null和empty有什么区别? [英] What is the difference between null and empty?

问题描述

我对空和空的概念是陌生的.尽管我尽力了解它们之间的区别，但我更加困惑.我在 http://www.tutorialarena.com/blog/php-isset-上遇到了一篇文章vs-empty.php ，但是我仍然看不到在验证表单时何时使用isset和empty.看到我不明白它们之间的区别，我不想使用不正确的功能，也不想在其他领域使用这些功能.有人可以举一些例子来帮助我理解吗?我对编码非常陌生，因此如果有人可以给我提供真实的示例并同时使其足够简单以使noob能够理解，我将不胜感激.

I am new to the concept of empty and null. Whilst I have endeavoured to understand the difference between them, I am more confused. I came across an article at http://www.tutorialarena.com/blog/php-isset-vs-empty.php however I still don't see when you would use isset and empty when validating forms. Seeing that I don't grasp the difference, I don't want to be using the incorrect functions as well as not be able to use the functions in other areas. Can someone give examples that will help me understand? I am very new to coding so would appreciate if someone could give me real world examples and at the same time keep it simply enough for noob to follow.

推荐答案

如果变量没有值，并且指向内存中无处，则该变量为NULL.

A variable is NULL if it has no value, and points to nowhere in memory.

empty()更像是 empty 的字面意思，例如字符串""为空，但不是 NULL.

empty() is more a literal meaning of empty, e.g. the string "" is empty, but is not NULL.

以下事项被认为是 为空:

The following things are considered to be empty:

• "(一个空字符串)
• 0(0为整数)
• 0.0(浮点数为0)
• "0"(0作为字符串)
• NULL
• 假
• array()(一个空数组)
• var $ var; (已声明的变量，但在类中没有值)

• "" (an empty string)
• 0 (0 as an integer)
• 0.0 (0 as a float)
• "0" (0 as a string)
• NULL
• FALSE
• array() (an empty array)
• var $var; (a variable declared, but without a value in a class)

来源.

$a是NULL.

$a = ''是空，但不是NULL.

如果$a=''为空但不是NULL，则何时使用empty()函数以及何时使用isset()函数.

If $a='' is empty but not NULL, when do I use the empty() function and when do I use the isset() function.

isset() 将返回FALSE是变量所指向的到NULL.

isset() will return FALSE is the variable is pointing to NULL.

了解什么是空时，请使用empty()(请参见上面的列表).

Use empty() when you understand what is empty (look at the list above).

同样，当您说它在内存中没有指向时，那到底是什么意思?

Also when you say it points nowhere in memory, what does that mean exactly?

这意味着$str = ''将作为长度为0的字符串存储在内存中.

It means that $str = '' will be in memory as a string with length of 0.

如果是$str = NULL，则不会占用任何内存.

If it were $str = NULL, it would not occupy any memory.

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