PHP 比較操作符

Comparison Operators

Example	Name	Result
$a == $b	Equal	TRUE if $a is equal to $b.
$a === $b	Identical	TRUE if $a is equal to $b, and they are of the same type. (introduced in PHP 4)
$a != $b	Not equal	TRUE if $a is not equal to $b.
$a <> $b	Not equal	TRUE if $a is not equal to $b.
$a !== $b	Not identical	TRUE if $a is not equal to $b, or they are not of the same type. (introduced in PHP 4)
$a < $b	Less than	TRUE if $a is strictly less than $b.
$a > $b	Greater than	TRUE if $a is strictly greater than $b.
$a <= $b	Less than or equal to	TRUE if $a is less than or equal to $b.
$a >= $b	Greater than or equal to	TRUE if $a is greater than or equal to $b.

 

注意：如果將字串和一個integer類型的值比較。string會轉化為number類型（integer類型或者float類型），然後再和integer進行比較。

 

 1 <?php
 2  var_dump(0 == "a"); // 0 == 0 -> true
 3  var_dump("1" == "01"); // 1 == 1 -> true
 4 var_dump("1" == "1e0"); // 1 == 1 -> true
 5 
 6 switch ("a") {
 7 case 0:
 8     echo "0";
 9     break;
10 case "a": // never reached because "a" is already matched with 0
11     echo "a";
12     break;
13 }
14 ?> 
15 

 

 

Comparison with Various Types

Type of Operand 1	Type of Operand 2	Result
null or string	string	Convert NULL to "", numerical or lexical comparison
bool or null	anything	Convert to bool, FALSE < TRUE
object	object	Built-in classes can define its own comparison, different classes are uncomparable, same class - compare properties the same way as arrays (PHP 4), PHP 5 has its own explanation
string, resource or number	string, resource or number	Translate strings and resources to numbers, usual math
array	array	Array with fewer members is smaller, if key from operand 1 is not found in operand 2 then arrays are uncomparable, otherwise - compare value by value (see following example)
array	anything	array is always greater
object	anything	object is always greater

 

在進行比較兩個數的時候，最好先把這個表中的意思全部理解了。才好。

我曾經就在這個吃過虧。

 

還有就是，在比較兩個value的時候，如果能使用 “===”和“！==”操作符的時候就使用這兩個操作符。 以免php自作聰明的進行自動類型轉換。