C++ STL 中的 multimap find()

28 Aug 2024 | 5 分钟阅读

众所周知，C++ 编程语言有许多内置函数，可帮助我们避免编写冗长的代码行。其中一个函数是 C++ 编程语言丰富库（标准模板库 (STL)）中提供的 multimap find 函数。它将帮助我们返回一个迭代器，该迭代器引用或指向我们创建的长或短 multimap 中包含数据遍历的键的位置。如果您有了解所有基本数据值的不同目标，那么您可以参考 C++ 编程语言丰富库（标准模板库 (STL)）中可用的 equal range 函数。

C++ 中的 Multimap

// Here we are writing down the C++ programming language code to 
// demonstrate
// the concept of multimap find() in C++ STL(Standard Template Library)

#include <iostream>
#include <iterator>
#include <map>

using namespace std;
// The main driver code functionality starts from here!
int main()
{
    // Here, we are trying to create an initialiser container 
	// which will help us with creating a multimap using C++ STL
	multimap<int, int> gquiz1;

     // these insert functions which we have written below help us
	// with creating a multimap holding the values inserted below!

	gquiz1.insert(pair<int, int>(1, 40));
	gquiz1.insert(pair<int, int>(2, 30));
	gquiz1.insert(pair<int, int>(3, 60));
	gquiz1.insert(pair<int, int>(6, 50));
	gquiz1.insert(pair<int, int>(6, 10));

	 // elements which we are going to display on the Output screen are
	multimap<int, int>::iterator itr;
	cout << "\nThe multimap gquiz1 is : \n";
	cout << "\tKEY\tELEMENT\n";
	// here we are writing the for loop, which contains the auto code
	// functionality containing the find() function at different positions
	for (itr = gquiz1.begin(); itr != gquiz1.end(); ++itr) {
		cout << '\t' << itr->first
			<< '\t' << itr->second << '\n';
	}
	cout << endl;

	// here, we are trying to add elements randomly,
	// as it helps us to check the sorted keys property in C++ STL
	gquiz1.insert(pair<int, int>(4, 50));
	gquiz1.insert(pair<int, int>(5, 10));

	// the below code helps us with printing multimap gquiz1 again

	cout << "\nmultimap quiz1 after"
		<< " adding the extra elements is : \n";
	cout << "\tkey\telement\n";
	for (itr = gquiz1.begin(); itr != gquiz1.end(); ++itr) {
		cout << '\t' << itr->first
			<< '\t' << itr->second << '\n';
	}
	cout << endl;

	// the below code snippet below assigning the elements from quiz1 to quiz2
	multimap<int, int> gquiz2(gquiz1.begin(),
							gquiz1.end());

// the below code snippet prints all the elements of the multimap gquiz2
	cout << "\nThe multimap gquiz2 after"
		<< " assign from gquiz1 is : \n";
	cout << "\tKEY\tELEMENT\n";
	for (itr = gquiz2.begin(); itr != gquiz2.end(); ++itr) {
		cout << '\t' << itr->first
			<< '\t' << itr->second << '\n';
	}
	cout << endl;

	// here, we are trying to remove all elements up to
	// key with the value 3 in quiz2
	cout << "\n the quiz2 after the removal of"
		<< " elements less than key = 3 : \n";
	cout << "\t key \t element \n";
	gquiz2.erase(gquiz2.begin(), gquiz2.find(3));
	for (itr = gquiz2.begin(); itr != gquiz2.end(); ++itr) {
		cout << '\t' << itr->first
			<< '\t' << itr->second << '\n';
	}

	// the below code helps us with removing all the elements with key = 4
	int num;
	num = gquiz2.erase(4);
	cout << "\n quiz 2.erase(4) : ";
	cout << num << " removed \n";
	cout << "\tkey\telement\n";
	for (itr = gquiz2.begin(); itr != gquiz2.end(); ++itr) {
		cout << '\t' << itr->first
			<< '\t' << itr->second << '\n';
	}

// new line printing statement the endl statement
	cout << endl;

	// the lower and upper bounds of the much awaited 
	// for multimap gquiz1 key = 5
	cout << "the quiz1.lower bound (5) : "
		<< "\tkey = ";
	cout << gquiz1.lower_bound(5)->first << '\t';
	cout << "\telement = "
		<< gquiz1.lower_bound(5)->second
		<< endl;
	cout << "the quiz1.upper bound (5): "
		<< "\tKEY = ";
	cout << gquiz1.upper_bound(5)->first << '\t';
	cout << "\telement = "
		<< gquiz1.upper_bound(5)->second
		<< endl;

	return 0;
	// The main driver code functionality ends from here!
}

输出

The multimap gquiz1 is : 
	KEY	ELEMENT
	1	40
	2	30
3	60
	6	50
	6	10


Multimap quiz1 after adding the extra elements is : 
	key	element
	1	40
	2	30
	3	60
	4	50
	5	10
	6	50
	6	10


The multimap gquiz2 after assignment from gquiz1 is : 
	KEY	ELEMENT
	1	40
	2	30
	3	60
	4	50
	5	10
	6	50
	6	10


 quiz2 after the removal of elements less than key = 3 : 
	 key 	 element 
	3	60
	4	50
	5	10
	6	50
	6	10

 quiz 2.erase(4) : 1 removed 
	key	element
	3	60
	5	10
	6	50
	6	10

the quiz1.lower bound (5) : 	key = 5		element = 10
the quiz1.upper bound (5) : 	KEY = 6		element = 50

C++ STL 中的 multimap find()

语法

iterator multimap_name.find(key)
constant iterator multimap_name.find(key)

C++ 代码

// Here we are writing down the C++ programming language code to demonstrate
// the concept of multimap find() in C++ STL(Standard Template Library)
#include <bits/stdc++.h>
using namespace std;
// The main driver code functionality starts from here!
int main()
{

	// Here, we are trying to create an initialiser container 
	// which will help us with creating a multimap using C++ STL
	multimap<int, int> mp;

	// these insert functions which we have written below help us
	// with creating a multimap holding the values inserted below!
	mp.insert({ 12, 130 });
	mp.insert({ 11, 140 });
	mp.insert({ 12, 160 });
	mp.insert({ 31, 210 });
	mp.insert({ 11, 501 });
	mp.insert({ 14, 510 });

    // elements which we are going to display on the Output screen are
	cout << "The elements from position 3 in multimap are : \n";
	cout << "Key\telements : \n";

	// here we are writing the for loop, which contains the auto code
	// functionality containing the find() function at position 3
	for (auto itr = mp.find(31); itr != mp.end(); itr++)
		cout << itr->first
			<< '\t' << itr->second << '\n';

	return 0;
	// The main driver code functionality ends from here!
}

输出

The elements from position 3 in multimap are : 
Key	elements : 
31	210

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