C++ map容器详解与应用示例-优快云博客

本文链接：https://blog.youkuaiyun.com/wunghao8/article/details/40893139

本文介绍了C++中的map容器，它是一个键值对容器，用于存储Key-Value对。文章详细讲解了map的定义、常用函数，并通过示例展示了如何插入数据、查询和修改数据。通过一个实例，解释了如何利用map统计用户输入一行文字中每个单词出现的次数。

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在C++中map容器是一个键值对容器，也就是一个Key对应一个Value，例如：(1,"hello)，或者也可以是这样：("hello2",2)，其中一个值为Key,第二个值为Value,在上面的例子中1和“hello2"是Key,当然它们对应的”hello"和2就是Value。

1、map定义在头文件<map>中，使用时要#include <map>;

2、声明时要使用类似这样的形式：map<int,string> testmap;或者map<stirng,string> testmap;等等。

3、map中支持的函数有：

Iterators:

begin

Return iterator to beginning (public member function )

end

Return iterator to end (public member function )

rbegin

Return reverse iterator to reverse beginning (public member function )

rend

Return reverse iterator to reverse end (public member function )

cbegin

Return const_iterator to beginning (public member function )

cend

Return const_iterator to end (public member function )

crbegin

Return const_reverse_iterator to reverse beginning (public member function )

crend

Return const_reverse_iterator to reverse end (public member function )

Capacity:

empty

Test whether container is empty (public member function )

size

Return container size (public member function )

max_size

Return maximum size (public member function )

Element access:

operator[]

Access element (public member function )

Modifiers:

insert

Insert elements (public member function )

erase

Erase elements (public member function )

swap

Swap content (public member function )

clear

Clear content (public member function )

emplace

Construct and insert element (public member function )

emplace_hint

Construct and insert element with hint (public member function )

Observers:

key_comp

Return key comparison object (public member function )

value_comp

Return value comparison object (public member function )

Operations:

find

Get iterator to element (public member function )

count

Count elements with a specific key (public member function )

lower_bound

Return iterator to lower bound (public member function )

upper_bound

Return iterator to upper bound (public member function )

equal_range

Get range of equal elements (public member function )

Allocator:

get_allocator

Get allocator (public member function )

4、插入数据时一般使用下面几种方法：

map<int,string> testmap1;

map<string,int> testmap2;

(1)   testmap2["a"] = 1; //当然你得保证有“a”这个Key!
(2)   testmap2.insert(map<string,int>::value_type("b",2)); 
(3)   testmap2.insert(pair<string,int>("c",3)); 
(4)   testmap1.insert(make_pair<int,string>(4,"d"));

5、查询和修改数据时要使用跌代器

下面举个例子，把它弄明白了就差不多了。

程序要求用户输入一行文字，按回车结束一行后输出当前这一行中所有单词及单词出现的次数，是不是很简单？

#include "iostream"
#include "map"
#include "string"
#include "sstream"
using namespace std;
int main(int argc, char *argv[])
{
	string input;
	string word;
	map<string,int> wordmap;
	while(getline(cin,input))
	{
		istringstream line(input);
		string word;
		while(line>>word)
		{
			map<string,int>::iterator i=wordmap.find(word);
			if(i==wordmap.end())
			{
				wordmap.insert(pair<string,int>(word,1));
			}
			else
			{
				wordmap[word]++;
			}
		}
		for(map<string,int>::iterator i=wordmap.begin();i!=wordmap.end();i++)
		{
			string times = (i->second>1)?" times!":" time!";
			cout<<"the word:"<<i->first<<" has appeared ";
			cout<<i->second;
			cout<<times<<endl;
		}
		wordmap.clear();
	}
	return 0;
}

像map这种键值对容器是很有用的，大家根据上面这个例子体会一下吧。