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English
The is_bool function is used to check whether a variable is a boolean value. Boolean values typically have two states: true or false, which are used in PHP for logical operations and conditional statements. The return value of is_bool is a boolean; it returns true if the variable's type is boolean, otherwise it returns false.
Example code:
<span><span><span class="hljs-variable">$var1</span></span><span> = </span><span><span class="hljs-literal">true</span></span><span>;
</span><span><span class="hljs-variable">$var2</span></span><span> = </span><span><span class="hljs-number">0</span></span><span>;
</span><span><span class="hljs-variable">$var3</span></span><span> = </span><span><span class="hljs-string">"true"</span></span><span>;
<p></span>echo is_bool($var1); // Output: 1 (true)<br>
echo is_bool($var2); // Output: empty (false)<br>
echo is_bool($var3); // Output: empty (false)<br>
</span>In the code above, $var1 is a boolean type, so is_bool($var1) returns true. However, $var2 is an integer type, so is_bool($var2) returns false, even though its value is 0 (in PHP, false can sometimes be represented as 0). Similarly, $var3 is a string type containing the string "true", but is_bool($var3) still returns false because its type is not boolean.
The is_null function is used to check whether a variable is null. null is a special type that indicates a variable has no value. It differs from false, 0, or an empty string. Therefore, is_null returns true only when the variable's value is null, otherwise it returns false.
Example code:
<span><span><span class="hljs-variable">$var1</span></span><span> = </span><span><span class="hljs-literal">null</span></span><span>;
</span><span><span class="hljs-variable">$var2</span></span><span> = </span><span><span class="hljs-number">0</span></span><span>;
</span><span><span class="hljs-variable">$var3</span></span><span> = </span><span><span class="hljs-string">""</span></span><span>;
<p></span>echo is_null($var1); // Output: 1 (true)<br>
echo is_null($var2); // Output: empty (false)<br>
echo is_null($var3); // Output: empty (false)<br>
</span>In the code above, $var1 is null, so is_null($var1) returns true. $var2 is the integer 0, so is_null($var2) returns false, even though 0 often evaluates to false in logical expressions. Similarly, an empty string "" is not considered null, so is_null($var3) returns false.
By comparing the usage of is_bool and is_null, we can observe some key differences in their return behaviors.
Different return types:
The return value of is_bool is always a boolean — either true or false. Even if the checked variable is not boolean, it returns false. is_null also returns a boolean, but it only returns true if the variable is null; otherwise, it returns false.
Different types being checked:
is_bool checks if the variable's type is boolean, while is_null checks if the variable's value is null. This means is_bool focuses solely on whether the variable is boolean, regardless of its specific content; is_null only cares if the variable’s value is null, regardless of its type (boolean or otherwise).
Semantic differences:
is_bool focuses on the logical boolean values (true or false), while is_null focuses on whether a variable is "empty" (i.e., has no value). Although both functions are used to determine variable states, their criteria differ.
PHP, as a loosely typed language, allows different types of values to be converted between each other. Although 0 and false can be interchangeable in many contexts, in PHP, false is a special boolean value, whereas null represents a variable that is undefined or has no value.
is_bool is specifically designed to determine whether a value is a boolean, and booleans have unique semantics in PHP.
is_null is intended to check if a variable is null, regardless of whether the value is boolean or another type.
This design difference allows developers to precisely control variable type checks, avoiding errors or confusion caused by PHP's loose typing.
is_bool checks if a variable is of boolean type, returning only true or false.
is_null checks if a variable is null, also returning only true or false.
The difference in their return behaviors mainly comes from the different subjects and types they check: is_bool focuses on whether a variable is boolean, while is_null focuses on whether it is null.
Understanding these differences helps better grasp PHP’s type system and assists developers in writing more precise code.
