侯捷C++STL源码分析

目录

• STL六大部件
• 复杂度 Complexity，Big-oh
• 前闭后开区间
• range-based for statement (since C++11)
• auto key
• 容器——结构及分类
  • Sequence Contaioners(序列式容器)
  • Associative Containers(关联式容器)适合快速查找
• Unordered Containers（HashTable）
• 一次测试程序之辅助函数
  • 使用容器array
• 使用容器Vector
• 使用容器list

 

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STL六大部件

• 容器(Containers)：放东西，需要占用内存。

• 分配器(Allocators)：支持容器。

• 算法(Algorithms):操作容器里面的数据。

• 迭代器(Iterators):容器和算法之间的桥梁，泛化的指针。

• 适配器(A dapters)

• 仿函数(Functors)

#include<vector>
#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)//vector<类型,分配器(/*一般不会写*/)>
 cout<<cout_if(vi.begin(),vi.end(),not1(bind2nd(less<int>(),40)));//其中cout_if为algorithm,not1为functionadapter(negator) bind2nd为functionadapter(binder) less<int>为functionobject
 return 0;
}

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复杂度 Complexity，Big-oh

O(1)或O(c)常数时间(constant time)

O(n):称为线性时间(linear time)

O(log2 n)称为二次线性时间（sub—linlear time）

O(n*n)称为平方时间（quadratic time）

O(nnn)称为立方时间(cubic time)

O(2的n次方)称为指数时间

O(nlog2 n)：

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前闭后开区间

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range-based for statement (since C++11)

for(decl:coll){
  statement  
}

for(int i :{2,3,57,9,13,17,19}){
    std::cout<<i<<std::endl;
}

std::vector<double> vec;
...
for(auto elem:vec){
   std::cout<<elem<<std::endl;
}
for(auto& elem:vec){
  elem *= 3;
}

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auto key

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);

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容器——结构及分类

Sequence Contaioners(序列式容器)

Array：数组(c++11增加的，连续空间)

Vector:动态数组(分配器去处理)

Deque:双向队列(先进先出)

List：双向链表

Forward-List:单向链表

Associative Containers(关联式容器)适合快速查找

Set/Multiset(红黑树是高度平衡二叉树，Set放的元素不能重复,Multiset放的元素可以重复)

Map/Multimap（key:value）

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Unordered Containers（HashTable）

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一次测试程序之辅助函数

using std::cin;
using std::cout;
using std::string;
long get_a_target_long()
{
  long target = 0 ;
  cout<<"target 0~"<<RAND_MAX<<"):";
  cin>>target;
  return target;
}

string get_a_target_string()
{
  long target =  0 ; 
  char buf[10];
  cout <<"target (0~"<<RAND_MAX<<"):"
  cin>> target;
  snprintf(buf,10,"%d",target);//把后面的字符串赋值给buf，长度为min(10,后面那个字符串长度)-1
  return string(buf);
}

int compareLongs(const void* a,const void* b)
{
return (*(long*)a - *(long*)b);
}

使用容器array

#include<array>
#include<iostream>
#include<ctime>
#include<cstdlib>//qsort bsearch NULL
namespace jj01
{
void test_arry()
{
  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,siezeof(long), compareLongs);
cout<<"qsort()+bsearch(),milli-seconds:"<<(clock()-timeStart)<<endl;//要使用二分查找之前，数据一定要排序
if(pItem != NULL)
  cout<<"found,"<<*pItem<<endl;
else
  cout<<"not found"<<endl;
}
}

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使用容器Vector

#include<vector>
#include<stdexcept>
#include<string>
#include<cstdlib>
#include<cstdio>
#include<iostream>
#include<ctime>
#include<algorithm>
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;
  //曾经最高i=58389486 then std::dac_alloc  
   abort();
}
}
cout <<"milli-seconds:"<<(clock()-timeStart)<<endl;
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;
  string target = get_a_target_string();
  {
  timeStart = clock();
  auto pItem=::find(c.begin,c.end(),target);
//find模板函数跟普通函数是一样的。其中双冒号是一个全局的东西
if(pItem != c.end())
  cout<<"found,"<<*pItem<<endl;
else
  cout<<"not found!" <<endl;
  }
{
timeStart = clock();
sort(c.begin,c,end())
string* pItem = (string*) bsearch(&target,(c.data()),c.size(),sizeof(string)),compareLongs);
cout<<"sort()+bsearch(),milli-seconds:"<<(clock-timeStart);
  if(pItem != NULL)
  cout<<"found,"<<*pItem<<endl;
  else 
  cout<<"not found" <<endl;
}
}
}
//总结:不一定排序+二分查找 查找速度就快。

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使用容器list

#include<vector>
#include<stdexcept>
#include<string>
#include<cstdlib>
#include<cstdio>
#include<iostream>
#include<ctime>
#include<algorithm>
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;
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<<"::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;
}
}