5.4. Creating a Dynamic Variable Name
Problem
You want to construct a variable’s name dynamically. For example, you want to use variable names that match the field names from a database query.
Solution
Use PHP’s variable variable syntax by prepending a
$
to a variable whose value is the variable name
you want:
$animal = 'turtles';
$turtles = 103;
print $$animal;
103
Discussion
The previous example prints 103
. Because
$animal
=
'turtles',
$$animal
is
$turtles
, which equals 103.
Using curly braces, you can construct more complicated expressions that indicate variable names:
$stooges = array('Moe','Larry','Curly'); $stooge_moe = 'Moses Horwitz'; $stooge_larry = 'Louis Feinberg'; $stooge_curly = 'Jerome Horwitz'; foreach ($stooges as $s) { print "$s's real name was ${'stooge_'.strtolower($s)}.\n"; } Moe's real name was Moses Horwitz. Larry's real name was Louis Feinberg. Curly's real name was Jerome Horwitz.
PHP evaluates the expression between the curly braces and uses it as
a variable name. That expression can even have function calls in it,
such as strtolower( )
.
Variable
variables are also useful when iterating through similarly named
variables. Say you are querying a database table that has fields
named title_1
, title_2
, etc. If
you want to check if a title matches any of those values, the easiest
way is to loop through them like this:
for ($i = 1; $i <= $n; $i++) { $t = "title_$i"; if ($title == $$t) { /* match */ } }
Of course, it would be more straightforward to store these values ...
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