c++標準庫體系結構與內核分析
第一講：示范運用STL各大部件 (components)，并初步認識其體系結構
1.認識headers、版本、重要資源
所謂generic programing，GP泛型編程，就是使用template模板為主要工具來編寫程序
根據源代碼分析c++STL之體系結構
應具備的基礎：c++基本語法，包括如何正確使用模板templates
-level0：使用c++標準庫
-level1：深入認識c++標準庫，清楚其在內存中的結構等
-level2：良好使用c++標準庫
-level3：擴充c++標準庫
c++標準庫與STL
-c++ standard library：目前c++中已給的頭文件
-standard template library：標準模板庫，分為六大部件，標準庫中大量存在STL
-標準庫以Header files形式呈現，所以源代碼可見
-headers中的組件封裝于namespace std
using namespace std;
using std::cout;
#include <string>
#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>
using namespace std;
不同版本標準庫的用法基本相同
推薦網站：
-www.cplusplus.com
-en.cppreference.com
-gcc.gnu.org
2.STL體系結構基礎介紹
STL六大部件：
-容器containers
-分配器allocators
-算法algorithms
-迭代器iterators
-適配器adapters
-仿函式functors
分配器用來支持容器存放
部分操作在容器本身操作另外部分放在算法操作
面向對象編程中鼓勵將數據及函數放在類中，與STL不同
容器用來存放要處理的數據，算法對容器中的數據進行處理
迭代器是數據與操作的橋梁，是一種泛化的指針
仿函數作用像函數一樣
適配器用來幫助轉換，迭代器適配、仿函數適配、容器適配
#include <vector> //需要使用容器要引入對應的頭文件
#include <algorithm>
#include <functional>
#include <iostream>
using namespace std;
int main()
{
int ia[6]={27,210,12,47,109,83};
vector<int,allocator<int>> vi(ia,ia+6);
//容器↑ 分配器↑
//模板：尖括號中第一個參數為類型，第二個參數允許放一個分配器幫助分配內存，不寫的話使用默認
cout<<count_if(vi.begin(),vi.end,not1(bind2nd(less<int>(),40)));
// 算法↑ 迭代器↑ 適配器↑
//對數據的操作：需要用適配器來做容器和算法的接口
//predicate
return 0;
}
復雜度complexity
-O（1）、O（c）：常數時間 constant time
-O（n）：線性時間 linear time
-O（log2n）：次線性實踐 sub-linear time
-O（n^2）：平方時間 quadratic time
-O（n^3）：立方時間 cubic time
-O（2^n）：指數時間 exponential time
-O（nlog2n）：介于線性及二次方成長的中間
“前閉后開”區間
標準庫規定，容器中頭指針指向第一個元素，尾指針所指為容器最后元素的下一個位置
容器中的空間并不一定連續，也可能是鏈表或者哈希表
Container<T> c;
...
Container<T>::iterator ite = c.begin();
//容器都有其專屬的一個iterator，用其類型聲明頭指針
for(;ite!=c.end();ite++)
...
//對容器進行遍歷
c++11新功能：
-對容器進行遍歷
range-based "for" statement (since C++11)
for(decl:coll){statement}
for(int i : {2,3,5,7,9,13,17,19})
{
std::cout<<i<<std::endl;
}
std::vector<double> vec;
for(auto elem : vec)
{
std::cout<<elem<<std::endl;
}
for(auto& elem : vec)
{
elem *= 3;
}
-auto keyword
list<string> c;
...
list<string>::iterator ite;
ite=::find(c.begin(),c.end(),/*target*/);
↓
list<string> c;
...
auto ite = ::find(c.begin(),c.end(),/*target*/);
3.容器之分類與各種測試
容器-結構
-順序表
-鏈表
-樹
-堆
-哈希表
容器-分類
sequence containers
associative containers
unordered containers
hash table separate chaining
-array，固定大小，不可擴充
-vector，開頭固定，尾可擴充
-list，雙鏈表，雙向都有指針
-forward_list，單鏈表，指針為單向
-slist
-deque，頭尾可擴充
-stack
-multiset，集合中元素可重復
-multimap
-unordered_multiset，分散無序存放，
-unordered_multimap
-set，集合，一種平衡二叉樹，每個元素中key和value為同一個，集合中元素不可重復
-map，圖，通常用紅黑樹，每個元素中key和value為不同變量
-unordered_set
-unordered_map
-hash_set，哈希結構，目前最優
-hash_multiset
-hash_multimap
四個函數
-輸入一個target
-輸入一個字符串target
-比較兩個long型大小
-比較兩個字符串大小
使用容器array
#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;
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;
}
}
array
-尖括號中第一個參數為類型，第二個參數為容器大小
使用容器vector
#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_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);
}
}
-tips：測試程序的每一段歸在一個namespace中
vector
-尖括號中的參數為類型
使用容器list
#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; //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);
}
}
list
-尖括號參數為類型
循環存入數據
4.分配器之測試
使用分配器allocator
不同容器在聲明時候的分配方式
-尖括號第二位置的參數即是所選用的分配器
#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>
#endif
namespace 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; //3140
list<string, __gnu_cxx::malloc_allocator<string>> c2; //3110
list<string, __gnu_cxx::new_allocator<string>> c3; //3156
list<string, __gnu_cxx::__pool_alloc<string>> c4; //4922
list<string, __gnu_cxx::__mt_alloc<string>> c5; //3297
list<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
}
}
