map详解

一、clear(),empty(),size().insert(),begin(),end()

 clear() 清空迭代器 

begin() 返回指向第一个元素额迭代器 

end() 返回指向末尾元素的迭代器 

empty() 如果为空，返回 true 

size() 返回元素的数量 

insert(pair<keytype,valuetype> val)  插入 pair 类型元素，对 map 返回一个 pair，first 指向插入元素的迭代器， second 表示插入是否成功

insert(loc,pair<keytype, valuetype>val) 从 loc 寻找一个可以插入值为 value 的元素的位置并将其插入返回 map 

#include<iostream>#include<map>using namespace std;int main(){    map<int,char> mymap;    map<int,char>::iterator it;    mymap.insert(pair<int,char>(1,'a'));    mymap.insert(pair<int,char>(4,'b'));    pair<map<int,char>::iterator,bool> ret;    ret = mymap.insert ( pair<int,char>(4,'c'));    if (ret.second==false) {        cout << "element 'z' already existed";        cout << " with a value of " << ret.first->second <<endl;    }    cout<<"mymap1:"<<endl;    for(it=mymap.begin();it!=mymap.end();it++)        cout<<it->first<<" => "<<it->second<<endl;    mymap.insert(it, pair<char,int>(2,'c'));    mymap.insert(it, pair<char,int>(3,'d'));    cout<<"mymap2:"<<endl;    for(it=mymap.begin();it!=mymap.end();it++)        cout<<it->first<<" => "<<it->second<<endl;    cout<<"size:"<<mymap.size()<<endl;    mymap.clear();    if(mymap.empty())        cout<<"clear"<<endl;    return 0;}

代码运行如下：

二、rbegin(),rend()

rbegin() 返回逆向迭代器，指向链表末尾 

rend() 返回指向开头之前位置的迭代器 

#include<iostream>#include<map>using namespace std;int main(){    map<int,char> mymap;    map<int,char>::reverse_iterator its;    mymap[1] = 'a';    mymap[2] = 'b';    mymap[3] = 'c';    cout<<"mymap:"<<endl;    for(its=mymap.rbegin(); its!=mymap.rend(); ++its)            std::cout << its->first << " => " << its->second <<endl;    return 0;}

代码运行如下：

三、erase()

erase(loc) 删除 loc 所指元素

erase(start,end) 删除[start,end）之间的元素

erase(key_type key) 删除 key 值为 value 的元素，并返回 删除的个数

#include<iostream>#include<map>using namespace std;int main (){  map<int,char> mymap;  map<int,char>::iterator it;  map<int,char>::iterator its;  mymap[1]='a';  mymap[2]='b';  mymap[3]='c';  mymap[4]='d';  mymap[5]='e';  mymap[6]='f';  cout<<"first:"<<endl;  for(its=mymap.begin(); its!=mymap.end(); ++its)    cout << its->first << " => " << its->second <<endl;  it=mymap.find(2);  mymap.erase (it);  mymap.erase (3);  it=mymap.find (5);  cout<<"second:"<<endl;  for(its=mymap.begin(); its!=mymap.end(); ++its)    cout << its->first << " => " << its->second <<endl;  mymap.erase (it,mymap.end());  cout<<"3rd:"<<endl;  for(its=mymap.begin(); its!=mymap.end(); ++its)    cout << its->first << " => " << its->second <<endl;  return 0;}

代码运行如下：

四、find()

find(key_type key) 返回一个迭代器指向键值为 key 的元 素，未找到返回 end()

#include<iostream>#include<map>using namespace std;int main (){    map<int,char> mymap;    map<int,char>::iterator it;    mymap[1]='a';    mymap[2]='b';    mymap[3]='c';    mymap[4]='d';    it=mymap.find(2);    mymap.erase(it);    mymap.erase(mymap.find(4));    cout<< "mymap:" <<endl;    cout<< "1 => " << mymap.find(1)->second <<endl;    cout<< "3 => " << mymap.find(3)->second <<endl;  return 0;}

代码运行如下：

五、其他

lower_bound(key_type key) 返回一个迭代器指向>=key 的第一个元素

upper_bound(key_type key) 返回一个迭代器，指向>key 的第一个元素

#include<iostream>#include<map>using namespace std;int main (){    map<int,char> mymap;    map<int,char>::iterator itlow,itup,it;    mymap[1]='a';    mymap[2]='b';    mymap[3]='c';    mymap[4]='d';    mymap[5]='e';    itlow=mymap.lower_bound(2);    itup=mymap.upper_bound(4);    mymap.erase(itlow,itup);    cout<<"mymap:"<<endl;    for(it=mymap.begin(); it!=mymap.end(); ++it)        cout << it->first << " => " << it->second <<endl;    return 0;}

代码运行如下：

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