Getting the value of a multimap in C++

Question

我想知道如何在C ++中检索多地图的值

Answer 1

Multimap has internal structure represented as std::pair<T_k, T_v> . It has first, second members. first is the key and second is the value associated with the key.

#include <iostream>
#include <map>

using namespace std;

int main(){

        multimap<int,int> a;
        a.insert(pair<int,int> (1,2));
        a.insert(pair<int,int> (1,2));
        a.insert(pair<int,int> (1,4));
        for (multimap<int,int>::iterator it= a.begin(); it != a.end(); ++it) {
                cout << it->first << "\t" << it->second << endl ;
        }

        return 0;
}

Output :

1 2
1 2
1 4

Answer 2

To retrieve the value of a multimap you need to use its name.

So if you have a multimap called myMap , you can retrieve its value with the expression:

myMap

Once you have its value, you can copy it into another multimap, or you can call member functions on it to decompose its value into smaller logical subvalues.

---

To access a particular range of mapped values that correspond to aa given key (called myKey in this example), you can use:

myMap.equal_range(myKey)

This evaluates to a std::pair of iterator s (or const_iterators if myMap is const ), which delimit the range of key-value pairs with keys that are equivalent to myKey .

For example (assume that myMap is a map from T1 to T2, where T1 and T2 are not dependent types):

typedef std::multimap<T1, T2>::iterator iter;
for (std::pair<iter, iter> range(myMap.equal_range(myKey));
     range.first != range.second;
     ++range.first)
{
    //In each iteration range.first will refer to a different object
    //In each case, range.first->first will be equivalent to myKey
    //and range.first->second will be a value that range.first->first maps to.
}