是否有任何物理部分的内存地址为NULL（0）？ [英] Is there any physical part of memory with the address of NULL(0)?

问题描述

我知道有一个古老的说法，当你想表明这个特定的指针不指向任何应该设置为NULL（实际上是0），但我想知道是不是实际上有一个物理部分的内存NULL的地址（0）？

I know there's an old saying when you want to indicate this specific pointer doesn't point to anything it should be set to NULL(actually 0), but I'm wondering isn't there actually a physical part of memory with the address of NULL(0) ?

推荐答案

总有一个物理地址为0（但它可能不一定映射到物理RAM），但在典型的平台上，任何访问通常将在虚拟地址空间中执行（如jweyrich指出的，可以使用 mmap 等直接映射物理地址空间），所以任何读/写地址0的尝试都会引发某种异常。

There is always a physical address of 0 (but it may not necessarily map onto physical RAM), but on a typical platform any accesses will typically be performed in a virtual address space (as jweyrich points out below, you can use mmap and so on to directly map the physical address space), so any attempt to read/write to address 0 will raise an exception of some kind.

在更简单的处理器（例如微控制器等）可能没有这样的保护，所以如果你尝试写入地址0，就没有什么可以抓住你。

On simpler processors (think microcontrollers and so on), there may be no such protection, so if you attempt to write to address 0, there'll be nothing to catch you.

注意一个空指针不一定必须指向地址0;唯一的保证是它将比较等于整数值 0 。

Note also that a null pointer doesn't necessarily have to point at address 0; the only guarantee is that it will compare equal to integer value 0.

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