PHP 比较操作符

**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：如果将字符串和一个integer类型的值比较。string会转化为number类型（integer类型或者float类型），然后再和integer进行比较。

 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

在进行比较两个数的时候，最好先把这个表中的意思全部理解了。才好。

我曾经就在这个吃过亏。

还有就是，在比较两个value的时候，如果能使用 “===”和“！==”操作符的时候就使用这两个操作符。以免php自作聪明的进行自动类型转换。