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STL概述

STL是Standard Template Library的缩写，是C++标准库中最强大、最复杂、最有用的部分。STL主要由容器（container）、跌代子（iterator）、算法（algorithm）所组成。还有仿函数（functor）、适配器（adapter）、配置器（allocator）等辅助组件。

1. 容器container

容器是存放和管理数据元素的数据结构，分为两大类：顺序容器（sequence container）和关联容器（associative container）。

除此以外还有：

容器一般使用模板类来实现

2. 跌代子iterator

跌代子是用来访问容器内元素的对象，类似指针。 跌代子根据能力的不同，分为：

另外还有

3. 算法algorithm

算法是用来处理容器内的元素的一些操作，比如搜索、排序、拷贝、修改等。算法一般使用函数模板来实现。

4. 仿函数functor

用法类似函数的对象。用重载了operator()的类或者模板类来实现

容器与容器适配器

1. vector向量

1.1. 接口说明

vector的用法类似于数组，不同的是数组空间可以动态分配。 

   1 #include <vector>
   2 namespace std {
   3    template< class T, class Allocator = allocator<T> > vector;
   4 }

T可以是任何类型，但是必须满足：assignable, copyable

1.1.1. 构造方法

   1 vector< int > a2(10); //构造10个元素的vector
   2 vector< int > a3(10, 5); //构造一个10个元素的vector，每个元素都是5
   3 vector< int > a4(a2); //构造一个vector与a2完全一样
   4 vector< int > a1; // 构造一个空的vector
   5 int values[] = {10, 11, 12, 13, 14};
   6 vector< int > a5( values, values+5); //通过迭代子来构造vector
   7

1.1.2. 不变操作和赋值

   1 a1.size( ) //取容器内元素的个数
   2 a1.empty( ) //判断容器是否为空
   3 a1 == a2 //判断两个容器的内容是否相同, 还有!=, <, >, <=, >=
   4 a1 = a2 //将a2全部元素赋给a1
   5 a1.assign( values, values+5 ) //将values[0]到values[4]赋给a1
   6 a1.assign( 10, 5) //给a1赋值10个5
   7

1.1.3. 元素访问

   1 a1[ 5 ] //取第5个元素，下标从0开始
   2 a1.at(5) //取第5个元素，带边界检查
   3 a1.front() //取第0个元素
   4 a1.end() //取最后一个元素
   5

1.1.4. 跌代子

   1 a1.begin() //随机跌代子，指向a1[0]
   2 a1.end()  //随机跌代子，指向最后一个的下一个
   3 a1.rbegin() //随机跌代子，指向最后一个
   4 a1.rend() //随机跌代子，指向a1[0]的前一个
   5

1.1.5. 插入删除操作

   1 a1.insert( a1.begin(), 5); //在a1的最前面插入一个5
   2 a1.insert(a1.end(), 10, 6); //在a1的最后面插入10个6
   3 a1.insert(a1.begin(), values, values+5) //在a1的最前面插入values[0]到values[4]
   4 a1.push_back( 5 ) //在a1的最后面插入一个5
   5 a1.pop_back( ) // 删除a1的最后一个元素
   6 a1.erase( a1.begin() ) //删除a1中的第一个元素
   7 a1.erase( a1.begin(), a1.begin() +2) //删除a1最前面2个元素
   8 a1.resize( 10 ) //将a1元素个数改为10，增加的部分值为默认构造
   9 a1.resize( 10, 6) //将a1元素个数改为10，增加的部分值为6
  10 a1.clear() //清除所有元素
  11

1.2. 用法实例

   1 #include <vector>
   2 int main() {
   3    using namespace std;
   4    vector< string > sentence;
   5    sentence.reserve( 5 );
   6    sentence.push_back( “ Hello, “);
   7    sentence.push_back( “how “);
   8    sentence.push_back( “are “);
   9    sentence.push_back( "you ");
  10    sentence.push_back( “?“);
  11    copy( sentence.begin(), sentence.end(), ostream_iterator<string>(cout, “  “));
  12    cout << endl;
  13    cout << sentence.size() << endl;
  14    cout << sentence.capacity() << endl;
  15    swap( sentence[1], sentence[3]);
  16    sentence.insert( find(sentence.begin(), sentence.end(), “?”), “always”);
  17    sentence.back() = “!”;
  18    copy( sentence.rbegin(), sentence.rend(), ostream_iterator<string>(cout, “  “));
  19    cout << endl;
  20 }

用vector代替数组使用 

   1 vector < int > a(10); // int a[10];
   2 a[0] = 1;
   3 a[1] = 2;
   4 a[2] = a[0] + a[1];
   5 for( int i = 0; i < a.size(); i++)
   6    scanf( “%d”, &a[i] );

1.3. vector的实现

vector的实现类似于数据结构中的顺序表

attachment:vector.jpg 

   1 template<class T, class Alloc=alloc>
   2 class vector {
   3 public:
   4     typedef T value_type;
   5     typedef value_type* iterator;
   6     typedef value_type& reference;
   7     typedef size_t size_type;
   8 protected:
   9     iterator start;
  10     iterator finish;
  11     iterator end_of_storage;
  12 
  13 
  14 public:
  15     iterator begin() { return start; }
  16     iterator end() { return finish; }
  17     size_type size() const { //返回当前元素个数
  18         return size_type(end() - begin());
  19     }
  20     bool empty() const {
  21         return begin() == end();
  22     }
  23     reference operator[](size_type n) {
  24         return *(begin() + n);
  25     }
  26     reference front() {
  27         return *begin();
  28     }
  29     reference back() {
  30         return *(end() - 1);
  31     }
  32     size_type capacity() const {  //返回当前容量的大小
  33         return size_type(end_of_storage - begin()); 
  34     } 
  35     size_type reserve(size_type n); //改变容量的大小
  36     void push_back(const T& x) {
  37         if(finish != end_of_storage) {
  38             construct(finish, x);
  39             ++finish;
  40         } else {
  41             insert_aux(end(), x);
  42         }
  43     }
  44 protected:
  45     typedef simple_alloc<value_type, Alloc> data_allocator;
  46     void deallocate() {
  47         if(start) data_allocator::deallocate(start, end_of_storage - start);
  48     }
  49     
  50     void insert_aux(iterator position, const T& x) {
  51         if(finish != end_of_storage) {
  52             construct(finish, *(finish-1));
  53             ++finish;
  54             T x_copy = x;
  55             copy_backward(position, finish-2, finish-1);
  56             *position = x_copy;
  57         } else {
  58             const size_type old_size = size();
  59             const size_type len = old_size != 0 ? 2 * old_size : 1;
  60             iterator new_start = data_allocator::alloate(len);
  61             iterator new_finish = new_start;
  62             try {
  63                 new_finish = uninitialized_copy(start, position, new_start);
  64                 construct(new_finish, x);
  65                 ++ new_finish;
  66                 new_finish = uninitialized_copy(position, finish, new_finish);
  67             } catch(...) {
  68                 destroy(new_start, new_finish);
  69                 data_allocator::deallocate(new_start, len);
  70                 throw;
  71             }
  72             destroy(begin(), end());
  73             deallocate();
  74             start = new_start;
  75             finish = new_finish;
  76             end_of_storage = new_start + len;
  77         }
  78     }
  79 };

2. deque双端队列

deque与vector相似，区别是deque两端都是开放的，两端插入删除都很快。在头文件<deque>中定义。 attachment:deque.jpg

实现： attachment:deque_imp.jpg

可以随机访问，但速度比vector稍慢

迭代子是随机跌代子，是一种class而不是原始指针

操作非常相似，增加操作：push_front, pop_front，减少操作：reserve,capacity

任何插入和删除操作都可能使跌代子失效

例子：

例子： 

   1 int main() {
   2     deque<string> coll;
   3     coll.assign (3, string("string"));
   4     coll.push_back ("last string");
   5     coll.push_front ("first string");
   6     copy (coll.begin(), coll.end(), ostream_iterator<string>(cout,"\n"));
   7     coll.pop_front();
   8     coll.pop_back();
   9     for (int i=1; i<coll.size(); ++i) {
  10         coll[i] = "another " + coll [i];
  11     }
  12     coll.resize (4, "resized string");
  13     copy (coll.begin(), coll.end(), ostream_iterator<string>(cout,"\n"));
  14 }

3. list链表

一般为双链表实现

#include <list> 提供双向跌代子，不能随机访问 插入删除操作非常快速 插入删除操作不会使跌代子失效 提供了一些移动元素的算法，比通用算法更快 

   1 c1.swap(c2)：交换两个链表的内容
   2 c.remove(val)
   3 c.remove_if(predictor)
   4 c.unique() 删除重复元素
   5 c.splice() 将一个链表中的元素切一部分到另一个链表
   6 c.sort() 排序
   7 c.merge() 合并两个链表
   8 c.reverse() 倒置

例 

   1 void printLists (const list<int>& 11, const list<int>& 12) {
   2 cout << "list1: ";
   3 copy (l1.begin(), l1.end(), ostream_iterator<int>(cout," "));
   4 cout << endl << "list2: ";
   5 copy (12.begin(), 12.end(), ostream_iterator<int>(cout," "));
   6 cout << endl << endl;
   7 }
   8 int main() {
   9 list<int> list1, list2;
  10 for (int i=0; i<6; ++i) {
  11 list1.push_back(i);
  12 list2.push_front(i);
  13 }
  14 printLists(list1, list2);
  15 list2.splice(find(list2.begin(),list2.end(), 3), list1); 
  16 printLists(list1, list2);
  17 list2.splice(list2.end(), list2, list2.begin());
  18 printLists(list1, list2);
  19 list2.sort();
  20 list1 = list2;
  21 list2.unique();
  22 printLists(list1, list2);
  23 list1.merge(list2);
  24 printLists(list1, list2);
  25 }

4. stack栈

#include <stack> namespace std { template <class T, class Container = deque<T> > class stack; } 实现：

主要操作 push() 入栈 top() 取栈顶元素 pop() 出栈 例： 

   1 int main() {
   2 stack<int> st;
   3 st.push(l);
   4 st.push(2);
   5 st.push(3);
   6 cout << st.top() << ' ';
   7 st.pop() ;
   8 cout << st.top() << ' ';
   9 st.pop() ;
  10 st.top() = 77;
  11 st.push(4);
  12 st.push(5);
  13 st.pop() ;
  14 while (!st.empty()) {
  15 cout << st.top() << ' ';
  16 st.pop() ;
  17 }
  18 cout << endl;
  19 }

5. queue队列

#include <queue> namespace std { template <class T, class Container = deque<T> > class queue; } 实现

主要操作： push pop back front

例 

   1 int main() {
   2 queue<string> q;
   3 q.push("These ");
   4 q.push("are ");
   5 q.push("more than ");
   6 cout << q.front();
   7 q.pop();
   8 cout << q.front();
   9 q.pop();
  10 q.push(''four ");
  11 q.push("words!");
  12 q.pop();
  13 cout << q.front();
  14 q.pop();
  15 cout << q.front() << endl;
  16 q.pop();
  17 cout << "number of elements in the queue: " << q.size() << endl;
  18 }

6. priority_queue优先队列

按照大小顺序出队的队列 #include <queue> namespace std { template <class T, class Container = vector<T>, class Compare = less<typename Container::value_type> > class priority_queue; } 实现：堆

push() 入队 top() 读取下一个元素 pop() 删除下一个元素 

   1 int main() {
   2 priority_queue<float> q;
   3 q.push(66.6);
   4 q.push(22.2);
   5 q.push(44.4);
   6 cout << q.top() << ' ';
   7 q.pop();
   8 cout << q.top() << endl;
   9 q.pop();
  10 q.push(11.1);
  11 q.push(55.5);
  12 q.push(33.3);
  13 q.pop();
  14 while (!q.empty()) {
  15 cout << q.top() << ' ';
  16 q.pop();
  17 }
  18 cout << endl;
  19 }

7. set与multi_set

在这两种容器中，元素能够根据指定的排序规则自动的排序，以优化查找。两者区别是：set不允许有重复的元素，multi_set允许有重复的元素。 

   1 #include <set>
   2 namespace std {
   3 template <class T,
   4 class Compare = less<T>,
   5 class Allocator = allocator<T> >
   6 class set;
   7 template <class T,
   8 class Compare = less<T>,
   9 class Allocator = allocator<T> >
  10 class multiset;
  11 }

内部结构

例子： 

   1 #include <iostream>
   2 #include <set>
   3 using namespace std;
   4 int main() {
   5 typedef set<int,greater<int> > IntSet;
   6 IntSet coll1; // empty set container
   7 coll1.insert(4);
   8 coll1.insert(3);
   9 coll1.insert(5);
  10 coll1.insert(1);
  11 coll1.insert(6);
  12 coll1.insert(2);
  13 coll1.insert(5);
  14 IntSet::iterator pos;
  15 for (pos = coll1.begin(); pos != coll1.end(); ++pos) {
  16 cout << *pos << ' ';
  17 }
  18 cout << endl;
  19 pair<IntSet::iterator,bool> status = coll1.insert(4);
  20 if (status.second) {
  21 cout << "4 inserted as element "<< distance (coll1.begin(),status. first) + 1<< endl;
  22 }else {
  23 cout << "4 already exists" << endl;
  24 }
  25 set<int> coll2(coll1.begin(),
  26 coll1.end());
  27 copy (coll2.begin(), coll2.end(), ostream_iterator<int>(cout," "));
  28 cout << endl;
  29 coll2.erase (coll2.begin(), coll2.find(3));
  30 int num;
  31 num = coll2.erase (5);
  32 cout << num << " element(s) removed" << endl;
  33 copy (coll2.begin(), coll2.end(), ostream_iterator<int>(cout," "));
  34 cout << endl;
  35 }

8. map与multi_map

存放关键字与对应值的数据结构 

   1 #include <map>
   2 namespace std {
   3 template <class Key, class T,
   4 class Compare = less<Key>,
   5 class Allocator = allocator<pair<const Key,T> > >
   6 class map;
   7 template <class Key, class T,
   8 class Compare = less<Key>,
   9 class Allocator = allocator<pair<const Key,T> > >
  10 class multimap;
  11 }

内部结构 

   1 #include <iostream>
   2 #include <map>
   3 #include <string>
   4 using namespace std;
   5 int main() {
   6 typedef map<string,float> StringFloatMap;
   7 StringFloatMap stocks; // create empty container
   8 stocks["BASF"] = 369.50;
   9 stocks["VW"] = 413.50;
  10 stocks["Daimler"] = 819.00;
  11 stocks["BMW"] = 834.00;
  12 stocks["Siemens"] = 842.20;
  13 StringFloatMap::iterator pos;
  14 for (pos = stocks.begin(); pos != stocks.end(); ++pos) {
  15 cout << "stock: " << pos->first << "\t" << "price: " << pos->second << endl;
  16 }
  17 cout << endl;
  18 for (pos = stocks.begin(); pos != stocks.end(); ++pos) {
  19 pos->second *= 2;
  20 }
  21 for (pos = stocks.begin(); pos != stocks.end(); ++pos) {
  22 cout << "stock: " << pos->first << "\t"<< "price: " << pos->second << endl;
  23 }
  24 cout << endl;
  25 stocks["Volkswagen"] = stocks["VW"];
  26 stocks.erase("VW");
  27 for (pos = stocks.begin(); pos != stocks.end(); ++pos) {
  28 cout << "stock: " << pos->first << "\t"<< "price: " << pos->second << endl;
  29 }
  30 }

练习

  1. Write a program to print a histogram of the frequencies of different characters in its input.
  2. Write a program to print a histogram of the lengths of words in its input. It is easy to draw the histogram with the bars horizontal; a vertical orientation is more challenging.
  3. Write a program that prints the distinct words in its input sorted into decreasing order of frequency of occurrence. Precede each word by its count.
  4. Write a cross-referencer that prints a list of all words in a document, and for each word, a list of the line numbers on which it occurs.

  5. Write the program tail, which prints the last n lines of its input. By default, n is set to 10, let us say, but it can be changed by an optional argument so that

    tail -n
    prints the last n lines. The program should behave rationally no matter how unreasonable the input or the value of n. Write the program so it makes the best use of available storage.
  6. Write a program to remove all comments from a C program. Don't forget to handle quoted strings and character constants properly. C comments don't nest.
  7. Write a program to check a C program for rudimentary syntax errors like unmatched parentheses, brackets and braces. Don't forget about quotes, both single and double, escape sequences, and comments. (This program is hard if you do it in full generality.)
  8. Write a program to implement a queue using two stacks.
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