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 comparison.
In the following example, each code block is equivalent.
One uses a series of if
and
elseif
statements, and the other a
switch
statement. In each case, the output is the same.
Example #1 switch
structure
<?php
// This switch statement:
switch ($i) {
case 0:
echo "i equals 0";
break;
case 1:
echo "i equals 1";
break;
case 2:
echo "i equals 2";
break;
}
// Is equivalent to:
if ($i == 0) {
echo "i equals 0";
} elseif ($i == 1) {
echo "i equals 1";
} elseif ($i == 2) {
echo "i equals 2";
}
?>
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
whose expression evaluates to 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:
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.
A special case is the default
case. This case matches
anything that wasn't matched by the other cases. For example:
Note:
Multiple default cases will raise a
E_COMPILE_ERROR
error.
Note:
Technically the default
case may be listed
in any order. It will only be used if no other case matches.
However, by convention it is best to place it at the end as the
last branch.
If no case
branch matches, and there is no default
branch, then no code will be executed, just as if no if
statement was true.
A case value may be given as an expression. However, that expression will be
evaluated on its own and then loosely compared with the switch value. That means
it cannot be used for complex evaluations of the switch value. For example:
For more complex comparisons, the value true
may be used as the switch value.
Or, alternatively, if
-else
blocks instead of switch
.
The alternative syntax for control structures is supported with
switches. For more information, see Alternative syntax
for control structures.
It's possible to use a semicolon instead of a colon after a case like: