在关于C的一个有信誉的来源中,在讨论&操作符后给出了以下信息:

... 有点不幸的是,术语[地址的]仍然存在,因为它混淆了那些不知道地址是关于什么的人,并误导了那些知道地址的人:将指针视为地址通常会导致悲伤……

我读过的其他材料(来自同样有名望的来源,我想说)总是毫不掩饰地将指针和&操作符作为内存地址。我很愿意继续寻找事情的真相,但当有信誉的消息来源不同意时,这有点困难。

现在我有点困惑了——如果指针不是内存地址,那么它到底是什么?

P.S.

作者后来说:……不过,我将继续使用“地址”这个术语,因为发明一个不同的(术语)会更糟糕。


当前回答

你是对的,是理智的。通常,指针只是一个地址,因此您可以将其强制转换为整数并进行任何算术运算。

但有时指针只是地址的一部分。在一些体系结构上,指针被转换为一个增加了基数的地址或使用另一个CPU寄存器。

但是现在,在PC和ARM架构上,使用平面内存模型和原生编译的C语言,可以认为指针是指向一维可寻址RAM中某个位置的整数地址。

其他回答

它说“因为它让那些不知道地址是什么的人感到困惑”——而且,这是真的:如果你知道地址是什么,你就不会困惑了。从理论上讲,指针是一个指向另一个变量的变量,实际上保存着一个地址,即它所指向的变量的地址。我不知道为什么要隐瞒这个事实,这又不是什么高深的科学。如果你理解了指针,你就离理解计算机的工作原理更近了一步。去吧!

A pointer value is an address. A pointer variable is an object that can store an address. This is true because that's what the standard defines a pointer to be. It's important to tell it to C novices because C novices are often unclear on the difference between a pointer and the thing it points to (that is to say, they don't know the difference between an envelope and a building). The notion of an address (every object has an address and that's what a pointer stores) is important because it sorts that out.

然而,标准在特定的抽象层次上进行讨论。作者所说的那些“知道地址是关于什么的”,但对C不熟悉的人,必须在不同的抽象级别上学习地址——也许是通过编写汇编语言。不能保证C实现使用与cpu操作码相同的地址表示(在本文中称为“存储地址”),这些人已经知道。

He goes on to talk about "perfectly reasonable address manipulation". As far as the C standard is concerned there's basically no such thing as "perfectly reasonable address manipulation". Addition is defined on pointers and that is basically it. Sure, you can convert a pointer to integer, do some bitwise or arithmetic ops, and then convert it back. This is not guaranteed to work by the standard, so before writing that code you'd better know how your particular C implementation represents pointers and performs that conversion. It probably uses the address representation you expect, but it it doesn't that's your fault because you didn't read the manual. That's not confusion, it's incorrect programming procedure ;-)

简而言之,C使用了比作者更抽象的地址概念。

The author's concept of an address of course is also not the lowest-level word on the matter. What with virtual memory maps and physical RAM addressing across multiple chips, the number that you tell the CPU is "the store address" you want to access has basically nothing to do with where the data you want is actually located in hardware. It's all layers of indirection and representation, but the author has chosen one to privilege. If you're going to do that when talking about C, choose the C level to privilege!

Personally I don't think the author's remarks are all that helpful, except in the context of introducing C to assembly programmers. It's certainly not helpful to those coming from higher level languages to say that pointer values aren't addresses. It would be far better to acknowledge the complexity than it is to say that the CPU has the monopoly on saying what an address is and thus that C pointer values "are not" addresses. They are addresses, but they may be written in a different language from the addresses he means. Distinguishing the two things in the context of C as "address" and "store address" would be adequate, I think.

指针是一种在C/ c++中本地可用的变量类型,包含一个内存地址。像任何其他变量一样,它有自己的地址并占用内存(数量是特定于平台的)。

由于混淆,您将看到的一个问题是试图通过简单地按值传递指针来更改函数中的引用。这将复制函数作用域内的指针,对这个新指针“指向”的地方的任何更改都不会改变调用该函数的作用域内指针的引用。为了修改函数中的实际指针,通常会将一个指针传递给另一个指针。

Come to think about it, I think it's a matter of semantics. I don't think the author is right, since the C standard refers to a pointer as holding an address to the referenced object as others have already mentioned here. However, address!=memory address. An address can be really anything as per C standard although it will eventually lead to a memory address, the pointer itself can be an id, an offset + selector (x86), really anything as long as it can describe (after mapping) any memory address in the addressable space.

快速总结:C地址是一个值,通常表示为具有特定类型的机器级内存地址。

非限定词“指针”有歧义。C语言有指针对象(变量)、指针类型、指针表达式和指针值。

使用“指针”这个词来表示“指针对象”是非常常见的,这可能会导致一些混淆——这就是为什么我试图将“指针”作为形容词而不是名词使用。

C标准,至少在某些情况下,使用“指针”这个词来表示“指针值”。例如,malloc的描述说它“返回空指针或指向已分配空间的指针”。

那么C中的地址是什么呢?它是一个指针值,即某个特定指针类型的值。(除了空指针值不一定被称为“地址”,因为它不是任何东西的地址)。

标准对一元&操作符的描述说它“产生其操作数的地址”。在C标准之外,单词“address”通常用于指(物理或虚拟)内存地址,通常是一个单词大小(无论给定系统上的“word”是什么)。

C“地址”通常实现为机器地址——就像C int值通常实现为机器字一样。但是C地址(指针值)不仅仅是一个机器地址。它是一个通常表示为机器地址的值,它是一个具有特定类型的值。