STL学习

侯捷STL学习(一)

• 开始跟着《STL源码剖析》的作者侯捷真人视频，学习STL,了解STL背后的真实故事！
• 视频链接：侯捷STL
• 还有很大其他视频需要的留言

第一节：STL版本和重要资源

• STL和标准库的区别

• 三个网站
  • CPlusPlus
  • CppReference
  • gcc.gnu.org
  • Boost

第二节：STL六大部件

• 迭代器将容器和算法结合起来
• 分配器实现，适配器用的地方很多

• 实例：

• 理解容器的前闭后开的设计。迭代器类似于指针，很多操作和指针差不多++,--运算。vec.begin(),vec.end()指向容器最后一个元素的下一个位置，解引用*（vec.end()）错误！
• auto关键字的应用

std::vector<double> vec;
for(auto elem: vec)
{
   std::cout<<elem<<std::endl;
}

第三节：容器之分类和各种测试（一）

分类结构

• 红色框中标注的是C++11开始有的容器
• Array数组容器，大小固定的
• Deque:两段都可以进行插入删除操作，但是从内存上讲不通，怎么实现的要从后面的学习知道。
• List:是一个双向的循环链表，注意是双向的。
• Forward-List:单向链表，当能用单向链表的时候尽量用，可以减少内存空间，一个指针在32位pc上占4个字节，当数据量很多上百万，不可忽略！
• Set键值都一样，MultiSet允许元素有重复。
• Set/Map用红黑树实现，RB-tree是自平衡的二叉树。
• Unorder Containers:是C++标准库里卖的内容。
• 根据这些图例，可以知道这些容器在内存用到的数据结构是什么样的。
• HashTable实现方法很多，但基本都用Separate Chaining(分离链地址法实现)。

测试Array

• 指针void* a -> *(long*)a;
• array<long, size> c使用初始化大小，#include<array>
• c.data()返回这个数组的初始地址，和数组的地址对比
• qsort应用：qsort(c.data,size,size(long),comparelongs)
• bsearch()应用,查找前必须排好序了：bsearch(&target,(c.data()),size,size(long),comparelongs)
• qsort,bsearch包含头文件#include<cstdlib>，C本身库函数

#include <array>
#include <iostream>
#include <ctime> 
#include <cstdlib> //qsort, bsearch, NULL

namespace jj01
{
void test_array()
{
    cout << "
test_array().......... 
";
     
array<long,ASIZE> c;    
            
clock_t timeStart = clock();                                    
    for(long i=0; i< ASIZE; ++i) {
        c[i] = rand(); 
    }
    cout << "milli-seconds : " << (clock()-timeStart) << endl;  //
    cout << "array.size()= " << c.size() << endl;       
    cout << "array.front()= " << c.front() << endl; 
    cout << "array.back()= " << c.back() << endl;   
    cout << "array.data()= " << c.data() << endl;   
    
long target = get_a_target_long();

    timeStart = clock();
    ::qsort(c.data(), ASIZE, sizeof(long), compareLongs);
long* pItem = (long*)::bsearch(&target, (c.data()), ASIZE, sizeof(long), compareLongs); 
    cout << "qsort()+bsearch(), milli-seconds : " << (clock()-timeStart) << endl;   //    
    if (pItem != NULL)
        cout << "found, " << *pItem << endl;
    else
        cout << "not found! " << endl;  
}
}

第四节：容器之分类和各种测试（二）

测试Vector

• 主要通过程序细节说明
• namespace命名空间的说明
• vector的增长速度是2倍增长，当capacity不够时，容量增长为前面的2倍。是在另外的2倍空间！
• try...catch...捕获函数，字符串最大占一个指针大小，空间不够的时候抛出，abort()退出
• ::find()模板函数，加冒号表明是全局函数，当没有冒号时，编译器在当前没有找到，也会到全局去找。
• 用两种查找算法比较，find()用时更少。

#include <vector>
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()   //qsort, bsearch, NULL
#include <cstdio>  //snprintf()
#include <iostream>
#include <ctime> 
#include <algorithm>    //sort()
namespace jj02
{
void test_vector(long& value)
{
    cout << "
test_vector().......... 
";
     
vector<string> c;   
char buf[10];
            
clock_t timeStart = clock();                                
    for(long i=0; i< value; ++i)
    {
        try {
            snprintf(buf, 10, "%d", rand());
            c.push_back(string(buf));           
        }
        catch(exception& p) {
            cout << "i=" << i << " " << p.what() << endl;   
                 //曾經最高 i=58389486 then std::bad_alloc
            abort();
        }
    }
    cout << "milli-seconds : " << (clock()-timeStart) << endl;  
    cout << "vector.max_size()= " << c.max_size() << endl;  //1073747823
    cout << "vector.size()= " << c.size() << endl;      
    cout << "vector.front()= " << c.front() << endl;    
    cout << "vector.back()= " << c.back() << endl;  
    cout << "vector.data()= " << c.data() << endl;
    cout << "vector.capacity()= " << c.capacity() << endl << endl;      

                                                                                
string target = get_a_target_string();
    {
    timeStart = clock();
auto pItem = find(c.begin(), c.end(), target);
    cout << "std::find(), milli-seconds : " << (clock()-timeStart) << endl;  
     
    if (pItem != c.end())
        cout << "found, " << *pItem << endl << endl;
    else
        cout << "not found! " << endl << endl;
    }

    {
    timeStart = clock();
    sort(c.begin(), c.end());
    cout << "sort(), milli-seconds : " << (clock()-timeStart) << endl; 
    
    timeStart = clock();        
string* pItem = (string*)::bsearch(&target, (c.data()), 
                                   c.size(), sizeof(string), compareStrings); 
    cout << "bsearch(), milli-seconds : " << (clock()-timeStart) << endl; 
       
    if (pItem != NULL)
        cout << "found, " << *pItem << endl << endl;
    else
        cout << "not found! " << endl << endl;  
    }
    
    c.clear();
    test_moveable(vector<MyString>(),vector<MyStrNoMove>(), value); 
}   
}

第五节：容器之分类和各种测试（三）

测试List，双向链表

• list.max_size()按理list是动态申请空间的，为什么最大的size呢？
• list双向链表实现
• 有趣的c.sort(),这里注意在STL标准库全局有一个sort函数，但这里调用的是list容器自身内部的sort函数。注意在STL容器中有些自身有sort函数，此时用自身的排序算法更快。

#include <list>
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()
#include <cstdio>  //snprintf()
#include <algorithm> //find()
#include <iostream>
#include <ctime> 
namespace jj03
{
void test_list(long& value)
{
    cout << "
test_list().......... 
";
     
list<string> c;     
char buf[10];
            
clock_t timeStart = clock();                            
    for(long i=0; i< value; ++i)
    {
        try {
            snprintf(buf, 10, "%d", rand());
            c.push_back(string(buf));       
        }
        catch(exception& p) {
            cout << "i=" << i << " " << p.what() << endl;   
            abort();
        }
    }
    cout << "milli-seconds : " << (clock()-timeStart) << endl;      
    cout << "list.size()= " << c.size() << endl;
    cout << "list.max_size()= " << c.max_size() << endl;    //357913941
    cout << "list.front()= " << c.front() << endl;  
    cout << "list.back()= " << c.back() << endl;        
        
string target = get_a_target_string();      
    timeStart = clock();        
auto pItem = find(c.begin(), c.end(), target);                      
    cout << "std::find(), milli-seconds : " << (clock()-timeStart) << endl;     
    
    if (pItem != c.end())
        cout << "found, " << *pItem << endl;
    else
        cout << "not found! " << endl;  
        
    timeStart = clock();        
    c.sort();                       
    cout << "c.sort(), milli-seconds : " << (clock()-timeStart) << endl;                
        
    c.clear();
    test_moveable(list<MyString>(),list<MyStrNoMove>(), value);                             
}   
}

测试forward-list，单向链表

• forward-list单向链表，C++11出现的
• push_front在链表头插入，不提供在尾部插入，效率低些。
• front取链表头的元素，不提供back()操作取链表尾的元素。
• c.sort()用它自身的排序算法

#include <forward_list>
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()
#include <cstdio>  //snprintf()
#include <iostream>
#include <ctime> 
namespace jj04
{
void test_forward_list(long& value)
{
    cout << "
test_forward_list().......... 
";
     
forward_list<string> c;     
char buf[10];
            
clock_t timeStart = clock();                                
    for(long i=0; i< value; ++i)
    {
        try {
            snprintf(buf, 10, "%d", rand());
            c.push_front(string(buf));                      
        }
        catch(exception& p) {
            cout << "i=" << i << " " << p.what() << endl;   
            abort();
        }
    }
    cout << "milli-seconds : " << (clock()-timeStart) << endl;  
    cout << "forward_list.max_size()= " << c.max_size() << endl;  //536870911
    cout << "forward_list.front()= " << c.front() << endl;  


string target = get_a_target_string();  
    timeStart = clock();            
auto pItem = find(c.begin(), c.end(), target);  
    cout << "std::find(), milli-seconds : " << (clock()-timeStart) << endl;     
    
    if (pItem != c.end())
        cout << "found, " << *pItem << endl;
    else
        cout << "not found! " << endl;  
        
    timeStart = clock();        
    c.sort();                       
    cout << "c.sort(), milli-seconds : " << (clock()-timeStart) << endl;        
    
    c.clear();   
}                                            
}

测试slist

• Gnu C之前的单链表,forward-list是C++11才出现的
• #include<extslist>头文件

#include <extslist>
    //注意, 上一行並沒有引發警告訊息如 #include <exthash_set> 所引發者： 
    //...4.9.2includec++ackwardackward_warning.h 
    //[Warning] ...
    
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()
#include <cstdio>  //snprintf()
#include <iostream>
#include <ctime> 
namespace jj10
{
void test_slist(long& value)
{
    cout << "
test_slist().......... 
";
     
    __gnu_cxx::slist<string> c;     
    char buf[10];
            
    clock_t timeStart = clock();                                
    for(long i=0; i< value; ++i)
    {
        try {
            snprintf(buf, 10, "%d", rand());
            c.push_front(string(buf));          
        }
        catch(exception& p) {
            cout << "i=" << i << " " << p.what() << endl;   
            abort();
        }
    }
    cout << "milli-seconds : " << (clock()-timeStart) << endl;          
}                                                           
}

测试deque

• 双向开口，是分段连续，感觉是连续的，其实不是。
• 内存上两边都可以扩充
• 每次512扩充，两边扩充申请buffer,buffer由指针指向
• max_size由限制，使用全局的sort排序

#include <deque>
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()
#include <cstdio>  //snprintf()
#include <iostream>
#include <ctime> 
namespace jj05
{
void test_deque(long& value)
{
    cout << "
test_deque().......... 
";
     
deque<string> c;    
char buf[10];
            
clock_t timeStart = clock();                                
    for(long i=0; i< value; ++i)
    {
        try {
            snprintf(buf, 10, "%d", rand());
            c.push_back(string(buf));                       
        }
        catch(exception& p) {
            cout << "i=" << i << " " << p.what() << endl;   
            abort();
        }
    }
    cout << "milli-seconds : " << (clock()-timeStart) << endl;      
    cout << "deque.size()= " << c.size() << endl;
    cout << "deque.front()= " << c.front() << endl; 
    cout << "deque.back()= " << c.back() << endl;   
    cout << "deque.max_size()= " << c.max_size() << endl;   //1073741821    
    
string target = get_a_target_string();  
    timeStart = clock();            
auto pItem = find(c.begin(), c.end(), target);  
    cout << "std::find(), milli-seconds : " << (clock()-timeStart) << endl; 
    
    if (pItem != c.end())
        cout << "found, " << *pItem << endl;
    else
        cout << "not found! " << endl;  
        
    timeStart = clock();        
    sort(c.begin(), c.end());                       
    cout << "sort(), milli-seconds : " << (clock()-timeStart) << endl;      
    
    c.clear();
    test_moveable(deque<MyString>(),deque<MyStrNoMove>(), value);                               
}                                                           
}

测试stack

• 栈,数据结构上和deque差不多
• 两段插入插入删除受限的容器
• 也有人叫做容器的适配器adapter
• 没有提供容器的迭代器iterator,否则对迭代器的操作会破坏堆栈的结构
• 也没有提供find,sort的功能；但是有时候让你实现堆栈的排序操作

#include <stack>
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()
#include <cstdio>  //snprintf()
#include <iostream>
#include <ctime> 
namespace jj17
{
void test_stack(long& value)
{
    cout << "
test_stack().......... 
";
     
stack<string> c;    
char buf[10];
            
clock_t timeStart = clock();                                
    for(long i=0; i< value; ++i)
    {
        try {
            snprintf(buf, 10, "%d", rand());
            c.push(string(buf));                        
        }
        catch(exception& p) {
            cout << "i=" << i << " " << p.what() << endl;
            abort();
        }
    }
    cout << "milli-seconds : " << (clock()-timeStart) << endl;  
    cout << "stack.size()= " << c.size() << endl;
    cout << "stack.top()= " << c.top() << endl; 
    c.pop();
    cout << "stack.size()= " << c.size() << endl;
    cout << "stack.top()= " << c.top() << endl; 
    
    
    {
stack<string, list<string>> c;      //以 list 為底層 
    for(long i=0; i< 10; ++i) {
            snprintf(buf, 10, "%d", rand());
            c.push(string(buf));                        
    }
    cout << "stack.size()= " << c.size() << endl;
    cout << "stack.top()= " << c.top() << endl; 
    c.pop();
    cout << "stack.size()= " << c.size() << endl;
    cout << "stack.top()= " << c.top() << endl; 
    }   
    
    {
stack<string, vector<string>> c;    //以 vector 為底層 
    for(long i=0; i< 10; ++i) {
            snprintf(buf, 10, "%d", rand());
            c.push(string(buf));                        
    }
    cout << "stack.size()= " << c.size() << endl;
    cout << "stack.top()= " << c.top() << endl; 
    c.pop();
    cout << "stack.size()= " << c.size() << endl;
    cout << "stack.top()= " << c.top() << endl; 
    }

    {
stack<string, set<string>> c;   //以 set 為底層 
/*!
    for(long i=0; i< 10; ++i) {
            snprintf(buf, 10, "%d", rand());
            c.push(string(buf));                        
    }
    cout << "stack.size()= " << c.size() << endl;
    cout << "stack.top()= " << c.top() << endl; 
    c.pop();
    cout << "stack.size()= " << c.size() << endl;
    cout << "stack.top()= " << c.top() << endl; 
    
//[Error] 'class std::set<std::basic_string<char> >' has no member named 'push_back'
//[Error] 'class std::set<std::basic_string<char> >' has no member named 'back'
//[Error] 'class std::set<std::basic_string<char> >' has no member named 'pop_back'
*/
    }
            
//!stack<string, map(string>> c5;   ////以 map 為底層, [Error] template argument 2 is invalid
//!stack<string>::iterator ite1;    //[Error] 'iterator' is not a member of 'std::stack<std::basic_string<char> >'
        
}                                                           
}

测试queue

• 堆，数据结构上有deque衍生出来的
• 没有提供容器的迭代器iterator,否则对迭代器的操作会破坏堆栈的结构

#include <queue>
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()
#include <cstdio>  //snprintf()
#include <iostream>
#include <ctime> 
namespace jj18
{
void test_queue(long& value)
{
    cout << "
test_queue().......... 
";
     
queue<string> c;    
char buf[10];
            
clock_t timeStart = clock();                                
    for(long i=0; i< value; ++i)
    {
        try {
            snprintf(buf, 10, "%d", rand());
            c.push(string(buf));                        
        }
        catch(exception& p) {
            cout << "i=" << i << " " << p.what() << endl;
            abort();
        }
    }
    cout << "milli-seconds : " << (clock()-timeStart) << endl;  
    cout << "queue.size()= " << c.size() << endl;
    cout << "queue.front()= " << c.front() << endl; 
    cout << "queue.back()= " << c.back() << endl;       
    c.pop();
    cout << "queue.size()= " << c.size() << endl;
    cout << "queue.front()= " << c.front() << endl; 
    cout << "queue.back()= " << c.back() << endl;   
    
    
    {
queue<string, list<string>> c;      //以 list 為底層 
    for(long i=0; i< 10; ++i) {
            snprintf(buf, 10, "%d", rand());
            c.push(string(buf));                        
    }
    cout << "queue.size()= " << c.size() << endl;
    cout << "queue.front()= " << c.front() << endl; 
    cout << "queue.back()= " << c.back() << endl;       
    c.pop();
    cout << "queue.size()= " << c.size() << endl;
    cout << "queue.front()= " << c.front() << endl; 
    cout << "queue.back()= " << c.back() << endl;   
    }   
    
    {
queue<string, vector<string>> c;    //以 vector 為底層 
    for(long i=0; i< 10; ++i) {
            snprintf(buf, 10, "%d", rand());
            c.push(string(buf));                        
    }
    cout << "queue.size()= " << c.size() << endl;
    cout << "queue.front()= " << c.front() << endl; 
    cout << "queue.back()= " << c.back() << endl;       
    //!c.pop();  //[Error] 'class std::vector<std::basic_string<char> >' has no member named 'pop_front'
    cout << "queue.size()= " << c.size() << endl;
    cout << "queue.front()= " << c.front() << endl; 
    cout << "queue.back()= " << c.back() << endl;   
    }   

    {
queue<string, set<string>> c;       //以 set 為底層 
/*!
    for(long i=0; i< 10; ++i) {
            snprintf(buf, 10, "%d", rand());
            c.push(string(buf));                        
    }
    cout << "queue.size()= " << c.size() << endl;
    cout << "queue.front()= " << c.front() << endl; 
    cout << "queue.back()= " << c.back() << endl;       
    c.pop();
    cout << "queue.size()= " << c.size() << endl;
    cout << "queue.front()= " << c.front() << endl; 
    cout << "queue.back()= " << c.back() << endl;
//[Error] 'class std::set<std::basic_string<char> >' has no member named 'push_back'
//[Error] 'class std::set<std::basic_string<char> >' has no member named 'front'
//[Error] 'class std::set<std::basic_string<char> >' has no member named 'pop_front'
*/      
    }
    
//! queue<string, map<string>> c5;  //以 map 為底層, [Error] template argument 2 is invalid
//! queue<string>::iterator ite1;   //[Error] 'iterator' is not a member of 'std::queue<std::basic_string<char> >'  
}                                                           
}

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