C语言指针教程：从入门到精通

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本文档是关于C语言指针的教程，由Ted Jensen编写，适用于初学者。版本1.2，发布日期为2003年9月，作者将该材料置于公共领域，便于广泛传播。这份教程主要涵盖了以下十个章节： 1. **引言**：文档的目标是帮助C编程语言的新手理解指针的概念，针对的是那些在学习过程中对指针基础感到困惑的程序员。作者认识到在许多讨论C语言的论坛上，新手们常常难以掌握指针的精髓，因此他撰写了这个通俗易懂且包含大量实例的指南。 2. **第一章：什么是指针?** - 这部分会解释指针的基本概念，包括指针变量、它们如何存储内存地址以及为何在程序中使用它们。 3. **第二章：指针类型与数组** - 探讨不同类型的指针（如整型、字符型等）以及它们如何关联到数组，使读者理解数组名本质上是其第一个元素的地址。 4. **第三章：指针与字符串** - 介绍如何使用指针操作字符串，包括字符数组和动态分配内存的情况。 5. **第四章：更多关于字符串** - 深入探讨字符串处理技巧，可能涉及指针的索引和修改字符串的操作。 6. **第五章：指针与结构体** - 指针如何在结构体中使用，以及如何通过指针访问和修改结构体成员。 7. **第六章：更多的字符串和字符串数组** - 提供更多的例子，展示如何处理多字符串和数组的指针操作。 8. **第七章：更深入的多维数组** - 学习如何使用指针遍历和操作多维数组。 9. **第八章：指向数组的指针** - 讨论指针作为数组的别名，以及它们在函数参数传递中的作用。 10. **第九章：指针与动态内存分配** - 介绍如何使用`malloc()`和`free()`等函数进行内存管理，以及如何正确地使用指针与动态分配的内存。 11. **第十章：指向函数的指针** - 指针作为函数的参数和返回值，以及如何使用函数指针来执行通用操作。 12. **附录**：结束语，可能包含总结要点、进一步的学习资源或者作者的联系方式，鼓励读者继续探索指针的世界。这本教程的目的是通过实用的实例和清晰的语言，让初学者能够扎实地建立起对C语言指针的理解，从而更好地进行编程实践。

CHAPTER 2: Pointer types and Arrays

Okay, let's move on. Let us consider why we need to identify the type of variable that a

pointer points to, as in:

int *ptr;

One reason for doing this is so that later, once ptr "points to" something, if we write:

*ptr = 2;

the compiler will know how many bytes to copy into that memory location pointed to by

ptr. If ptr was declared as pointing to an integer, 2 bytes would be copied, if a long, 4

bytes would be copied. Similarly for floats and doubles the appropriate number will be

copied. But, defining the type that the pointer points to permits a number of other

interesting ways a compiler can interpret code. For example, consider a block in memory

consisting if ten integers in a row. That is, 20 bytes of memory are set aside to hold 10

integers.

Now, let's say we point our integer pointer ptr at the first of these integers. Furthermore

lets say that integer is located at memory location 100 (decimal). What happens when we

write:

ptr + 1;

Because the compiler "knows" this is a pointer (i.e. its value is an address) and that it

points to an integer (its current address, 100, is the address of an integer), it adds 2 to ptr

instead of 1, so the pointer "points to" the next integer, at memory location 102.

Similarly, were the ptr declared as a pointer to a long, it would add 4 to it instead of 1.

The same goes for other data types such as floats, doubles, or even user defined data

types such as structures. This is obviously not the same kind of "addition" that we

normally think of. In C it is referred to as addition using "pointer arithmetic", a term

which we will come back to later.

Similarly, since ++ptr and ptr++ are both equivalent to ptr + 1 (though the point in the

program when ptr is incremented may be different), incrementing a pointer using the

unary ++ operator, either pre- or post-, increments the address it stores by the amount

sizeof(type) where "type" is the type of the object pointed to. (i.e. 2 for an integer, 4 for a

long, etc.).

Since a block of 10 integers located contiguously in memory is, by definition, an array of

integers, this brings up an interesting relationship between arrays and pointers.

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