Detailed interpretation of PHP comparison operators

Detailed interpretation of PHP comparison operators_PHP tutorial

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Release： 2016-07-15 13:33:33

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Table 1. PHP comparison operators

Example name result
$a == $b equals TRUE if $a equals $b.
$a === $b is congruent 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 Congruent TRUE if $a is not equal to $b, or their types are different. (PHP 4 only)
$a < $b is less than TRUE if $a is strictly less than $b.
$a > $b is greater than TRUE if $a is strictly $b.
$a <= $b is less than or equal to TRUE if $a is less than or equal to $b.
$a >= $b is greater than or equal to TRUE if $a is greater than or equal to $b.

If the PHP comparison operator compares an integer and a string, the string will be converted to an integer. If comparing two numeric strings, compare as integers. This rule also applies to switch statements.

<ol class="dp-xml"><li class="alt"><span><span class="tag"><</SPAN><SPAN> ?php  </SPAN></SPAN><LI><SPAN>var_dump(</SPAN><SPAN class=attribute>0</SPAN><SPAN> == "a"); // </SPAN><SPAN class=attribute>0</SPAN><SPAN> == 0 -</SPAN><SPAN class=tag>></span><span> true  </span><li class="alt">
<span>var_dump("1" == "01"); // </span><span class="attribute">1</span><span> == 1 -</span><span class="tag">></span><span> true  </span>
</li>
<li><span>switch ("a") {  </span></li>
<li class="alt"><span>case 0:  </span></li>
<li><span>echo "0";  </span></li>
<li class="alt"><span>break;  </span></li>
<li><span>case "a": // never reached because "a" is already matched with 0  </span></li>
<li class="alt"><span>echo "a";  </span></li>
<li><span>break;  </span></li>
<li class="alt"><span>}  </span></li>
<li>
<span class="tag">?></span><span>  </span>
</li></span></li></ol>

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If the operands are of different types, they are compared (in order) according to the following table.

Table 2. PHP comparison operators compare different types

Operator 1 Type Operand 1 Type result
null or string string Convert NULL to "" , perform numerical or lexical comparison
bool or null Any other type is converted to bool, FALSE < TRUE
object object Built-in classes can define their own comparisons, different classes cannot be compared, and attributes of the same class and arrays are compared in the same way ( PHP 4), PHP 5 has its own instructions

string, resource or number string, resource or number Convert strings and resources to numbers, compared by normal math
array array has fewer members The array is smaller. If the key in operand 1 does not exist in operand 2, the array cannot be compared, otherwise the values are compared one by one (see the example below)

array Any other type of array is always larger
object Any other type of object is always larger

Example 1. Standard array comparison code

<OL class=dp-xml><LI class=alt><SPAN><SPAN class=tag><</SPAN><SPAN> ?php  </SPAN></SPAN><LI><SPAN>// 数组是用标准比较运算符这样比较的  </SPAN><LI class=alt><SPAN>function standard_array_compare($op1, $op2)  </SPAN><LI><SPAN>{  </SPAN><LI class=alt><SPAN>if (count($op1) </SPAN><SPAN class=tag><</SPAN><SPAN> </SPAN><SPAN class=tag-name>count</SPAN><SPAN>($op2)) {  </SPAN><LI><SPAN>return -1; // $op1 </SPAN><SPAN class=tag><</SPAN><SPAN> $op2  </SPAN><LI class=alt><SPAN>} elseif (count($op1) </SPAN><SPAN class=tag>><span> count($op2)) {  </span></p>
<li>
<span>return 1; // $op1 </span><span class="tag">></span><span> $op2  </span>
</li>
<li class="alt"><span>}  </span></li>
<li>
<span>foreach ($op1 as $</span><span class="attribute">key</span><span> =</span><span class="tag">></span><span> $val) {  </span>
</li>
<li class="alt"><span>if (!array_key_exists($key, $op2)) {  </span></li>
<li><span>return null; // uncomparable  </span></li>
<li class="alt">
<span>} elseif ($val </span><span class="tag"><</SPAN><SPAN> $op2[$key]) {  </SPAN><LI><SPAN>return -1;  </SPAN><LI class=alt><SPAN>} elseif ($val </SPAN><SPAN class=tag>></span><span> $op2[$key]) {  </span>
</li>
<li><span>return 1;  </span></li>
<li class="alt"><span>}  </span></li>
<li><span>}  </span></li>
<li class="alt">
<span>return 0; // $</span><span class="attribute">op1</span><span> == $op2  </span>
</li>
<li><span>}  </span></li>
<li class="alt">
<span class="tag">?></span><span> </span>
</li>
<p><strong>PHP comparison operator ternary operator </strong></p>
<p>Another conditional operator is the "?:" (or ternary) operator. Example 2. Assign default value </p>
<pre class="brush:php;toolbar:false"><ol class="dp-xml"><li class="alt"><span><span class="tag"><</SPAN><SPAN> ?php  </SPAN></SPAN><LI><SPAN>// Example usage for: Ternary Operator  </SPAN><LI class=alt><SPAN>$</SPAN><SPAN class=attribute>action</SPAN><SPAN> = (empty($_POST['action'])) <br>? 'default' : $_POST['action'];  </SPAN><LI><SPAN>// The above is identical to <br>this if/else statement  </SPAN><LI class=alt><SPAN>if (empty($_POST['action'])) {  </SPAN><LI><SPAN>$</SPAN><SPAN class=attribute>action</SPAN><SPAN> = </SPAN><SPAN class=attribute-value>'default'</SPAN><SPAN>;  </SPAN><LI class=alt><SPAN>} else {  </SPAN><LI><SPAN>$</SPAN><SPAN class=attribute>action</SPAN><SPAN> = $_POST['action'];  </SPAN><LI class=alt><SPAN>}  </SPAN><LI><SPAN class=tag>?></span><span>   </span></span></li></ol>

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Expression (expr1) ? (expr2) : (expr3) When expr1 evaluates to TRUE, the value is expr2, and when expr1 evaluates to FALSE, the value is expr3.

Note: Note that the ternary operator is a statement, so its evaluation is not a variable, but the result of the statement. This is important if you want to return a variable by reference. The statement return $var == 42 ? $a : $b; in a function that returns by reference will not work, and a future version of PHP will issue a warning about this.