How to determine the type of a variable in PHP

There are various types of variables in PHP, and different types have different judgment methods. Here is a summary of some judgments of variable types in PHP.

1. gettype()
gettype will return the following values ​​​​according to the parameter type
"boolean" (from PHP 4)
"integer"
"double" (if it is float then returns "double" instead of "float")
"string"
"array"
"object"
"resource" (from PHP 4)
"NULL" (from PHP 4 onwards)
"unknown type"

For example:
gettype('1'); returns string
and gettype(1); returns integer

2. The type judgment that comes with PHP is as follows

isset():                        //变量是否已经声明
empty():                        //变量是否为空
defined():　　　　　　　　　　　　　　　　　　　　　　　//常量是否已经定义 define()
array_key_exists(mixed key, array search):        //检查给定的键名或索引是否存在于数组中
is_numeric ( mixed var ):                //检测变量是 否为数字或数字字符串
is_bool():            // 检测变量是否是布尔型
is_float():            // 检测变量是否是浮点型 和is_double，is_real()都一样的用法
is_int():            // 检测变量是否是整数is_integer() 一样的 用法
is_string():            // 检测变量是否是字符串
is_object():            // 检测变量是否是一个对象
is_array():            // 检测变量是否是数组
is_null():            // 检测变量是否为 NULL 值是否是NULL大小写敏感

3. The difference between PHP empty, isset and isnull

empty

If the variable has a non-empty or non-zero value, empty() returns FALSE. In other words, "", 0, "0", NULL, FALSE, array(), var $var, undefined; and objects without any attributes will be considered empty. If var is empty, TRUE will be returned. .

isset

Returns TRUE if the variable exists (not NULL), otherwise returns FALSE (including undefined). The variable value is set to: null, and the return value is also false; after unsetting a variable, the variable is canceled. Note that isset handles NULL value variables specially.

is_null

Check whether the incoming value [value, variable, expression] is null. Only if one variable is defined and its value is null will it return TRUE. Others will return FALSE [An error will occur after undefined variables are passed in! 】

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