C语言 定义 NULL 和 NULL_POINTER 的正确方法？
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Correct way of defining NULL and NULL_POINTER?
提问by Niklas
As far as I know, Cdefines NULLlike this:
据我所知，C定义NULL如下：
#define NULL ( (void *) 0)
Then, how should we define NULL_POINTER? I defined it the same in my program and it worked, but I suppose that is just a coincidence:
那么，我们应该如何定义NULL_POINTER？我在我的程序中对其进行了相同的定义并且它起作用了，但我认为这只是巧合：
#define NULL_POINTER ( (void *) 0)
What would be the logical definition, if any ?
如果有的话，逻辑定义是什么？
回答by Yu Hao
#define NULL ( (void *) 0)
and
和
#define NULL 0
are both valid. If you need to implement your own macro for null pointer, the same rule applies.
都是有效的。如果您需要为空指针实现自己的宏，则适用相同的规则。
C11(ISO/IEC 9899:201x) §6.3.2.3 PointersSection 3
An integer constant expression with the value
0, or such an expression cast to typevoid *, is called a null pointer constant
C11(ISO/IEC 9899:201x) §6.3.2.3指针第 3 节
带有值的整数常量表达式
0，或转换为类型的此类表达式void *，称为空指针常量。
回答by Dayal rai
It is only in pointer contexts that NULLand 0are equivalent. NULLshould not be used when another kind of 0is required, even though it might work, because doing so sends the wrong stylistic message. (Furthermore, ANSI allows the definition of NULLto be ((void *)0), which will not work at all in non-pointer contexts.) In particular, do not use NULLwhen the ASCII null character (NUL) is desired. Provide your own definition
只有在指针上下文中NULL和0是等价的。NULL不应在需要另一种类型时0使用，即使它可能有效，因为这样做会发送错误的风格信息。（此外，ANSI允许的定义NULL是((void *)0)，这将在所有的在非指针上下文不工作。）特别是，不使用NULL该ASCII空字符（NUL）期望时。提供您自己的定义
#define NUL '##代码##'
NULLshould be used only as a pointer constant.
NULL应仅用作指针常量。
