C++STL之map学习

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map<Key, Data, Compare, Alloc>

 

map是一种关联容器，存储相结合形成的一个关键值和映射值的元素。Map 是一种Pair Associative Container，意味着它的值类型为 pair<const Key, Data>. 而且也是 Unique Associative Container, 也就是任何两个元素没有相同的key值。

map具有重要的属性，就是在map对象中插入一个新元素不指向现有元素的迭代器失效。从map上删除一个元素，也没有任何迭代器失效，除非，当然，实际上指向正在被删除的元素的迭代器。

 

1、例子

struct ltstr
{
  bool operator()(const char* s1, const char* s2) const
  {
    return strcmp(s1, s2) < 0;
  }
};

int main()
{
  map<const char*, int, ltstr> months;
  
  months["january"] = 31;
  months["february"] = 28;
  months["march"] = 31;
  months["april"] = 30;
  months["may"] = 31;
  months["june"] = 30;
  months["july"] = 31;
  months["august"] = 31;
  months["september"] = 30;
  months["october"] = 31;
  months["november"] = 30;
  months["december"] = 31;
  
  cout << "june -> " << months["june"] << endl;
  map<const char*, int, ltstr>::iterator cur  = months.find("june");
  map<const char*, int, ltstr>::iterator prev = cur;
  map<const char*, int, ltstr>::iterator next = cur;    
  ++next;
  --prev;
  cout << "Previous (in alphabetical order) is " << (*prev).first << endl;
  cout << "Next (in alphabetical order) is " << (*next).first << endl;
}

 

2、定义形式

template < class Key, class T, class Compare = less<Key>,
           class Allocator = allocator<pair<const Key,T> > > class map;

 

3、模板参数具有以下涵义：

key：关键值的类型。在map对象中的每个元素是通过该关键值唯一确定元素的。
T：映射值的类型。在map中的每个元素是用来储存一些数据作为其映射值。
compare：Comparison类：A类键的类型，它有两个参数，并返回一个bool。表达comp（A，B），comp是这比较类A和B是关键值的对象，应返回true，如果是在早先的立场比B放置在一个严格弱排序操作。这可以是一个类实现一个函数调用运算符或一个函数的指针（见一个例子构造）。默认的对于<KEY>，返回申请小于操作符相同的默认值（A <B）。
Map对象使用这个表达式来确定在容器中元素的位置。以下这个规则在任何时候都排列在map容器中的所有元素。
Allocator：用于定义存储分配模型分配器对象的类型。默认情况下，分配器类模板，它定义了最简单的内存分配模式，是值独立的

 

map<Key,T>::iterator it;
(*it).first;             // 指向key值(of type Key)
(*it).second;            // 映射的值(of type T)
(*it);                   // the "element value" (of type pair<const Key,T>) 

也可以如下表达：

it->first;               // same as (*it).first   (the key value)
it->second;              // same as (*it).second  (the mapped value)

 

 

4、成员变量和成员函数

Member	Where defined	Description
key_type	Associative Container	map中的key类型
data_type	Pair Associative Container	key关联的值类型
value_type	Pair Associative Container	对象类型, pair<const key_type, data_type>,存储在map中
key_compare	Sorted Associative Container	Function object 通过顺序比较
value_compare	Sorted Associative Container	Function object that compares two values for ordering.
pointer	Container	Pointer to T.
reference	Container	Reference to T
const_reference	Container	Const reference to T
size_type	Container	An unsigned integral type.
difference_type	Container	A signed integral type.
iterator	Container	Iterator used to iterate through a map. [1]
const_iterator	Container	Const iterator used to iterate through a map.
reverse_iterator	Reversible Container	Iterator used to iterate backwards through a map. [1]
const_reverse_iterator	Reversible Container	Const iterator used to iterate backwards through a map.
iterator begin()	Container	Returns an iterator pointing to the beginning of the map.
iterator end()	Container	Returns an iterator pointing to the end of the map.
const_iterator begin() const	Container	Returns a const_iterator pointing to the beginning of themap.
const_iterator end() const	Container	Returns a const_iterator pointing to the end of the map.
reverse_iterator rbegin()	Reversible Container	Returns a reverse_iterator pointing to the beginning of the reversed map.
reverse_iterator rend()	Reversible Container	Returns a reverse_iterator pointing to the end of the reversed map.
const_reverse_iterator rbegin() const	Reversible Container	Returns a const_reverse_iterator pointing to the beginning of the reversed map.
const_reverse_iterator rend() const	Reversible Container	Returns a const_reverse_iterator pointing to the end of the reversed map.
size_type size() const	Container	Returns the size of the map.
size_type max_size() const	Container	Returns the largest possible size of the map.
bool empty() const	Container	true if the map's size is 0.
key_compare key_comp() const	Sorted Associative Container	Returns the key_compare object used by the map.
value_compare value_comp() const	Sorted Associative Container	Returns the value_compare object used by the map.
map()	Container	Creates an empty map.
map(const key_compare& comp)	Sorted Associative Container	Creates an empty map, using comp as the key_compare object.
template <class InputIterator> map(InputIterator f, InputIterator l)	Unique Sorted Associative Container	Creates a map with a copy of a range.
template <class InputIterator> map(InputIterator f, InputIterator l, const key_compare& comp)	Unique Sorted Associative Container	Creates a map with a copy of a range, using comp as thekey_compare object.
map(const map&)	Container	The copy constructor.
map& operator=(const map&)	Container	The assignment operator
void swap(map&)	Container	Swaps the contents of two maps.
pair<iterator, bool> insert(const value_type& x)	Unique Associative Container	Inserts x into the map.
iterator insert(iterator pos, const value_type& x)	Unique Sorted Associative Container	Inserts x into the map, using pos as a hint to where it will be inserted.
template <class InputIterator> void insert(InputIterator, InputIterator) [2]	Unique Sorted Associative Container	Inserts a range into the map.
void erase(iterator pos)	Associative Container	Erases the element pointed to by pos.
size_type erase(const key_type& k)	Associative Container	Erases the element whose key is k.
void erase(iterator first, iterator last)	Associative Container	Erases all elements in a range.
void clear()	Associative Container	Erases all of the elements.
iterator find(const key_type& k)	Associative Container	Finds an element whose key is k.
const_iterator find(const key_type& k) const	Associative Container	Finds an element whose key is k.
size_type count(const key_type& k)	Unique Associative Container	Counts the number of elements whose key is k.
iterator lower_bound(const key_type& k)	Sorted Associative Container	Finds the first element whose key is not less than k.
const_iterator lower_bound(const key_type& k) const	Sorted Associative Container	Finds the first element whose key is not less than k.
iterator upper_bound(const key_type& k)	Sorted Associative Container	Finds the first element whose key greater than k.
const_iterator upper_bound(const key_type& k) const	Sorted Associative Container	Finds the first element whose key greater than k.
pair<iterator, iterator> equal_range(const key_type& k)	Sorted Associative Container	Finds a range containing all elements whose key is k.
pair<const_iterator, const_iterator> equal_range(const key_type& k) const	Sorted Associative Container	Finds a range containing all elements whose key is k.
data_type& operator[](const key_type& k) [3]	map	See below.
bool operator==(const map&, const map&)	Forward Container	Tests two maps for equality. This is a global function, not a member function.
bool operator<(const map&, const map&)	Forward Container	Lexicographical comparison. This is a global function, not a member function.

下面展示了常用的一些方法。

// stu_map.cpp : 定义控制台应用程序的入口点。 // #include "stdafx.h" #include <iostream> #include <map> using namespace std; bool fncomp(char lhs,char rhs) { return lhs<rhs; } struct classcomp { bool operator()(const char& lhs,const char& rhs) { return lhs<rhs; } }; int _tmain(int argc, _TCHAR* argv[]) { map<char,int> mymap; mymap['a']=10; mymap['b']=60; mymap['c']=30; mymap['d']=90; mymap['e']=50; map<char,int> second(mymap); map<char,int> third(mymap.begin(),mymap.end()); map<char,int,classcomp> fourth; bool(*fn_pt)(char,char)=fncomp; map<char,int,bool(*)(char,char)> fifth(fn_pt); map<char,int>::key_compare key_comp; map<char,int>::iterator it; it=mymap.begin(); for (it;it!=mymap.end();it++) { cout<<it->first<<":"<<it->second<<endl; } cout<<"================================="<<endl; second.clear(); second['a']=1002; second['b']=10023; while (!second.empty()) { cout << second.begin()->first << " => "; cout << second.begin()->second << endl; second.erase(second.begin()); } cout<<"================================="<<endl; mymap.insert(pair<char,int>('f',100) ); mymap.insert(pair<char,int>('g',200) ); cout<<"f => " <<mymap.find('f')->second<<endl; cout<<"g => " <<mymap.find('g')->second<<endl; cout<<"================================="<<endl; key_comp=mymap.key_comp(); cout << "mymap contains:\n"; char highest=mymap.rbegin()->first; // key value of last element it=mymap.begin(); do { cout << (*it).first << " => " << (*it).second << endl; } while ( key_comp((*it++).first, highest) ); cout << endl; return 0; }

运行结果：