PHP does not require (or support) explicit type definition in
variable declaration; a variable's type is determined by the
context in which that variable is used. That is to say, if you
assign a string value to variable $var,
$var becomes a string. If you then assign an
integer value to $var, it becomes an
integer.
An example of PHP's automatic type conversion is the addition
operator '+'. If any of the operands is a float, then all
operands are evaluated as floats, and the result will be a
float. Otherwise, the operands will be interpreted as integers,
and the result will also be an integer. Note that this does NOT
change the types of the operands themselves; the only change is in
how the operands are evaluated.
If the last two examples above seem odd, see String
conversion to numbers.
If you wish to force a variable to be evaluated as a certain type,
see the section on Type
casting. If you wish to change the type of a variable, see
settype().
If you would like to test any of the examples in this section, you
can use the var_dump() function.
Note:
The behaviour of an automatic conversion to array is currently
undefined.
Since PHP (for historical reasons) supports indexing into strings
via offsets using the same syntax as array indexing, the example
above leads to a problem: should $a become an array with its first
element being "f", or should "f" become the first character of the
string $a?
The current versions of PHP interpret the second assignment as
a string offset identification, so $a becomes "f", the result
of this automatic conversion however should be considered
undefined. PHP 4 introduced the new curly bracket syntax to access
characters in string, use this syntax instead of the one presented
above:
See the section titled String
access by character for more information.
Type casting in PHP works much as it does in C: the name of the
desired type is written in parentheses before the variable which
is to be cast.
The casts allowed are:
(int), (integer) - cast to integer
(bool), (boolean) - cast to boolean
(float), (double), (real) - cast to float
(string) - cast to string
(array) - cast to array
(object) - cast to object
Note that tabs and spaces are allowed inside the parentheses, so
the following are functionally equivalent:
Note:
Instead of casting a variable to string, you can also enclose
the variable in double quotes.
It may not be obvious exactly what will happen when casting
between certain types. For more info, see these sections:
