PHP中的empty()，isset()和is_null()函数有什么区别? [英] What is the difference between empty() , isset() and is_null() function in php?

问题描述

我做了很多研究，但无法找到这三个之间的区别.因此，我做了一个简短的例子，希望对我们有所帮助.

I did lot of research but was unable to find the difference between these three. So I have done a short example I hope that will we helpful.

这是这三个表格的表述

Case             Empty()        isset()     is_null()
1. $a=NULL         1              0             1

2. Not exists      1              0         1/Warning

3. $a=''           1              1             0

4. $a='NULL'       0              1             0

5. $a='testing'    0              1             0

这是实现它的代码.

推荐答案

PHP具有可用于测试变量值的不同功能.为此，三个有用的函数是 isset()， empty()和 is_null().所有这些函数都返回一个布尔值.如果未正确使用这些功能，可能会导致意外结果.

PHP has different functions which can be used to test the value of a variable. Three useful functions for this are isset(), empty() and is_null(). All these function return a boolean value. If these functions are not used in correct way they can cause unexpected results.

isset()和 empty()通常被视为相反的函数，但这并不总是正确的.

isset() and empty() are often viewed as functions that are opposite, however this is not always true.

isset — 确定是否设置了变量并且该变量不为NULL

换句话说，仅当变量不为null时，它才返回true.

In other words, it returns true only when the variable is not null.

空-确定变量是否为空

换句话说，如果变量为空字符串，false，array()，NULL，"0"，0和未设置的变量，则它将返回true.

In other words, it will return true if the variable is an empty string, false, array(), NULL, "0?, 0, and an unset variable.

is_null — 查找变量是否为NULL

换句话说，仅当变量为null时，它才返回true.is_null()与isset()相反，不同之处在于isset()可以应用于未知变量，但is_null()仅适用于声明的变量

In other words, it returns true only when the variable is null. is_null() is opposite of isset(), except for one difference that isset() can be applied to unknown variables, but is_null() only to declared variables

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