本文主要是介绍STL标准库与泛型编程（侯捷）笔记1，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
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。
#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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