我可以对空指针使用指针算术吗? [英] Can I use pointer arithmetic on pointers to void pointers?

问题描述

我知道您不能在void指针上使用指针算术，但是理论上您可以在指向void指针的指针上进行指针算术，因为sizeof(void *)会得出一个指针在系统上占用多少字节的答案?

I know you can't utilize pointer arithmetic on void pointers, but could you theoretically do pointer arithmetic on pointers to void pointers, since sizeof(void *) would yield an answer of how many bytes a pointer takes on your system?

推荐答案

在void*上不允许使用指针算术，因为void是不完整的对象类型.

Pointer arithmetic is not permitted on void* because void is an incomplete object type.

来自C委员会N1570草案:

From C Committee draft N1570:

6.5.6加法运算符
...
2.另外，两个操作数都应具有算术类型，或者一个操作数应是指向完整对象类型的指针，而另一个操作数应具有整数类型.

6.5.6 Additive operators
...
2. For addition, either both operands shall have arithmetic type, or one operand shall be a pointer to a complete object type and the other shall have integer type.

但是在void**上允许使用，因为void*不是不完整的对象类型.就像一个指向字符类型的指针.

But it is permitted on void** because void* is NOT an incomplete object type. It is like a pointer to a character type.

6.2.5类型
...
19. 无效类型包含一组空值； 这是一个不完整的对象类型，无法完成.
...
28. 指向void的指针应具有与相同的表示和对齐要求 指向字符类型的指针.

6.2.5 Types
...
19. The void type comprises an empty set of values; it is an incomplete object type that cannot be completed.
...
28. A pointer to void shall have the same representation and alignment requirements as a pointer to a character type.

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