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Dodatek O. PHP type comparison tables
The following tables demonstrate behaviors of PHP
types and
comparison
operators, for both loose and strict comparisons. This
supplemental is also related to the manual section on
type juggling.
Inspiration was provided by various user comments and by the work over at
BlueShoes.
Before utilizing these tables, it's important to understand types and their
meanings. For example, "42" is a string
while 42 is an integer. FALSE is a
boolean while "false" is a
string.
Notatka:
HTML Forms do not pass integers, floats, or booleans; they pass strings.
To find out if a string is numeric, you may use
is_numeric().
Notatka:
Simply doing if ($x) while $x is
undefined will generate an error of level E_NOTICE.
Instead, consider using empty() or
isset() and/or initialize your variables.
Tabela O-1. Comparisons of $x with PHP functions
Tabela O-2. Loose comparisons with == | | TRUE | FALSE | 1 | 0 | -1 | "1" | "0" | "-1" | NULL | array() | "php" |
|---|
| TRUE | TRUE | FALSE | TRUE | FALSE | TRUE | TRUE | FALSE | TRUE | FALSE | FALSE | TRUE | | FALSE | FALSE | TRUE | FALSE | TRUE | FALSE | FALSE | TRUE | FALSE | TRUE | TRUE | FALSE | | 1 | TRUE | FALSE | TRUE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | | 0 | FALSE | TRUE | FALSE | TRUE | FALSE | FALSE | TRUE | FALSE | TRUE | FALSE | TRUE | | -1 | TRUE | FALSE | FALSE | FALSE | TRUE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | | "1" | TRUE | FALSE | TRUE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | | "0" | FALSE | TRUE | FALSE | TRUE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | | "-1" | TRUE | FALSE | FALSE | FALSE | TRUE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | | NULL | FALSE | TRUE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | TRUE | TRUE | FALSE | | array() | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | TRUE | TRUE | FALSE | | "php" | TRUE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | TRUE |
Tabela O-3. Strict comparisons with === | | TRUE | FALSE | 1 | 0 | -1 | "1" | "0" | "-1" | NULL | array() | "php" |
|---|
| TRUE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | | 1 | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | | 0 | FALSE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | | -1 | FALSE | FALSE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | | "1" | FALSE | FALSE | FALSE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | | "0" | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | | "-1" | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | | NULL | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | TRUE | FALSE | FALSE | | array() | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | TRUE | FALSE | | "php" | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | TRUE |
PHP 3.0 note:
The string value "0" was considered non-empty in
PHP 3, this behavior changed in PHP 4 where it's now seen as empty.
User Contributed NotesJan
29-Dec-2005 08:23
Note that php comparison is not transitive:
"php" == 0 => true
0 == null => true
null == "php" => false
php [at] barryhunter [.] co [.] uk
07-Sep-2005 09:44
jerryschwartz at comfortable dot com
26-Jul-2005 10:04
In some languages, a boolean is promoted to an integer (with a value of 1 or -1, typically) if used in an expression with an integer. I found that PHP has it both ways:
If you add a boolean with a value of true to an integer with a value of 3, the result will be 4 (because the boolean is cast as an integer).
On the other hand, if you test a boolean with a value of true for equality with an integer with a value of three, the result will be true (because the integer is cast as a boolean).
Surprisingly, at first glance, if you use either < or > as the comparison operator the result is always false (again, because the integer as cast as a boolean, and true is neither greater nor less than true).
tom
17-Jun-2005 11:27
<?php
if (strlen($_POST['var']) > 0) {
}
?>
When working with HTML forms this a good way to:
(A) let "0" post values through like select or radio values that correspond to array keys or checkbox booleans that would return FALSE with empty(), and;
(B) screen out $x = "" values, that would return TRUE with isset()!
Because HTML forms post values as strings, this is a good way to test variables!
[[Editor Note: This will create a PHP Error of level E_NOTICE if the checked variable (in this case $_POST['var']) is undefined. It may be used after (in conjuection with) isset() to prevent this.]]
aidan at php dot net
24-Jan-2005 04:00
The way PHP handles comparisons when multiple types are concerned is quite confusing.
For example:
"php" == 0
This is true, because the string is casted interally to an integer. Any string (that does not start with a number), when casted to an integer, will be 0.
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