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Home Backend Development PHP Problem How to determine if a field is not empty in php

How to determine if a field is not empty in php

Feb 21, 2023 am 09:18 AM
php Field

php method to determine whether a field is empty: 1. Use the isset method to determine whether the variable has been initialized; 2. Use the empty method to detect whether the variable is "empty"; 3. Judge through the "var == null" method Whether the variable is "null"; 4. Use the is_null method to detect whether the variable is "null"; 5. Use the "var === null" method to detect whether the variable is "null", and the type of the variable must also be "null".

How to determine if a field is not empty in php

The operating environment of this tutorial: Windows 10 system, PHP version 8.1, DELL G3 computer

How to determine if a field is not empty in php ?

5 ways to determine whether the variable is empty in PHP

  • ##isset function: determine whether the variable is initialized

Note: It does not determine whether the variable is empty, but can be used to determine whether the elements in the array have been defined.

Note: When using isset to determine whether an array element has been initialized, its efficiency is about 4 times higher than array_key_exists.

<?php
    //$a = &#39;&#39;;
    //$a = false;
    $a[&#39;c&#39;] = &#39;&#39;;
    if (!isset($a)) echo &#39;$a 未被初始化&#39; . "<br/>";
    if (!isset($b)) echo &#39;$b 未被初始化&#39; . "<br/>";
    if (isset($a[&#39;c&#39;])) echo &#39;$a 已經(jīng)被初始化&#39; . "<br/>";
//結(jié)果
// $b 未被初始化
// $a 已經(jīng)被初始化

  • empty() function: detect whether the variable is "empty"

Description: Any uninitialized variable, the value is 0 or false or empty string "" or null variable, empty array, object without any attributes, empty(variable) == true.

Note 1: Uninitialized variables can also be detected as "empty" by empty.

Note 2: empty can only detect variables, not statements.

<?php
$a = 0;
$b = &#39;&#39;;
$c = array();
if (empty($a)) echo &#39;$a 為空&#39; . "<br/>";
if (empty($b)) echo &#39;$b 為空&#39; . "<br/>";
if (empty($c)) echo &#39;$c 為空&#39; . "<br/>";
if (empty($d)) echo &#39;$d 為空&#39; . "<br/>";
//結(jié)果
// $a 為空
// $b 為空
// $c 為空
// $d 為空
var_dump(empty(null));
var_dump(empty(0));
var_dump(empty(&#39;&#39;));
var_dump(empty([]));
//結(jié)果
// bool(true)
// bool(true)
// bool(true)
// bool(true)

  • var == null Function: Determine whether the variable is "empty"

Description: The value is 0 or false or empty string" ” or null variables and empty arrays will be judged as null.

Note: The significant difference from empty is that var == null will report an error when the variable is not initialized.

<?php
$a = 0;
$b = array();
if ($a == null) echo &#39;$a 為空&#39; . "";
if ($b == null) echo &#39;$b 為空&#39; . "";
if ($c == null) echo &#39;$c 為空&#39; . "";
// 顯示結(jié)果為
// $a 為空
// $b 為空
// Undefined variable: c

  • is_null function: detect whether the variable is "null"

Description: When the variable is assigned a value of "null", the detection result is true.

Note 1: null is not case-sensitive: a=null;a=null;a = NULL makes no difference.

Note 2: Only when the value of the variable is "null", the detection result is true. 0, empty string, false, and empty array are all detected as false.

Note 3: When the variable is not initialized, the program will report an error.

<?php
$a = null;
$b = false;
if (is_null($a)) echo &#39;$a 為NULL&#39; . "";
if (is_null($b)) echo &#39;$b 為NULL&#39; . "";
if (is_null($c)) echo &#39;$c 為NULL&#39; . "";
// 顯示結(jié)果為
// $a 為NULL
// Undefined variable: c

  • var === null function: detect whether the variable is "null", and the type of the variable must also be "null"

Note: When a variable is assigned a value of "null" and the type of the variable is also "null", the detection result is true.

*Note 1: When judging "null", equal to is_null has the same effect.

*Note 2: When the variable is not initialized, the program will report an error.

Summary:

In PHP, "NULL" and "empty" are two concepts.

isset is mainly used to determine whether the variable has been initialized.

empty can judge variables with values ??of "false", "empty", "0", "NULL", and "uninitialized" as TRUE.

is_null only evaluates variables with a value of "NULL" as TRUE.

var == null Judges variables with values ??of "false", "empty", "0", and "NULL" as TRUE.

var === null Only variables with a value of "NULL" are judged as TRUE.

Note: When judging whether a variable is really "NULL", is_null is mostly used to avoid interference from "false", "0" and other values.

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