map::find

Artikel
07/29/2015

Returns an iterator that refers to the location of an element in a map that has a key equivalent to a specified key.

iterator find(const Key& key);

const_iterator find(const Key& key) const;

Parameters

key
The key value to be matched by the sort key of an element from the map being searched.

Return Value

An iterator that refers to the location of an element with a specified key, or the location succeeding the last element in the map (map::end()) if no match is found for the key.

Remarks

The member function returns an iterator that refers to an element in the map whose sort key is equivalent to the argument key under a binary predicate that induces an ordering based on a less than comparability relation.

If the return value of find is assigned to a const_iterator, the map object cannot be modified. If the return value of find is assigned to an iterator, the map object can be modified

Example

// compile with: /EHsc /W4 /MTd
#include <map>
#include <iostream>
#include <vector>
#include <string>
#include <utility>  // make_pair()

using namespace std;

template <typename A, typename B> void print_elem(const pair<A, B>& p) {
    cout << "(" << p.first << ", " << p.second << ") ";
}

template <typename T> void print_collection(const T& t) {
    cout << t.size() << " elements: ";

    for (const auto& p : t) {
        print_elem(p);
    }
    cout << endl;
}

template <typename C, class T> void findit(const C& c, T val) {
    cout << "Trying find() on value " << val << endl;
    auto result = c.find(val);
    if (result != c.end()) {
        cout << "Element found: "; print_elem(*result); cout << endl;
    } else {
        cout << "Element not found." << endl;
    }
}

int main()
{
    map<int, string> m1({ { 40, "Zr" }, { 45, "Rh" } });
    cout << "The starting map m1 is (key, value):" << endl;
    print_collection(m1);

    vector<pair<int, string>> v;
    v.push_back(make_pair(43, "Tc"));
    v.push_back(make_pair(41, "Nb"));
    v.push_back(make_pair(46, "Pd"));
    v.push_back(make_pair(42, "Mo"));
    v.push_back(make_pair(44, "Ru"));
    v.push_back(make_pair(44, "Ru")); // attempt a duplicate

    cout << "Inserting the following vector data into m1:" << endl;
    print_collection(v);

    m1.insert(v.begin(), v.end());

    cout << "The modified map m1 is (key, value):" << endl;
    print_collection(m1);
    cout << endl;
    findit(m1, 45);
    findit(m1, 6);
}

Output

The starting map m1 is (key, value):
2 elements: (40, Zr) (45, Rh)
Inserting the following vector data into m1:
6 elements: (43, Tc) (41, Nb) (46, Pd) (42, Mo) (44, Ru) (44, Ru)
The modified map m1 is (key, value):
7 elements: (40, Zr) (41, Nb) (42, Mo) (43, Tc) (44, Ru) (45, Rh) (46, Pd)

Trying find() on value 45
Element found: (45, Rh)
Trying find() on value 6
Element not found.

Requirements

Header: <map>

Namespace: std

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