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# 附錄 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.

> 備注: 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().

> 備注: 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.

表格 O-1.Comparisons of $x with PHP functions

Expression | gettype() | empty() | is_null() | isset() | boolean : if($x)
--- | --- | --- | --- | --- | ---
$x = ""; | string | `TRUE` | `FALSE` | `TRUE` | `FALSE`
$x = `NULL` | NULL | `TRUE` | `TRUE` | `FALSE` | `FALSE`
var $x; | NULL | `TRUE` | `TRUE` | `FALSE` | `FALSE`
$x is undefined | NULL | `TRUE` | `TRUE` | `FALSE` | `FALSE`
$x = array(); | array | `TRUE` | `FALSE` | `TRUE` | `FALSE`
$x = false; | boolean | `TRUE` | `FALSE` | `TRUE` | `FALSE`
$x = true; | boolean | `FALSE` | `FALSE` | `TRUE` | `TRUE`
$x = 1; | integer | `FALSE` | `FALSE` | `TRUE` | `TRUE`
$x = 42; | integer | `FALSE` | `FALSE` | `TRUE` | `TRUE`
$x = 0; | integer | `TRUE` | `FALSE` | `TRUE` | `FALSE`
$x = -1; | integer | `FALSE` | `FALSE` | `TRUE` | `TRUE`
$x = "1"; | string | `FALSE` | `FALSE` | `TRUE` | `TRUE`
$x = "0"; | string | `TRUE` | `FALSE` | `TRUE` | `FALSE`
$x = "-1"; | string | `FALSE` | `FALSE` | `TRUE` | `TRUE`
$x = "php"; | string | `FALSE` | `FALSE` | `TRUE` | `TRUE`
$x = "true"; | string | `FALSE` | `FALSE` | `TRUE` | `TRUE`
$x = "false"; | string | `FALSE` | `FALSE` | `TRUE` | `TRUE`

表格 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`

表格 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.

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