STL标准库与泛型编程（侯捷）笔记1

STL标准库与泛型编程（侯捷）

本文是学习笔记，仅供个人学习使用。如有侵权，请联系删除。

参考链接

Youbute: 侯捷-STL标准库与泛型编程

B站: 侯捷 - STL

Github:STL源码剖析中源码 https://github.com/SilverMaple/STLSourceCodeNote/tree/master

Github:课程ppt和源码 https://github.com/ZachL1/Bilibili-plus

文章目录

  • STL标准库与泛型编程（侯捷）
    • 3 容器之分类与各种测试（一）：array
    • 4 容器之分类与各种测试（二）：vector
    • 5 容器之分类与各种测试（三）list, deque,stack, queue
    • 6 容器之分类与各种测试（四）：set和unordered_set等
    • 7 分配器之测试
    • 后记

本节主要介绍STL容器的使用方法
STL有很多容器，大概分类如下：

■ 标准STL序列容器
：vector、string、deque和list。
■ 标准STL关联容器
：set、multiset、map和multimap。
■ 非标准序列容器
slist和rope。slist是一个单向链表，rope本质上是一个“重型”string。
■ 非标准的关联容器
hash_set、hash_multiset、hash_map和hash_multimap。所有hash开头的，在c++11里面改名为unordered,比如unordered_set。

3 容器之分类与各种测试（一）：array

测试开50万大小的array，排序并且查找花费的时间。大概0.18秒。

const long ASIZE = 500000L;long get_a_target_long()
{
long target=0;cout << "target (0~" << RAND_MAX << "): ";cin >> target;return target;
}int compareLongs(const void* a, const void* b)
{return ( *(long*)a - *(long*)b );
}#include <array>
#include <iostream>
#include <ctime> 
#include <cstdlib> //qsort, bsearch, NULL
namespace jj01
{
void test_array()
{cout << "\ntest_array().......... \n";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;	// 得到array起始地址long target = get_a_target_long();timeStart = clock();::qsort(c.data(), ASIZE, sizeof(long), compareLongs); // 前面加双冒号：：表示全局函数
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;elsecout << "not found! " << endl;	
}
}

4 容器之分类与各种测试（二）：vector

测试vector：放入100万个元素到vector中，放入的时间大概是3秒。

vector当放入新元素的时候，如果空间不够，它会变成原来大小的两倍，即两倍增长。

#include <vector>
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()
#include <cstdio>  //snprintf()
#include <iostream>
#include <ctime> 
#include <algorithm> 	//sort()
namespace jj02
{
void test_vector(long& value)
{cout << "\ntest_vector().......... \n";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_allocabort();}}cout << "milli-seconds : " << (clock()-timeStart) << endl;	cout << "vector.max_size()= " << c.max_size() << endl;	//1073747823cout << "vector.size()= " << c.size() << endl;		// 真正元素的个数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;	//目前vector实际分配的空间有多大	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;elsecout << "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;elsecout << "not found! " << endl << endl;	}c.clear();test_moveable(vector<MyString>(),vector<MyStrNoMove>(), value);	
}	
}

5 容器之分类与各种测试（三）list, deque,stack, queue

使用容器list

list是双向链表，放入元素也是push_back

#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 << "\ntest_list().......... \n";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;    //357913941cout << "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;elsecout << "not found! " << endl;	timeStart = clock();		c.sort();						cout << "c.sort(), milli-seconds : " << (clock()-timeStart) << endl;		    	c.clear();test_moveable(list<MyString>(),list<MyStrNoMove>(), value);								
}	
}

使用容器forward_list

单向链表，它没有push_back,只有push_front函数

#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 << "\ntest_forward_list().......... \n";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;  //536870911cout << "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;elsecout << "not found! " << endl;	timeStart = clock();		c.sort();						cout << "c.sort(), milli-seconds : " << (clock()-timeStart) << endl;		c.clear();	 
}											 
}

使用容器slist

测试容器slist：slist也是单向链表

#include <ext\slist>	
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()
#include <cstdio>  //snprintf()
#include <iostream>
#include <ctime> 
namespace jj10
{
void test_slist(long& value)
{cout << "\ntest_slist().......... \n";__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;			
}															
}

使用容器deque

双端队列

deque底层是分段连续，但是对使用者来说是连续的。

#include <deque>
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()
#include <cstdio>  //snprintf()
#include <iostream>
#include <ctime> 
namespace jj05
{
void test_deque(long& value)
{cout << "\ntest_deque().......... \n";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;elsecout << "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);		 						
}															
}

使用容器stack

stack本身使用deque实现, stack是先进后出

#include <stack>
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()
#include <cstdio>  //snprintf()
#include <iostream>
#include <ctime> 
namespace jj17
{
void test_stack(long& value)
{cout << "\ntest_stack().......... \n";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> >'}															
}

使用容器queue

queue（队列）本身使用deque实现，queue先进先出

#include <queue>
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()
#include <cstdio>  //snprintf()
#include <iostream>
#include <ctime> 
namespace jj18
{
void test_queue(long& value)
{cout << "\ntest_queue().......... \n";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> >'	
}															
}

6 容器之分类与各种测试（四）：set和unordered_set等

使用容器multiset

Set和multiset会根据特定的排序准则，自动将元素排序。两者不同之处在于multiset允许元素重复而set不允许。

#include <set>
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()
#include <cstdio>  //snprintf()
#include <iostream>
#include <ctime> 
namespace jj06
{
void test_multiset(long& value)
{cout << "\ntest_multiset().......... \n";multiset<string> c;  	
char buf[10];		
clock_t timeStart = clock();								for(long i=0; i< value; ++i){try {snprintf(buf, 10, "%d", rand());c.insert(string(buf));     				}catch(exception& p) {cout << "i=" << i << " " << p.what() << endl;	abort();}}cout << "milli-seconds : " << (clock()-timeStart) << endl;	cout << "multiset.size()= " << c.size() << endl;	cout << "multiset.max_size()= " << c.max_size() << endl;	//214748364string target = get_a_target_string();	{timeStart = clock();
auto pItem = find(c.begin(), c.end(), target);	//比 c.find(...) 慢很多	cout << "std::find(), milli-seconds : " << (clock()-timeStart) << endl;		if (pItem != c.end())cout << "found, " << *pItem << endl;elsecout << "not found! " << endl;	}{timeStart = clock();		
auto pItem = c.find(target);		//比 std::find(...) 快很多							cout << "c.find(), milli-seconds : " << (clock()-timeStart) << endl;		 if (pItem != c.end())cout << "found, " << *pItem << endl;elsecout << "not found! " << endl;	}	c.clear();test_moveable(multiset<MyString>(),multiset<MyStrNoMove>(), value);	 						
}															 
}

使用容器multimap

Map和multimap将key/value pair当作元素进行管理。它们可根据key的排序准则自动为元素排序。Multimap允许重复元素，map不允许

#include <map>
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()
#include <cstdio>  //snprintf()
#include <iostream>
#include <ctime> 
namespace jj07
{
void test_multimap(long& value)
{cout << "\ntest_multimap().......... \n";multimap<long, string> c;  	
char buf[10];clock_t timeStart = clock();								for(long i=0; i< value; ++i){try {snprintf(buf, 10, "%d", rand());//multimap 不可使用 [] 做 insertion c.insert(pair<long,string>(i,buf));   						}catch(exception& p) {cout << "i=" << i << " " << p.what() << endl;	abort();}}cout << "milli-seconds : " << (clock()-timeStart) << endl;	cout << "multimap.size()= " << c.size() << endl;cout << "multimap.max_size()= " << c.max_size() << endl;	//178956970	long target = get_a_target_long();		timeStart = clock();		
auto pItem = c.find(target);								cout << "c.find(), milli-seconds : " << (clock()-timeStart) << endl;	 if (pItem != c.end())cout << "found, value=" << (*pItem).second << endl;elsecout << "not found! " << endl;	  c.clear();		  					
}															 
}

使用容器unordered_multiset

不是基于红黑树，而是基于hash table。允许重复的key存在

#include <unordered_set>
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()
#include <cstdio>  //snprintf()
#include <iostream>
#include <ctime> 
namespace jj08
{
void test_unordered_multiset(long& value)
{cout << "\ntest_unordered_multiset().......... \n";unordered_multiset<string> c;  	
char buf[10];clock_t timeStart = clock();								for(long i=0; i< value; ++i){try {snprintf(buf, 10, "%d", rand());c.insert(string(buf));   			  		}catch(exception& p) {cout << "i=" << i << " " << p.what() << endl;	abort();}}cout << "milli-seconds : " << (clock()-timeStart) << endl;		cout << "unordered_multiset.size()= " << c.size() << endl;cout << "unordered_multiset.max_size()= " << c.max_size() << endl;	//357913941cout << "unordered_multiset.bucket_count()= " << c.bucket_count() << endl;	// 桶的数量cout << "unordered_multiset.load_factor()= " << c.load_factor() << endl;	cout << "unordered_multiset.max_load_factor()= " << c.max_load_factor() << endl;	cout << "unordered_multiset.max_bucket_count()= " << c.max_bucket_count() << endl;				for (unsigned i=0; i< 20; ++i) {cout << "bucket #" << i << " has " << c.bucket_size(i) << " elements.\n";}					string target = get_a_target_string();	{timeStart = clock();
auto pItem = find(c.begin(), c.end(), target);	//比 c.find(...) 慢很多	cout << "std::find(), milli-seconds : " << (clock()-timeStart) << endl;	if (pItem != c.end())cout << "found, " << *pItem << endl;elsecout << "not found! " << endl;	}{timeStart = clock();		
auto pItem = c.find(target);		//比 std::find(...) 快很多							cout << "c.find(), milli-seconds : " << (clock()-timeStart) << endl;	 if (pItem != c.end())cout << "found, " << *pItem << endl;elsecout << "not found! " << endl;	}		c.clear();test_moveable(unordered_multiset<MyString>(),unordered_multiset<MyStrNoMove>(), value);		 	 							
}

使用容器unordered_multimap

允许重复的key存在

#include <unordered_map>
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()
#include <cstdio>  //snprintf()
#include <iostream>
#include <ctime> 
namespace jj09
{
void test_unordered_multimap(long& value)
{cout << "\ntest_unordered_multimap().......... \n";unordered_multimap<long, string> c;  	
char buf[10];clock_t timeStart = clock();								for(long i=0; i< value; ++i){try {snprintf(buf, 10, "%d", rand());//multimap 不可使用 [] 進行 insertion c.insert(pair<long,string>(i,buf));}catch(exception& p) {cout << "i=" << i << " " << p.what() << endl;	abort();}}cout << "milli-seconds : " << (clock()-timeStart) << endl;		cout << "unordered_multimap.size()= " << c.size() << endl;	cout << "unordered_multimap.max_size()= " << c.max_size() << endl;	//357913941	long target = get_a_target_long();		timeStart = clock();		
auto pItem = c.find(target);								cout << "c.find(), milli-seconds : " << (clock()-timeStart) << endl;		 if (pItem != c.end())cout << "found, value=" << (*pItem).second << endl;elsecout << "not found! " << endl;		
}															 
}

使用容器set

set中key不可重复

#include <set>
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()
#include <cstdio>  //snprintf()
#include <iostream>
#include <ctime> 
namespace jj13
{
void test_set(long& value)
{cout << "\ntest_set().......... \n";set<string> c;  	
char buf[10];clock_t timeStart = clock();								for(long i=0; i< value; ++i){try {snprintf(buf, 10, "%d", rand());c.insert(string(buf));     					}catch(exception& p) {cout << "i=" << i << " " << p.what() << endl;	abort();}}cout << "milli-seconds : " << (clock()-timeStart) << endl;		cout << "set.size()= " << c.size() << endl;cout << "set.max_size()= " << c.max_size() << endl;	   //214748364string target = get_a_target_string();	{timeStart = clock();
auto pItem = find(c.begin(), c.end(), target);	//比 c.find(...) 慢很多	cout << "std::find(), milli-seconds : " << (clock()-timeStart) << endl;		if (pItem != c.end())cout << "found, " << *pItem << endl;elsecout << "not found! " << endl;	}{timeStart = clock();		
auto pItem = c.find(target);		//比 std::find(...) 快很多							cout << "c.find(), milli-seconds : " << (clock()-timeStart) << endl;		 if (pItem != c.end())cout << "found, " << *pItem << endl;elsecout << "not found! " << endl;	}							
}															 
}

使用容器map

底部是红黑树，存的元素是不能重复的

#include <map>
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()
#include <cstdio>  //snprintf()
#include <iostream>
#include <ctime> 
namespace jj14
{
void test_map(long& value)
{cout << "\ntest_map().......... \n";map<long, string> c;  	
char buf[10];clock_t timeStart = clock();								for(long i=0; i< value; ++i){try {snprintf(buf, 10, "%d", rand());c[i] = string(buf);  					}catch(exception& p) {cout << "i=" << i << " " << p.what() << endl;	abort();}}cout << "milli-seconds : " << (clock()-timeStart) << endl;	cout << "map.size()= " << c.size() << endl;	cout << "map.max_size()= " << c.max_size() << endl;		//178956970long target = get_a_target_long();		timeStart = clock();		
auto pItem = c.find(target);								cout << "c.find(), milli-seconds : " << (clock()-timeStart) << endl;		 if (pItem != c.end())cout << "found, value=" << (*pItem).second << endl;elsecout << "not found! " << endl;			c.clear();					
}															 
}

使用容器 unordered_set

底层实现是hash table.

#include <unordered_set>
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()
#include <cstdio>  //snprintf()
#include <iostream>
#include <ctime> 
namespace jj15
{
void test_unordered_set(long& value)
{cout << "\ntest_unordered_set().......... \n";unordered_set<string> c;  	
char buf[10];clock_t timeStart = clock();								for(long i=0; i< value; ++i){try {snprintf(buf, 10, "%d", rand());c.insert(string(buf));    			 		}catch(exception& p) {cout << "i=" << i << " " << p.what() << endl;	abort();}}cout << "milli-seconds : " << (clock()-timeStart) << endl;		cout << "unordered_set.size()= " << c.size() << endl;	cout << "unordered_set.max_size()= " << c.max_size() << endl;  //357913941cout << "unordered_set.bucket_count()= " << c.bucket_count() << endl;	cout << "unordered_set.load_factor()= " << c.load_factor() << endl;	cout << "unordered_set.max_load_factor()= " << c.max_load_factor() << endl;	cout << "unordered_set.max_bucket_count()= " << c.max_bucket_count() << endl;			for (unsigned i=0; i< 20; ++i) {cout << "bucket #" << i << " has " << c.bucket_size(i) << " elements.\n";}			string target = get_a_target_string();	{timeStart = clock();
auto pItem = find(c.begin(), c.end(), target);	//比 c.find(...) 慢很多	cout << "std::find(), milli-seconds : " << (clock()-timeStart) << endl;		if (pItem != c.end())cout << "found, " << *pItem << endl;elsecout << "not found! " << endl;	}{timeStart = clock();		
auto pItem = c.find(target);		//比 std::find(...) 快很多							cout << "c.find(), milli-seconds : " << (clock()-timeStart) << endl;		 if (pItem != c.end())cout << "found, " << *pItem << endl;elsecout << "not found! " << endl;	}	
}															 
}

使用容器unordered_map

底层实现是hash table。

#include <unordered_map>
#include <stdexcept>
#include <string>
#include <cstdlib> //abort()
#include <cstdio>  //snprintf()
#include <iostream>
#include <ctime> 
namespace jj16
{
void test_unordered_map(long& value)
{cout << "\ntest_unordered_map().......... \n";unordered_map<long, string> c;  	
char buf[10];clock_t timeStart = clock();								for(long i=0; i< value; ++i){try {snprintf(buf, 10, "%d", rand());c[i] = string(buf);  		}catch(exception& p) {cout << "i=" << i << " " << p.what() << endl;	abort();}}cout << "milli-seconds : " << (clock()-timeStart) << endl;		cout << "unordered_map.size()= " << c.size() << endl;	//357913941cout << "unordered_map.max_size()= " << c.max_size() << endl;	long target = get_a_target_long();		timeStart = clock();	
//! auto pItem = find(c.begin(), c.end(), target);	//map 不適用 std::find() 			
auto pItem = c.find(target);cout << "c.find(), milli-seconds : " << (clock()-timeStart) << endl;		 if (pItem != c.end())cout << "found, value=" << (*pItem).second << endl;elsecout << "not found! " << endl;		
}															 
}

7 分配器之测试

使用容器的时候，如果没有显式指定分配器，会使用默认的分配器。

在这里插入图片描述

#include <list>
#include <stdexcept>
#include <string>
#include <cstdlib> 		//abort()
#include <cstdio>  		//snprintf()
#include <algorithm> 	//find()
#include <iostream>
#include <ctime> #include <cstddef>
#include <memory>	//內含 std::allocator  //欲使用 std::allocator 以外的 allocator, 得自行 #include <ext\...> 
#ifdef __GNUC__		
#include <ext\array_allocator.h>
#include <ext\mt_allocator.h>
#include <ext\debug_allocator.h>
#include <ext\pool_allocator.h>
#include <ext\bitmap_allocator.h>
#include <ext\malloc_allocator.h>
#include <ext\new_allocator.h>  
#endifnamespace jj20
{
//pass A object to function template impl()，
//而 A 本身是個 class template, 帶有 type parameter T,  
//那麼有無可能在 impl() 中抓出 T, 創建一個 list<T, A<T>> object? 
//以下先暫時迴避上述疑問.void test_list_with_special_allocator()
{
#ifdef __GNUC__	cout << "\ntest_list_with_special_allocator().......... \n";//不能在 switch case 中宣告，只好下面這樣. 				//1000000次 list<string, allocator<string>> c1;						//3140list<string, __gnu_cxx::malloc_allocator<string>> c2;  	//3110list<string, __gnu_cxx::new_allocator<string>> c3; 		//3156list<string, __gnu_cxx::__pool_alloc<string>> c4;  		//4922list<string, __gnu_cxx::__mt_alloc<string>> c5; 		//3297list<string, __gnu_cxx::bitmap_allocator<string>> c6;  	//4781 														int choice;
long value;     cout << "select: "<< " (1) std::allocator "<< " (2) malloc_allocator "<< " (3) new_allocator "<< " (4) __pool_alloc "<< " (5) __mt_alloc "<< " (6) bitmap_allocator ";cin >> choice;if ( choice != 0 ) {cout << "how many elements: ";cin >> value; 		}char buf[10];			
clock_t timeStart = clock();								for(long i=0; i< value; ++i){try {snprintf(buf, 10, "%d", i);switch (choice) {case 1 : 	c1.push_back(string(buf)); 	break;case 2 : 	c2.push_back(string(buf)); 	break;		case 3 : 	c3.push_back(string(buf)); break;		case 4 : 	c4.push_back(string(buf)); 	break;		case 5 : 	c5.push_back(string(buf)); 		break;		case 6 : 	c6.push_back(string(buf)); 	break;				default: break;		}    		   		}catch(exception& p) {cout << "i=" << i << " " << p.what() << endl;	abort();}}cout << "a lot of push_back(), milli-seconds : " << (clock()-timeStart) << endl;	//test all allocators' allocate() & deallocate();int* p; 	allocator<int> alloc1;	p = alloc1.allocate(1);  alloc1.deallocate(p,1); 	__gnu_cxx::malloc_allocator<int> alloc2;  p = alloc2.allocate(1);  alloc2.deallocate(p,1);  	__gnu_cxx::new_allocator<int> alloc3; 	p = alloc3.allocate(1);  alloc3.deallocate(p,1); 	__gnu_cxx::__pool_alloc<int> alloc4;  	p = alloc4.allocate(2);  alloc4.deallocate(p,2); 	//我刻意令參數為 2, 但這有何意義!! 一次要 2 個 ints? __gnu_cxx::__mt_alloc<int> alloc5; 	p = alloc5.allocate(1);  alloc5.deallocate(p,1);  	__gnu_cxx::bitmap_allocator<int> alloc6;  	p = alloc6.allocate(3);  alloc6.deallocate(p,3);  	//我刻意令參數為 3, 但這有何意義!! 一次要 3 個 ints? 
#endif 			
}															
}

后记

这是STL标准库与泛型编程（侯捷）的第一份笔记，后续笔记会陆续更新。

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