Summary of usage of PHP isset(), is_null, empty()

These variable judgment functions are actually used quite a lot in PHP development, and they all look similar at first glance, but in fact there are still many differences. If you are not sure, , maybe there will be some potential bugs left, including the fact that I have encountered such pitfalls myself. For example, once I encountered a problem with using empty to judge. The front end allows input of 0, but if I use empty to judge, it will not work. If it is true, I will report the error directly, so this judgment cannot be used here.

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Let’s first look at the specific uses of these functions

isset — Detection Whether the variable has been set and non-NULL

empty - Check whether a variable is empty, the following things 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)

is_null — Detect variables Whether it is NULL

一isset

Determine whether the variable has been defined first, whether the key value of the array exists, etc.

<?php
$data=[""," ", 0, 0.0 ,"0", null, "null", true, false ,[]];
foreach ($data as $key => $val){
    echo $key . &#39;=>&#39; . var_dump(isset($val)) . "\r\n";
}
//以上输出只有 null返回false,其它都为真
$arr = [&#39;name&#39; =>&#39;lc&#39;, &#39;age&#39; => 22, &#39;address&#39; =>null];
echo isset($arr[&#39;name&#39;]) . "\r\n";  //true
echo isset($arr[&#39;mobile&#39;])."\r\n";  //false
echo isset($arr[&#39;address&#39;]) ."\r\n"; //false
//未定义的键和值为null,返回false

empty

$data=[""," ", 0, 0.0 ,"0", null, "null", true, false ,[]];
foreach ($data as $key => $val){
    echo $key . '=>' . var_dump(empty($val)) . "\r\n";
}
//以上输出 '" "'，"null",true等为false,其它为true
is_null
$data=[""," ", 0, 0.0 ,"0", null, "null", true, false ,[]];
foreach ($data as $key => $val){
    echo $key . '=>' . var_dump(is_null($val)) . "\r\n";
}
//以上输出 null 为true,其它全为false

In addition, PHP7 has a quick way to judge which is the ?? and ?: syntax. You should also pay more attention to this

$a ?? 0; //相当于isset($a);
$a ?: 0; //相当于!empty($a);

Through the above example, you should understand these few There is a difference. As long as we pay more attention during development, we can choose the appropriate judgment function.

Conclusion

##isset: All non-null values ​​are true.

empty: "", 0,0.0,"0", null, false, array(), undefined var are all true.

is_null: The value is null and is true.

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