What do three equal signs mean in php

In PHP, the three equal signs "===" are congruent comparison operators, used to compare whether the values ​​of two operands are equal; this operator is used to compare given variables or values. A strict comparison that compares and sees if two variables (expressions or constants) are equal in value and have the same data type, i.e. both are strings or both are integers, etc. This operator returns true if two variables (expressions or constants) contain the same value and the same data type, otherwise it returns false.

The operating environment of this tutorial: windows7 system, PHP8 version, DELL G3 computer

In php, three equal signs " ===" is the congruence comparison operator, also known as the identity operator.

Operator	Name	Description
===	Congruence	Compares whether the values ​​of the two operands are equal and checks whether their types are the same

Identity (=== ) operator is a strict comparison between given variables or values; it compares not only the values ​​of the expressions on both sides of the operator, but also the data types, only the values ​​and data on both sides When the types are equal, the operation result is TRUE.

• This operator returns true if two variables (expressions or constants) contain the same value and the same data type, otherwise it returns false.

<?php 
header("content-type:text/html;charset=utf-8");  
// 给变量赋整数值
$x = 999; 
echo &#39;$x=&#39;.$x."<br>"; 
// 给变量赋字符串值
$y = &#39;999&#39;; 
echo &#39;$y=&#39;.$y."<br>"; 
//比较$x 和$y 
if ($x === $y) 
    echo &#39;$x和$y相等&#39;; 
else
    echo &#39;$x和$y不相等&#39;; 
?>

Explanation: In the above example, the values ​​of $x and $y are equal but the data types are different, so false is returned and the else part is executed. .

Comparison: Equality (==) Operator

The Equality (==) operator compares and tests the variable (expression or constant) on the left Has the same value as the variable (expression or constant) on the right; the comparison performed by this operator is loose.

If the two values ​​​​are the same (it only compares the value of the variable, not the data type), it returns a true value; if the two values ​​​​are not the same, it returns a false value.

Note: The equality (==) operator and the assignment (=) operator are different. The assignment (=) operator changes the variable on the left, assigning the variable on the right to the variable on the left, while the equality (==) operator tests for equality and returns true or false depending on the comparison.

<?php 
header("content-type:text/html;charset=utf-8");  
// 给变量赋整数值
$x = 999; 
echo &#39;$x=&#39;.$x."<br>"; 
// 给变量赋字符串值
$y = &#39;999&#39;; 
echo &#39;$y=&#39;.$y."<br>"; 
//比较$x 和$y 
if ($x == $y) 
    echo &#39;$x和$y的值相等&#39;; 
else
    echo &#39;$x和$y的值不相等&#39;; 
?>

Note: In the above example, because the equality (==) operator only compares the values ​​of variables, the values ​​of $x and $y are equal, Therefore, the statement in the if is executed directly, and the else statement is not executed.

Extended information: PHP comparison operators

##$a != $b is not equal to If the value of $a is not equal to $b after type conversion value, returns TRUE, otherwise returns FALSE$a $b is not equal to is the same as !=, if the type conversion If the value of $a is not equal to the value of $b, TRUE is returned, otherwise FALSE is returned $a !== $bNot equalIf the value of $a is not equal to the value of $b, or the types of their values ​​are different, return TRUE, otherwise return FALSE$a Small andIf the value of $a is less than the value of $b, it returns TRUE, otherwise it returns FALSE$a > $b is greater than If the value of $a is greater than the value of $b, return TRUE, otherwise return FALSE$a Less than or equal to If the value of $a is less than or equal to the value of $b, return TRUE, otherwise return FALSE$a >= $b Greater than or equal toIf the value of $a is greater than or equal to the value of $b, return TRUE, otherwise return FALSE##$a $b$a ?? $b ?? $c Recommended study: "

Example	Name	Description
$a == $b	Equal to	If the values ​​of $a and $b are equal after type conversion, TRUE is returned, otherwise FALSE
$a === $b	Congruent	If $a and $b are not only equal in value, but also have equal types of their values, then Return TRUE, otherwise return FALSE
Spaceship operator (combined comparison operator)	When $a is less than, equal to, or greater than $b, return an integer value less than, equal to, or greater than 0 respectively. PHP7 starts to provide.
NULL merge operator	The first one exists from left to right And the operand is not NULL. If neither is defined and is not NULL, NULL is returned. Available starting with PHP7.

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