Summary of common judgment conditions in PHP

Types of commonly used judgment conditions

• Variables such as: $var

• isset()

• empty()

• Comparison operators such as: > < == != === !==

• ##Logical operations Symbols such as:! && || or and

• Specific type judgment, for example: is_null()/is_array()/is_int(), etc.

Variable

• No matter what type the variable is, it will be converted to bool type

• Empty strings and empty arrays are false

• The value 0 and the string "0" are both false

• The NULL type is false

NULL类型有三种情况：
1、定义并赋值为null
2、定义不赋值
3、不定义（不存在的）

isset()

• is mainly used to determine the NULL type. For other types, no matter what the value is, it is true

• and is_null() are a pair of opposite functions.

empty()

• and variables are a pair that have exactly the opposite effect

• The range of judgment Larger than isset()

• Empty strings and empty arrays are both true

• The value 0 and the string "0" are both true

• NULL types are all true

Types of commonly used judgment conditions

• Variable example: $var

• isset()

• empty()

• Comparison operators such as: > < == != === !==

• Logical operators such as: ! && || or and

• Specific type judgment, for example: is_null()/is_array()/is_int(), etc.

Variable

• No matter what type the variable is, it will be converted to bool type

• Empty strings and empty arrays are false

• The value 0 and the string "0" are both false

• The NULL type is false

NULL类型有三种情况：
1、定义并赋值为null
2、定义不赋值
3、不定义（不存在的）

isset()

• is mainly used to determine the NULL type. For other types, no matter what the value is, it is true

• and is_null() are a pair of opposite functions.

empty()

• and variables are a pair that have exactly the opposite effect

• The range of judgment Larger than isset()

• Empty strings and empty arrays are both true

• The value 0 and the string "0" are both true

• NULL types are all true

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