STL源码剖析-map

1.容器rb_tree

Red-Black tree（红黑树）是平衡二元搜寻树（balanced binary search tree）中常被使用的一种平衡二元搜寻树的特点：排列规则有利于search和insert，并保持适度平衡-无任何节点过深

rb_tree提供遍历操作以及iterators

按正常规则（++ite）遍历，便能获得排序状态（sorted）

我们不应该使用rb_tree的iterators改变元素值（因为元素有其严谨排列规则）。编程里面（programming leve）并未阻绝此事。如此设计是正确的，因为rb_tree即将为set和map服务（做为其底部支持），而map允许元素的data被改变，只有元素的key才是不可被改变的

rb_tree提供两种insertion操作:insert_unique()和insert_equal()。前者表示节点的key一定在整个tree中独一无二，否则安插失败。后者表示节点的key可重复

#include <set>
#include <iostream>
using namespace std;
//容器rb_tree
// key和data合成value(key|value)
//template<class Key, class Value, class KeyOfValue, class Compare, class Alloc = alloc>
//class rb_tree {
//protected:
// typedef __rb_tree_node<Value> rb_tree_node;
// ...
//public:
// typedef rb_tree_node* link_type;
//protected:
// //RB-tree只以三笔表现他自己
// size_type node_count; // rb_tree的大小(节点)
// link_type header;
// Compare key_compare; //key的大小比较规则,应会是个function object
//};
namespace jj31
{
void test_Rb_tree()
{
//G2.9 vs. G4.9 :
//rb_tree => _Rb_tree,
//identity<> => _Identity<>
//insert_unique() => _M_insert_unique()
//insert_equal() => _M_insert_equal()
cout << "\ntest_Rb_tree().......... \n";
_Rb_tree<int, int, _Identity<int>, less<int> > itree;
cout << itree.empty() << endl; //1
cout << itree.size() << endl; //0
itree._M_insert_unique(3);
itree._M_insert_unique(8);
itree._M_insert_unique(5);
itree._M_insert_unique(9);
itree._M_insert_unique(13);
itree._M_insert_unique(5); //no effect, since using insert_unique().
cout << itree.empty() << endl; //0
cout << itree.size() << endl; //5
cout << itree.count(5) << endl; //1
itree._M_insert_equal(5);
itree._M_insert_equal(5);
cout << itree.size() << endl; //7, since using insert_equal().
cout << itree.count(5) << endl; //3
}
}
int main() {
jj31::test_Rb_tree();
return 0;
}

2.容器map，multimap

（1）map/multimap以rb_tree为底层结构,因此有元素自动排序特性,排序的依据是key.
（2）map/multimap提供"遍历"操作及iterators,按正常规则(++ite)遍历,便能获得排序状态(sorted)
（3）我们无法使用map/multimap的iterators改变元素的key(因为key有其严谨的排列规则),但可以用它改变元素的data,
因此,map/multimap内部自动将user指定的key type设为const,如此禁止user对元素的key赋值，map不允许迭代器来改key

（4）map元素的key必须独一无二,因此其insert()用的是rb_tree的insert_unique
multimap元素的key可以重复,因此其insert()用的是rb_tree的insert_equal

template <class _Key, class _Tp, class _Compare, class _Alloc>
class map {
public:
// typedefs:
typedef _Key key_type;
typedef _Tp data_type;
typedef _Tp mapped_type;
typedef pair<const _Key, _Tp> value_type;
// key|data,key和data合成value
// map/multimap内部自动将user指定的key type设为const,如此禁止user对元素的key赋值
typedef _Compare key_compare;
private:
typedef _Rb_tree<key_type, value_type,
_Select1st<value_type>, key_compare, _Alloc> _Rep_type;
_Rep_type _M_t; // red-black tree representing map
public:
typedef typename _Rep_type::iterator iterator;
};
map<int, string> imap -> map<int, string, less<int>, alloc> imap ->
template<int, pair<const int, string>, select1st<pair<const int, string>>, less<int>, alloc> class rb_tree;

3.容器map，独特的operator[]

返回与下标中指定的键关联的数据
如果key不存在，则使用默认值创建具有key的对，然后返回该值

_Tp& operator[](const key_type& __k) {
iterator __i = lower_bound(__k);
// __i->first is greater than or equivalent to __k.
if (__i == end() || key_comp()(__k, (*__i).first))
__i = insert(__i, value_type(__k, _Tp()));
return (*__i).second;
}

lower_bound是二分搜寻的一种版本,试图在sorted[first, last)中寻找元素value
若[first, last)拥有value相等的元素(s),便返回一个iterator指向其中第一个元素
如果没有这样的元素存在,便返回假设该元素存在时应该出现的位置
lower_bound返回的是不破坏排序得以安插value的第一个适当位置

#include <map>
#include <stdexcept>
#include <string>
#include <cstdlib> //abort() and rand() and RAND_MAX
#include <cstdio> //snprintf()
#include <iostream>
#include <ctime>
using namespace std;
namespace jj14
{
long get_a_target_long()
{
long target=0;
cout << "target (0~" << RAND_MAX << "): ";
cin >> target;
return target;
}
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; //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;
else
cout << "not found! " << endl;
c.clear();
}
}
int main() {
long value;
cout << "how many elements: ";
cin >> value;
jj14::test_map(value);
}

4.map容器迭代器失效问题

迭代器失效_INGNIGHT的博客-CSDN博客

#include <iostream>
#include <map>
using namespace std;
class Key {
public:
explicit Key(int num):_num(num) {
}
int get_num() const {
return _num;
}
bool operator < (const Key& k) const {
return get_num() < k.get_num() ? true : false;
}
public:
int _num;
};
class CompareKey : public binary_function<Key, Key, bool> {
public:
bool operator()(const Key& k1, const Key& k2) {
return k1.get_num() < k2.get_num() ? true : false;
}
};
int main() {
//std::map<Key, int, CompareKey> table;
std::map<Key, int> table;
table.insert(std::pair<Key, int>(Key(0), 1));
table.insert(std::pair<Key, int>(Key(1), 1));
table.insert(std::pair<Key, int>(Key(3), 1));
table.insert(std::pair<Key, int>(Key(4), 1));
table.insert(std::pair<Key, int>(Key(5), 1));
cout << table.begin()->first.get_num() << std::endl;
cout << table.rbegin()->first.get_num() << std::endl;
auto ite = table.lower_bound(Key(1));
cout << ite->first.get_num() << std::endl;;
ite = table.lower_bound(Key(2));
cout << ite->first.get_num() << std::endl;;
ite = table.upper_bound(Key(2));
cout << ite->first.get_num() << std::endl;;
ite = table.upper_bound(Key(1));
cout << ite->first.get_num() << std::endl;;
}

STL源码剖析-map_stl map源码、-CSDN博客