Chapter 4. Arrays and Pointers

第四章 数组和指针

CONTENTS

The language defines two lower-level compound typesarrays and pointersthat are similar to vectors and iterators. Like a vector, an array holds a collection of objects of some type. Unlike vectors, arrays are fixed size; once an array is created, new elements cannot be added. Like iterators, pointers can be used to navigate among and examine the elements in an array.

C++ 语言提供了两种类似于 vector 和迭代器类型的低级复合类型——数组和指针。与 vector 类型相似，数组也可以保存某种类型的一组对象；而它们的区别在于，数组的长度是固定的。数组一经创建，就不允许添加新的元素。指针则可以像迭代器一样用于遍历和检查数组中的元素。

Modern C++ programs should almost always use vectors and iterators in preference to the lower-level arrays and pointers. Well-designed programs use arrays and pointers only in the internals of class implementations where speed is essential.

现代 C++ 程序应尽量使用 vector 和迭代器类型，而避免使用低级的数组和指针。设计良好的程序只有在强调速度时才在类实现的内部使用数组和指针。

Arrays are data structures that are similar to library vectors but are built into the language. Like a vector, an array is a container of objects of a single data type. The individual objects are not named; rather, each one is accessed by its position in the array.

数组是 C++ 语言中类似于标准库 vector 类型的内置数据结构。与 vector 类似，数组也是一种存储单一数据类型对象的容器，其中每个对象都没有单独的名字，而是通过它在数组中的位置对它进行访问。

Arrays have significant drawbacks compared to vectors: They are fixed size, and they offer no help to the programmer in keeping track of how big a given array is. There is no size operation on arrays. Similarly, there is no push_back to automatically add elements. If the array size needs to change, then the programmer must allocate a new, larger array and copy the elements into that new space.

与 vector 类型相比，数组的显著缺陷在于：数组的长度是固定的，而且程序员无法知道一个给定数组的长度。数组没有获取其容量大小的 size 操作，也不提供 push_back 操作在其中自动添加元素。如果需要更改数组的长度，程序员只能创建一个更大的新数组，然后把原数组的所有元素复制到新数组空间中去。

Programs that rely on built-in arrays rather than using the standard vector are more error-prone and harder to debug. 与使用标准 vector 类型的程序相比，依赖于内置数组的程序更容易出错而且难于调试。

Prior to the advent of the standard library, C++ programs made heavy use of arrays to hold collections of objects. Modern C++ programs should almost always use vectors instead of arrays. Arrays should be restricted to the internals of programs and used only where performance testing indicates that vectors cannot provide the necessary speed. However, there will be a large body of existing C++ code that relies on arrays for some time to come. Hence, all C++ programmers must know a bit about how arrays work.

在出现标准库之前，C++ 程序大量使用数组保存一组对象。而现代的 C++ 程序则更多地使用 vector 来取代数组，数组被严格限制于程序内部使用，只有当性能测试表明使用 vector 无法达到必要的速度要求时，才使用数组。然而，在将来一段时间之内，原来依赖于数组的程序仍大量存在，因此，C++ 程序员还是必须掌握数组的使用方法。