STL介绍

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翻译的一篇SGI STL文档还要好多不太会翻译，以后在慢慢领悟吧！

Introduction to the Standard Template Library

标准模板库简介

The Standard Template Library, or STL, is a C++ library of container classes, algorithms, and iterators; it provides many of the basic algorithms and data structures of computer science. The STL is a generic library, meaning that its components are heavily parameterized: almost every component in the STL is a template. You should make sure that you understand how templates work in C++ before you use the STL. 标准模板库，或STL，是一个包括容器类，算法和迭代器的C++库；它提供了许多计算机的基本算法和数据结构。STL是一个泛型库，这意味这它是由很深的参数机制实现的：几乎每一个STL的组件都是模板。你在使用STL之前应该确信你已经懂得了C++的模板。

Containers and algorithms

容器和算法

Like many class libraries, the STL includes container classes: classes whose purpose is to contain other objects. The STL includes the classes vector, list, deque, set, multiset, map, multimap, hash_set, hash_multiset, hash_map, and hash_multimap. Each of these classes is a template, and can be instantiated to contain any type of object. You can, for example, use a vector<int> in much the same way as you would use an ordinary C array, except that vector eliminates the chore of managing dynamic memory allocation by hand. 像许多类库，STL包括容器类：用于包含其他类对象的类。STL包括的容器类有vector, list, deque, set, multiset, map, multimap, hash_set, hash_multiset, hash_map,和hash_multimap。每一个容器类都是模板，而且可以被实例化去包含任何类型的对象。例如你可以使用vector<int>像使用一个原生的C数组，出此之外vector还消除了一些手动动态内存管理的琐碎事情。
       vector<int> v(3);             // Declare a vector of 3 elements.
       v[0] = 7;
       v[1] = v[0] + 3;
       v[2] = v[0] + v[1];           // v[0] == 7, v[1] == 10, v[2] == 17  
       vector<int> v(3);             // 声明一个包含三个元素的vector.
       v[0] = 7;
       v[1] = v[0] + 3;
       v[2] = v[0] + v[1];           // v[0] == 7, v[1] == 10, v[2] == 17


The STL also includes a large collection of algorithms that manipulate the data stored in containers. You can reverse the order of elements in a vector, for example, by using the reverse algorithm.

STL也包括一个很大的算法集合用于处理存储在容器的数据。例如你可以通过使用reverse算法倒序保存在vector中的元素。
       reverse(v.begin(), v.end()); // v[0] == 17, v[1] == 10, v[2] == 7


There are two important points to notice about this call to reverse. First, it is a global function, not a member function. Second, it takes two arguments rather than one: it operates on a range of elements, rather than on a container. In this particular case the range happens to be the entire container v.

在使用reverse时有两个重要点值得注意,第一点是它是一个全局函数，而不是一个成员函数；第二点是它包括两个参数而不是一个参数，容器元素的边界而不是容器。在我们这个例子中，边界即为整个容器。 The reason for both of these facts is the same: reverse, like other STL algorithms, is decoupled from the STL container classes. This means that reverse can be used not only to reverse elements in vectors, but also to reverse elements in lists, and even elements in C arrays. The following program is also valid. 这两点其实是一样的：reverse，像其他的STL算法，是与STL容器类，这意味这reverse不仅可以用于倒序vectors中的元素，还可以用于lists，甚至用于C数组。下面的程序是合法的。
       double A[6] = { 1.2, 1.3, 1.4, 1.5, 1.6, 1.7 };
       reverse(A, A + 6);
       for (int i = 0; i < 6; ++i)
         cout << “A[“ << i << “] = “ << A[i];


This example uses a range, just like the example of reversing a vector: the first argument to reverse is a pointer to the beginning of the range, and the second argument points one element past the end of the range. This range is denoted [A, A + 6); the asymmetrical notation is a reminder that the two endpoints are different, that the first is the beginning of the range and the second is one past the end of the range.

这个例子中使用的区间，就像在倒序vector中使用的：第一个参数是指向倒序的区间的开始，第二个参数是指向超过区间的第一个元素。这个区间表示的是[A，A+6],非对称的符号提示两点区间端点是不同的，第一个端点是区间的起始点，第二个是超过区间的第一个点。

Iterators

迭代器

In the example of reversing a C array, the arguments to reverse are clearly of type double*. What are the arguments to reverse if you are reversing a vector, though, or a list? That is, what exactly does reverse declare its arguments to be, and what exactly do v.begin() and v.end() return? 在倒序C数组的例子中，传递给reverse的参数比较清晰就是double*。那么当你倒序一个vector或者list时传递给reverse的参数是什么呢？也就是，reverse声明的参数类型到底是什么，v.begin()和v.end()返回的是什么呢？ The answer is that the arguments to reverse are iterators, which are a generalization of pointers. Pointers themselves are iterators, which is why it is possible to reverse the elements of a C array. Similarly, vector declares the nested types iterator and const_iterator. In the example above, the type returned by v.begin() and v.end() is vector<int>::iterator. There are also some iterators, such as istream_iterator and ostream_iterator, that aren’t associated with containers at all. 答案是传递给reverse的参数是迭代器，一个泛型指针。指向它们自己的是迭代器，为什么可以倒序C数组中的元素呢。类似地，vector声明了内嵌类型的iterator and const_iterator。在上面的例子中，v.begin()和v.end()返回的类型是vector<int>::iterator。还有一些其他的迭代器，比如istream_iterator和ostream_iterator，它们并没有和容器相关联。 Iterators are the mechanism that makes it possible to decouple algorithms from containers: algorithms are templates, and are parameterized by the type of iterator, so they are not restricted to a single type of container. Consider, for example, how to write an algorithm that performs linear search through a range. This is the STL’s find algorithm. 迭代器是一种使得算法与容器分离的机制：算法是模板，被迭代器的类型参数化，所以他们没有限制非要在一个单独类型的容器上。考虑这样一个例子，怎么写一个算法实现在一个区间上线性查找。STL的find即是这样的算法：       template <class InputIterator, class T>
       InputIterator find(InputIterator first, InputIterator last, const T& value) {
           while (first != last && first != value) ++first;
           return first;
       }
find要求三个参数：两个迭代器定义了一个区间，一个value用于在区间中查找。它在区间[first,last)中检查每一个迭代器，从开始到结束，在找到一个指向value的迭代器或者到达区间尾时停止。


Find takes three arguments: two iterators that define a range, and a value to search for in that range. It examines each iterator in the range [first, last), proceeding from the beginning to the end, and stops either when it finds an iterator that points to value or when it reaches the end of the range.

First and last are declared to be of type InputIterator, and InputIterator is a template parameter. That is, there isn’t actually any type called InputIterator: when you call find, the compiler substitutes the actual type of the arguments for the formal type parameters InputIterator and T. If the first two arguments to find are of type int and the third is of type int, then it is as if you had called the following function.

First和last被声明为InputIterator类型，是一个模板参数类型。实际上并没有叫做InputItearot的类型：当你调用find时，编译器会用实参类型替换型参InputIteartor和T。假如传递给find的前面两个参数是int，第三个参数是int的话，实际上你调用的函数是下面这样的：
       int find(int first, int last, const int& value) {
           while (first != last && *first != value) ++first;
           return first;
       }


## Concepts and Modeling

概念和模型

One very important question to ask about any template function, not just about STL algorithms, is what the set of types is that may correctly be substituted for the formal template parameters. Clearly, for example, int or double may be substituted for find‘s formal template parameter InputIterator. Equally clearly, int or double may not: find uses the expression *first, and the dereference operator makes no sense for an object of type int or of type double. The basic answer, then, is that find implicitly defines a set of requirements on types, and that it may be instantiated with any type that satisfies those requirements. Whatever type is substituted for InputIterator must provide certain operations: it must be possible to compare two objects of that type for equality, it must be possible to increment an object of that type, it must be possible to dereference an object of that type to obtain the object that it points to, and so on. 一个关于模板函数的非常重要的问题，不仅仅是STL算法，是正确的替换形式模板参。明显地，例如，int和double也许会替换find的形式模板参数Input- Iterato。同样地，int或者double也许不会：find使用表达式*first，解引用运算符对一个int或者double类型没有任何意义。一个简单的答案是，find也许显示定义了一个需求类型集合，它会这些参数能满足需求的时候被实例化（也就是不满足要求的会报错了）。能够替换InputIterator的参数必须提供能够以下操作：它必须可以比较两个类型是否相等，它必须可以自增，而且还可以解引用获得它指向的元素，等等。 Find isn’t the only STL algorithm that has such a set of requirements; the arguments to for_each and count, and other algorithms, must satisfy the same requirements. These requirements are sufficiently important that we give them a name: we call such a set of type requirements a concept, and we call this particular concept Input Iterator. We say that a type conforms to a concept, or that it is a model of a concept, if it satisfies all of those requirements. We say that int is a model of Input Iterator because int provides all of the operations that are specified by the Input Iterator requirements. STL算法中并不是只要Find有这样的一个需求集合，for_each和count的参数，还要其他的算法同样需要满足同样的要求。这些需求是足够重要的，我们给他们起个名字：我们称这样的类型需求集合为概念，这样一个特殊的概念叫做输入迭代器。我们称满足这样要求的概念为一个模型。Int是一个Input Iterator因为int提供了所有Input Iterator要求的的操作。 Concepts are not a part of the C++ language; there is no way to declare a concept in a program, or to declare that a particular type is a model of a concept. Nevertheless, concepts are an extremely important part of the STL. Using concepts makes it possible to write programs that cleanly separate interface from implementation: the author of find only has to consider the interface specified by the concept Input Iterator, rather than the implementation of every possible type that conforms to that concept. Similarly, if you want to use find, you need only to ensure that the arguments you pass to it are models of Input Iterator. This is the reason why find and reverse can be used with lists, vectors, C arrays, and many other types: programming in terms of concepts, rather than in terms of specific types, makes it possible to reuse software components and to combine components together.

Refinement

精巧

Input Iterator is, in fact, a rather weak concept: that is, it imposes very few requirements. An Input Iterator must support a subset of pointer arithmetic (it must be possible to increment an Input Iterator using prefix and postfix operator++), but need not support all operations of pointer arithmetic. This is sufficient for find, but some other algorithms require that their arguments satisfy additional requirements. Reverse, for example, must be able to decrement its arguments as well as increment them; it uses the expression –last. In terms of concepts, we say that reverse‘s arguments must be models of Bidirectional Iterator rather than Input Iterator. Input Iterator事实上是一个非常弱的概念：它强加了很少的要求。一个Input Iterator必须提供一个指针算术的子集（它必须可以去通过前缀或者后缀的++递增一个Input Iterator），但是不需要提供所以的指针运算。这些对于find来说已经足够了，但是其他的一些算法需要一些额外的要求。例如Reverse必须可以通过–实现递减。按照概念的说法，我们说Reverse的参数为Bidirectional Iterator模型而非Input Iterator。 The Bidirectional Iterator concept is very similar to the Input Iterator concept: it simply imposes some additional requirements. The types that are models of Bidirectional Iterator are a subset of the types that are models of Input Iterator: every type that is a model of Bidirectional Iterator is also a model of Input Iterator. Int*, for example, is both a model of Bidirectional Iterator and a model of Input Iterator, but istream_iterator, is only a model of Input Iterator: it does not conform to the more stringent Bidirectional Iterator requirements. Bidirectional Iterator的概念和Input Iterator非常相似: 它仅仅加了一些额外的要求。Bidirectional Iterator的模型也是一个Input Iterator的子集: 任何Bidirectional Iterator 的模型同时也是一个Input Iterator 的模型。 例如, Int*,既是 Bidirectional Iterator 的模型也是一个Input Iterator 的模型, 但是istream_iterator仅仅是一个的模型Input Iterator: 它并没有符合Bidirectional Iterator更严格的要求。 We describe the relationship between Input Iterator and Bidirectional Iterator by saying that Bidirectional Iterator is a refinement of Input Iterator. Refinement of concepts is very much like inheritance of C++ classes; the main reason we use a different word, instead of just calling it “inheritance”, is to emphasize that refinement applies to concepts rather than to actual types. 我们描述Input Iterator和Bidirectional Iterator的关系时说Bidirectional Iterator是一个更精巧的InputIterator。精巧概念非常像C++类的派生，我们用一个不同的词的主要原因是强调精巧是应用与概念而不是实际的类型。 There are actually three more iterator concepts in addition to the two that we have already discussed: the five iterator concepts are Output Iterator, Input Iterator, Forward Iterator, Bidirectional Iterator, and Random Access Iterator; Forward Iterator is a refinement of Input Iterator, Bidirectional Iterator is a refinement of Forward Iterator, and Random Access Iterator is a refinement of Bidirectional Iterator. (Output Iterator is related to the other four concepts, but it is not part of the hierarchy of refinement: it is not a refinement of any of the other iterator concepts, and none of the other iterator concepts are refinements of it.) The Iterator Overview has more information about iterators in general. 除了我们已经讨论的两个外实际上还要更多的迭代器类型：五种迭代器类型分别为Output Iterator, Input Iterator, Forward Iterator, Bidirectional Iterator和Random Access Iterator; Forward Iterator 是一个精巧的Input Itearot, Bidirectional Iterator是一个更精巧的 Forward Iterator, Random Access Iterator 是一个更精巧的Bidirectional Iterator. (Output Iterator 和其他四中迭代器相关，但不是派生和精巧关系) Iterator Overview 有更多的关于iterators的一般信息. Container classes, like iterators, are organized into a hierarchy of concepts. All containers are models of the concept Container; more refined concepts, such as Sequence and Associative Container, describe specific types of containers.

容器类，像迭代器一样被组织进一个概念中。所以的容器都是概念Container的模型；更加精巧的概念，比如说Sequence and Associative Container, 描述了更特别的容器。

##

下面这部分暂时不翻译，以后看需要时在看。

Other parts of the STL

If you understand algorithms, iterators, and containers, then you understand almost everything there is to know about the STL. The STL does, however, include several other types of components. First, the STL includes several utilities: very basic concepts and functions that are used in many different parts of the library. The concept Assignable, for example, describes types that have assignment operators and copy constructors; almost all STL classes are models of Assignable, and almost all STL algorithms require their arguments to be models of Assignable. Second, the STL includes some low-level mechanisms for allocating and deallocating memory. Allocators are very specialized, and you can safely ignore them for almost all purposes.

Finally, the STL includes a large collection of function objects, also known as functors. Just as iterators are a generalization of pointers, function objects are a generalization of functions: a function object is anything that you can call using the ordinary function call syntax. There are several different concepts relating to function objects, including Unary Function (a function object that takes a single argument, i.e. one that is called as f(x)) and Binary Function (a function object that takes two arguments, i.e. one that is called as f(x, y)). Function objects are an important part of generic programming because they allow abstraction not only over the types of objects, but also over the operations that are being performed.