這是本comparsion操作

Question

哪一項是正確的語法正確的語法不等於操作

本 - > =

if($ses_startdate != $startdate) { 
       echo "I am true"; 
      } 

或本！ - > ==

if($ses_startdate !== $startdate) { 
       echo "I am true"; 
      } 

我一直在使用！==早些時候，它的工作沒有任何問題，但不是它創造了一些條件的問題，當我改變它！=它工作正常..爲什麼？

Answer 1

!==比!=更嚴格，!==也檢查數據類型。 例子：

$a = 1; 
$b = '1'; 
$c = 1; 
$d = TRUE; 
// These are true: 
$a == $c; 
$a == $b; 
$a === $c 
$a == $d; 
// but these are FALSE: 
$a === $b; 
$a === $d; 

Answer 2

$a = ''; 
$b = false; 

if($a != $b) 
    //it is not executed since $a and $b are the same (empty) but have different types. 

if($a !== $b) 
    //it is executed, because $a is a string and $b is boolean, even though both of them represent the same value (empty). 

因此，第三=告訴PHP來檢查類型了。

Answer 3

$ses_startdate != $startdate

在做這fork了你的代碼進行任何比較，習慣做的

var_dump ($ses_startdate);

var_dump ($startdate);

只是在此之前，條件等同，自卸值設置到頁面或將其放入您的error_logs中，以便您可以看到PHP在評估變量的類型和值。