C++stl map学习

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

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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

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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



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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：

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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 amap.
iterator begin()	Container	Returns an iterator pointing to the beginning of the map.
iterator end()	Container	Returns an iterator pointing to the end of themap.
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 themap.
map()	Container	Creates an empty map.
map(const key_compare& comp)	Sorted Associative Container	Creates an empty map, using comp as thekey_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 compas 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 thank.
const_iterator lower_bound(const key_type& k) const	Sorted Associative Container	Finds the first element whose key is not less thank.
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.

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下面展示了常用的一些方法。<p>// 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;

}



</p>

运行结果：


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