STL set multiset map multimap unordered_set unordered_map example
I decide to write to my blogs in English. When I meet something hard to depict, I'll add some Chinese necessarily.
The differences between these containers are :
- The keys of set and map are unique, but they could be multiple for multiset and multimap.
- Unordered_set and unordered_map are implemented by hash map, but the above 4 containers are implemented by Red-Black tree. They could have been named as hash_map, however, these names seem to have be used by other standards. So this ugly name ‘unordered’ is adopted in contrast to the attribute 'ordered' of the above 4 containers.
The following is the code:
#include<map>
#include<stdio.h>
#include<unordered_map>
#include<algorithm>
//#include<unordered_multimap> //there isn't such a library
#include<string>
#include<iostream>
using namespace std;
int main()
{
unordered_multimap<int, string> mapStudent1;
mapStudent1.insert(pair<int, string>(1, "student_one"));
mapStudent1.insert(pair<int, string>(2, "student_two"));
mapStudent1.insert(unordered_multimap<int, string>::value_type (2, "student_two")); //这样插入也可以，但是注意key是Unique的
mapStudent1.insert(make_pair<int, string>(3, "student_three"));
mapStudent1.insert(make_pair<int, string>(3, "student_three"));
//mapStudent.emplace(5,"student_five"); //Have to add the command '-std=c++11' for compiler
unordered_multimap<int, string>::iterator iter1;
for(iter1 = mapStudent1.begin(); iter1 != mapStudent1.end(); iter1++)
{
cout<<iter1->first<<" "<<iter1->second<<endl;
}
printf("-------------------------------\n\n");
map<int, string> mapStudent2;
mapStudent2.insert(pair<int, string>(1, "student_one"));
mapStudent2.insert(pair<int, string>(2, "student_two"));
mapStudent2.insert(map<int, string>::value_type (2, "student_two")); //这样插入也可以，但是注意key是Unique的
mapStudent2.insert(pair<int, string>(3, "student_three"));
mapStudent2.insert(pair<int, string>(3, "student_three"));
mapStudent2[4]="hello"; //利用数组插入同样可以，但是效率比较低
//mapStudent.emplace(5,"student_five"); //Have to add the command '-std=c++11' for compiler
map<int, string>::iterator iter2;
for(iter2 = mapStudent2.begin(); iter2 != mapStudent2.end(); iter2++)
{
cout<<iter2->first<<" "<<iter2->second<<endl;
}
printf("-------------------------------\n\n");
std::unordered_multimap<std::string,std::string> myumm = {
{"orange","FL"},
{"strawberry","LA"},
{"strawberry","OK"},
{"pumpkin","NH"} };
for (auto& x: {"orange","lemon","strawberry"}) {
std::cout << x << ": " << myumm.count(x) << " entries.\n";
}
printf("-------------------------------\n\n");
typedef std::unordered_multimap<std::string,std::string> stringmap;
stringmap myumm1 = {
{"orange","FL"},
{"strawberry","LA"},
{"pumpkin","NH"},
{"strawberry","OK"}
};
cout<<"All entries are:"<<endl;
stringmap::iterator iter3;
for(iter3 = myumm1.begin(); iter3 != myumm1.end(); iter3++)
{
cout<<iter3->first<<" "<<iter3->second<<endl;
}
std::cout << "Entries with strawberry:";
auto range = myumm1.equal_range("strawberry");
for_each (
range.first,
range.second,
[](stringmap::value_type& x){std::cout << " " << x.second;}
);
return 0;
}