PHP equality comparison and empty, isset, isnull

Variable is empty

The following are considered empty:

• "" (empty string)
• 0 (0 as an integer)
• 0.0 (0 as a floating point number)
• "0 ” (0 as a string)
• NULL
• FALSE
• array() (an empty array)
• $var; (a variable declared but without a value)

The null value in the judgment statement returns false , the following code will not produce any output, because the judgments in the if statement are all false:

<code><span>$emptyList</span> = [<span>""</span>,  <span>0</span>, <span>0.0</span>, <span>"0"</span>, <span>NULL</span>, <span>FALSE</span>, <span>array</span>(), <span>$var</span>, ];
<span>foreach</span>(<span>$emptyList</span><span>as</span><span>$val</span>) {
    <span>if</span> (<span>$val</span>) {
        var_dump(<span>$val</span>);
    }
}</code>

Comparison operators: == and ===

• == only involve the comparison of values ​​

<code>var_dump(<span>0</span> == <span>'0.0'</span>); <span>//</span><span>true</span>
var_dump(<span>0</span> == <span>''</span>); <span>//</span><span>true</span>
var_dump(<span>0</span> == <span>false</span>); <span>//</span><span>true</span></code>

• === It also involves the comparison of values ​​and types, which is more strict.

<code>var_dump(<span>0</span> === <span>'0.0'</span>); <span>//</span><span>false</span>
var_dump(<span>0</span> === <span>''</span>); <span>//</span><span>false</span>
var_dump(<span>0</span> === <span>false</span>); <span>//</span><span>false</span></code>

• null is compared with the null value through ==. Except for "0", all return true:

<code><span><span><?php</span><span>$emptyList</span> = [<span>""</span>,  <span>0</span>, <span>0.0</span>, <span>"0"</span>, <span>NULL</span>, <span>FALSE</span>, <span>array</span>(), <span>$var</span>, ];
<span>foreach</span>(<span>$emptyList</span><span>as</span><span>$val</span>) {
    var_dump(<span>$val</span> == <span>null</span>);
}</span></code>

empty , isset, isnull

• empty: Check whether a variable is empty

<code><?php
<span>$emptyList</span> = [<span>""</span>,  <span>0</span>, <span>0.0</span>, <span>"0"</span>, NULL, FALSE, array(), <span>$var</span>, ];
foreach (<span>$emptyList</span> as <span>$e</span>) {
    var_dump(empty(<span>$e</span>));
}
/*
bool(<span>true</span>)
bool(<span>true</span>)
bool(<span>true</span>)
bool(<span>true</span>)
bool(<span>true</span>)
bool(<span>true</span>)
bool(<span>true</span>)
bool(<span>true</span>)
*/</code>

• isset: Return TRUE if the variable var exists and the value is not NULL, otherwise return FALSE.

<code><span>$var</span> = <span>1</span>;
var_dump(<span>isset</span>(<span>$var</span>)); <span>// true</span><span>unset</span>(<span>$var</span>);
var_dump(<span>isset</span>(<span>$var</span>)); <span>// false</span><span>$var</span> = <span>null</span>;
var_dump(<span>isset</span>(<span>$var</span>)); <span>// false</span></code>

• isnull: Determine whether the variable is null, equivalent to === null.

Note that the

==

comparison between null values ​​may not necessarily return true:

<code><span>// 不具传递性</span><span>var_dump(<span>0</span> == <span>'0'</span>)</span>; <span>// true</span><span>var_dump(<span>''</span> == <span>0</span> )</span>; <span>// true</span><span>var_dump(<span>'0'</span> == <span>''</span>)</span>; <span>// false</span><span>var_dump(<span>0</span> == [])</span>; <span>// false</span></code>

Best practice

• Use empty to judge null values;
• isset cannot judge variables that exist but have a null value; The difference between
• php == and === is that the latter performs type equality judgment at the same time

').addClass('pre-numbering').hide(); $(this).addClass('has-numbering').parent().append($numbering); for (i = 1; i ').text(i)); }; $numbering.fadeIn(1700); }); });

The above introduces PHP equality comparison and empty, isset, isnull, including the content. I hope it will be helpful to friends who are interested in PHP tutorials.