the default section and the following could lead to incorrect results when run.
$a = "lowercase";
switch ( $a ) {
 default:
   $a = strtoupper( $a );
   print $a . "<br />";
 case ( 'LOWERCASE' ):
   print $a . "<br />";
   break;
}
Result:
LOWERCASE
LOWERCASE
Placing a break; in the default control will result in:
LOWERCASE
.. as expected.  Also, placing the default section at the bottom (as in an else control) will also display the correct result.


usera$

A note as to how the comparisons of case values to the switch value are being made would be useful, since it appears, the comparison operator === is not available, only ==. That means, according to the example given, in
switch($a)
...
case 0
 statement-0
case FALSE
 statment-1
case NULL
 statement-2
...
both statement-1 and statement-2 cannot be executed, no matter what the value of $a is, including FALSE.


jonybd

/*
Have one value need to deal with currency
- follow as example
*/
while ($row = mysql_fetch_array($v_Result,MYSQL_NUM)) {
$v_BAL = $row[1]/10000;

switch (TRUE){
case ($v_BAL <= 0): //less then 0 , -0
echo $v_BAL;
break;

case ($v_BAL <= 10 AND $v_BAL >= 1): //less then 10 and greater then 1
echo $v_BAL;
break;

default: //default
echo $v_BAL;
break;
}
}


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