在C++ STL中的unordered_map hash_function()函数

unordered_map::hash_function()是C++ STL中的内置函数，用于获取哈希函数。此哈希函数是一个一元函数，只接受一个参数，并根据它返回一个唯一的size_t类型值。

语法：

unordered_map_name.hash_function()

参数：该函数不接受任何参数。

返回值：该函数返回哈希函数。

时间复杂度：该函数的时间复杂度为O(1)。

下面的程序演示了unordered_map::hash_function()函数。

例子1

// C++ program to illustrate the
// unordered_map::hash_function()

#include <bits/stdc++.h>
using namespace std;

int main()
{

    // declaration
    unordered_map<string, string> sample;

    // inserts key and elements
    sample.insert({ "Ankit", "MNNIT" });
    sample.insert({ "Ram", "MNNIT" });
    sample.insert({ "Manoj", "Trichy" });
    sample.insert({ "geeks", "geeks" });

    // use of hash_function
    unordered_map<string, string>::hasher fn
        = sample.hash_function();

    cout << fn("geeks") << endl;

    // print the key and elements

    cout << "Key and Elements: ";
    for (auto it = sample.begin(); it != sample.end(); it++) {
        cout << "\n{" << it->first << ":"
            << it->second << "}, ";
    }
    return 0;
}

15276750567035005396
Key and Elements: 
{geeks:geeks}, 
{Manoj:Trichy}, 
{Ankit:MNNIT}, 
{Ram:MNNIT},

例子2

// C++ program to illustrate the
// unordered_map::hash_function()

#include <bits/stdc++.h>
using namespace std;

int main()
{

    // declaration
    unordered_map<int, int> sample;

    // inserts key and elements
    sample.insert({ 1, 5 });
    sample.insert({ 2, 6 });
    sample.insert({ 3, 6 });
    sample.insert({ 4, 7 });

    // use of hash_function
    unordered_map<int, int>::hasher fn
        = sample.hash_function();

    cout << fn(4) << endl;

    // print the key and elements

    cout << "Key and Elements: ";
    for (auto it = sample.begin(); it != sample.end(); it++) {
        cout << "\n{" << it->first << ":"
            << it->second << "}, ";
    }
    return 0;
}

4
Key and Elements: 
{4:7}, 
{3:6}, 
{1:5}, 
{2:6},