Detailed explanation of php comparison operators

The

operator is a symbol that tells the compiler to perform specific arithmetic or logical operations. It usually forms an expression together with the operands. We often see it participating in mathematical operations or logical operations. PHP also contains many operators. This article explains in detail the very important Comparison Operator.

Types of Comparison Operators

As their names imply, allow comparison of two values. The comparison operators are as follows:
1) $a > $b is greater than: if $a is strictly greater than $b, then TRUE is returned
2) $a < $b is less than: if $a is strictly less than $b, then return TRUE
3) $a >= $b greater than or equal to: if $a is greater than or equal to $b, then return TRUE
4) $a <= $b less than or equal to: if $a Less than or equal to $b, then return TRUE
5) $a <> $b is not equal to: If $a is not equal to $b, then return TRUE
6) $a != $b is not equal to: if If $a is not equal to $b, then TRUE is returned (same as above)
7) $a == $b is equal to: If $a is equal to $b, then TRUE is returned
8) $a === $b is equal to : If $a is equal to $b, and their types are also the same, return TRUE
9) $a !== $b is not equal to: If $a is not equal to $b, or their types are different, return TRUE

Among them, we need to focus on distinguishing between "equal to" and "equal to". $a == $b only performs a comparison operation on the values ​​​​of two variables, while "equal to" requires the expression of both sides of the operator. The formula compares values ​​and data types at the same time. Only when the values ​​on both sides are equal, the operation result is "true". Combined with the "inequality" operator, for example, $a = 2; var_dump($a!==2); this expression returns "false" because 2 is equal to 2. In addition, $a = 2; is an integer type and 2 in var_dump($a!==2); is also an integer type, but the operator is not exactly equal to "!==", so the result is false, because 2 is equal to 2 . On the other hand, if this is the case $a = 2; var_dump($a!=='2'); the result of the operation is "true", because 2 is not equal to '2', and the following '2' is a string 's '2' means that not all equals not only compare the variable values, but also compare the data types of the variables.

Comparing results of different types in PHP

If PHP comparison operator compares an integer and a string, the string will be converted to Compare after integers. If you compare two numeric strings, they are compared as integers, and this rule also applies to switch statements.
For example:
var_dump(0 == "a"); // Returns TRUE, "a" is converted to 0
var_dump("1" == "01"); // Returns TRUE, Treat as an integer

Comparison between string or null and string: Convert NULL to "" to compare numbers or strings
Comparison between bool or null: Convert to bool, FALSE < TRUE
Object built-in classes can define their own comparisons. Different classes cannot be compared, and properties of the same class are compared
Comparison between strings, resources or numbers: Convert strings and resources into numbers, and compare them according to ordinary mathematics
array Comparison between: Arrays with fewer members are smaller. If the key in operand 1 does not exist in operand 2, the arrays cannot be compared and need to be compared value by value (see the following code)
array and any other type Comparison: array is always larger
Comparison between object and any other type: object is always larger

Array comparison code:

 function standard_array_compare($op1, $op2) 
 { 
   if (count($op1) < count($op2)) {    //具有较少成员的数组较小
     return -1;    // $op1 < $op2 
   } elseif (count($op1) > count($op2)) { 
     return 1;    // $op1 > $op2 
    }  

   foreach ($op1 as $key => $val) { 
    if (!array_key_exists($key, $op2)) { 
       return null;    
    } else if ($val < $op2[$key]) { 
       return -1; 
     } elseif ($val > $op2[$key]) { 
       return 1; 
      } 
   } 
   return 0;   // $op1 == $op2 
 }

Comparison operation The ternary operation symbol in the symbol:

expression (expr1) ? (expr2) : (expr3) When the value of expression expr1 is TRUE, the value is expr2, The value of expression expr1 when it evaluates to FALSE is expr3.

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