C++ STL 中的 multimap::emplace_hint() 函数

2024年8月28日 | 阅读 4 分钟

众所周知，C++ 编程语言有许多内置函数，可以帮助我们避免编写冗长的代码。其中一个函数就是 multimap emplace_hint 函数，它存在于 C++ 编程语言丰富的库——标准模板库 (STL) 中。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。带提示的 emplace_hint 比普通的 emplace 查找速度快得多。它会根据提示插入键元素，并且该提示不会影响要插入的位置。

C++ 代码中的 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 initializer 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 that 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;

	
return 0;
    
}

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 assign from gquiz1 is : 
	KEY	ELEMENT
	1	40
	2	30
	3	60
	4	50
	5	10
	6	50
	6	10

C++ STL 中的 multimap::emplace_hint() 函数

语法

C++ 代码

// Here we are writing down the C++ programming language code to 
// demonstrate
// the concept of multimap::emplace_hint() function in the 
// 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 initializer container 
	// which will help us with creating a multimap using C++ STL
	multimap<int, int> mp;

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

	mp.emplace_hint(mp.begin(), 12, 230); // this is faster
	mp.emplace_hint(mp.begin(), 14, 440); // this is faster
	mp.emplace_hint(mp.begin(), 42, 960); // this is slower
	mp.emplace_hint(mp.begin(), 32, 620); // this is slower
	mp.emplace_hint(mp.begin(), 31, 540); // this is faster
	mp.emplace_hint(mp.begin(), 17, 150); // this is faster

    // elements that we are going to display on the Output screen are
	cout << "\nThe multimap is : \n";
	cout << "KEY\tELEMENT\n";
	
	// here we are writing the for loop, which contains the auto code
	// functionality containing the find() function at different positions 
	for (auto itr = mp.begin(); itr != mp.end(); itr++)
		cout << itr->first << "\t" << itr->second << endl;

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

输出

The multimap is : 
KEY	ELEMENT
12	230
14	440
17	150
31	540
32	620
42	960

下一主题C++ STL 中的 Multimap find()

C++ STL 中的 multimap::emplace_hint() 函数

C++ 代码中的 Multimap

C++ STL 中的 multimap::emplace_hint() 函数

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C++ STL 中的 multimap::emplace_hint() 函数

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C++ STL 中的 multimap::emplace_hint() 函数

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