简单地说，指针实际上是分割机制的偏移部分，分割后转换为线性地址，分页后转换为物理地址。物理地址实际上是从ram中寻址的。

       Selector  +--------------+         +-----------+
      ---------->|              |         |           |
                 | Segmentation | ------->|  Paging   |
        Offset   |  Mechanism   |         | Mechanism |
      ---------->|              |         |           |
                 +--------------+         +-----------+
        Virtual                   Linear                Physical

指针只是另一个变量，它通常包含另一个变量的内存地址。指针是一个变量，它也有一个内存地址。

A pointer, like any other variable in C, is fundamentally a collection of bits which may be represented by one or more concatenated unsigned char values (as with any other type of cariable, sizeof(some_variable) will indicate the number of unsigned char values). What makes a pointer different from other variables is that a C compiler will interpret the bits in a pointer as identifying, somehow, a place where a variable may be stored. In C, unlike some other languages, it is possible to request space for multiple variables, and then convert a pointer to any value in that set into a pointer to any other variable within that set.

Many compilers implement pointers by using their bits store actual machine addresses, but that is not the only possible implementation. An implementation could keep one array--not accessible to user code--listing the hardware address and allocated size of all of the memory objects (sets of variables) which a program was using, and have each pointer contain an index into an array along with an offset from that index. Such a design would allow a system to not only restrict code to only operating upon memory that it owned, but also ensure that a pointer to one memory item could not be accidentally converted into a pointer to another memory item (in a system that uses hardware addresses, if foo and bar are arrays of 10 items that are stored consecutively in memory, a pointer to the "eleventh" item of foo might instead point to the first item of bar, but in a system where each "pointer" is an object ID and an offset, the system could trap if code tried to index a pointer to foo beyond its allocated range). It would also be possible for such a system to eliminate memory-fragmentation problems, since the physical addresses associated with any pointers could be moved around.

Note that while pointers are somewhat abstract, they're not quite abstract enough to allow a fully-standards-compliant C compiler to implement a garbage collector. The C compiler specifies that every variable, including pointers, is represented as a sequence of unsigned char values. Given any variable, one can decompose it into a sequence of numbers and later convert that sequence of numbers back into a variable of the original type. Consequently, it would be possible for a program to calloc some storage (receiving a pointer to it), store something there, decompose the pointer into a series of bytes, display those on the screen, and then erase all reference to them. If the program then accepted some numbers from the keyboard, reconstituted those to a pointer, and then tried to read data from that pointer, and if user entered the same numbers that the program had earlier displayed, the program would be required to output the data that had been stored in the calloc'ed memory. Since there is no conceivable way the computer could know whether the user had made a copy of the numbers that were displayed, there would be no conceivable may the computer could know whether the aforementioned memory might ever be accessed in future.

C或c++指针与简单内存地址的另一个不同之处是，我在其他答案中没有看到不同的指针类型(尽管考虑到它们的总大小，我可能忽略了它)。但它可能是最重要的一个，因为即使是经验丰富的C/ c++程序员也会被它绊倒:

编译器可能会假设不兼容类型的指针不指向相同的地址，即使它们很明显指向相同的地址，这可能会导致简单的pointer==address模型不可能出现的行为。考虑以下代码(假设sizeof(int) = 2*sizeof(short)):

unsigned int i = 0;
unsigned short* p = (unsigned short*)&i;
p[0]=p[1]=1;

if (i == 2 + (unsigned short)(-1))
{
  // you'd expect this to execute, but it need not
}

if (i == 0)
{
  // you'd expect this not to execute, but it actually may do so
}

注意，char*有一个例外，所以使用char*操作值是可能的(尽管不是很可移植)。

以下是我过去是如何向一些困惑的人解释的: 指针有两个影响其行为的属性。它有一个值(在典型环境中)是一个内存地址，还有一个类型(告诉您它所指向的对象的类型和大小)。

例如，给定:

union {
    int i;
    char c;
} u;

你可以有三个不同的指针都指向同一个对象:

void *v = &u;
int *i = &u.i;
char *c = &u.c;

如果你比较这些指针的值，它们都是相等的:

v==i && i==c

但是，如果对每个指针加1，就会发现它们所指向的类型变得相关了。

i++;
c++;
// You can't perform arithmetic on a void pointer, so no v++
i != c

此时，变量i和c将具有不同的值，因为i++使i包含下一个可访问的整数的地址，而c++使c指向下一个可寻址的字符。通常，整数比字符占用更多的内存，所以在它们都加一之后，i的值将比c的值更大。

指针是一个保存内存地址的变量，而不是地址本身。但是，您可以解除对指针的引用-并访问内存位置。

例如:

int q = 10; /*say q is at address 0x10203040*/
int *p = &q; /*means let p contain the address of q, which is 0x10203040*/
*p = 20; /*set whatever is at the address pointed by "p" as 20*/

就是这样。就是这么简单。

一个演示我所说内容的程序，其输出如下:

http://ideone.com/rcSUsb

程序:

#include <stdio.h>

int main(int argc, char *argv[])
{
  /* POINTER AS AN ADDRESS */
  int q = 10;
  int *p = &q;

  printf("address of q is %p\n", (void *)&q);
  printf("p contains %p\n", (void *)p);

  p = NULL;
  printf("NULL p now contains %p\n", (void *)p);
  return 0;
}