C++ unordered_multimap empty()用法及代码示例

unordered_multimap::empty()是C++ STL中的内置函数，该函数返回布尔值。如果unordered_multimap容器为空，则返回true。否则，它返回false。

用法:

unordered_multimap_name.empty()

参数：该函数不接受任何参数。

返回值：它返回一个布尔值，该值指示unordered_multimap是否为空。

以下示例程序旨在说明上述函数：

示例1:

// C++ program to illustrate the 
// unordered_multimap::empty() function 
#include <iostream> 
#include <unordered_map> 
using namespace std; 
  
int main() 
{ 
  
    // declaration 
    unordered_multimap<int, int> sample; 
  
    // inserts key and element 
    sample.insert({ 1, 2 }); 
    sample.insert({ 1, 2 }); 
    sample.insert({ 2, 3 }); 
    sample.insert({ 3, 4 }); 
    sample.insert({ 5, 6 }); 
  
    // if not empty then print the elements 
    if (sample.empty() == false) { 
        cout << "Key and Elements: "; 
  
        for (auto it = sample.begin(); it != sample.end(); it++) { 
            cout << "{" << it->first << ":" << it->second << "} "; 
        } 
    } 
  
    // container is erased completely 
    sample.clear(); 
  
    if (sample.empty() == true) 
        cout << "\nContainer is empty"; 
  
    return 0; 
}

输出：

Key and Elements: {5:6} {3:4} {2:3} {1:2} {1:2} 
Container is empty

示例2:

// C++ program to illustrate the 
// unordered_multimap::empty() 
#include <iostream> 
#include <unordered_map> 
using namespace std; 
  
int main() 
{ 
  
    // declaration 
    unordered_multimap<char, char> sample; 
  
    // inserts element 
    sample.insert({ 'a', 'b' }); 
    sample.insert({ 'a', 'b' }); 
    sample.insert({ 'g', 'd' }); 
    sample.insert({ 'r', 'e' }); 
    sample.insert({ 'g', 'd' }); 
  
    // if not empty then print the elements 
    if (sample.empty() == false) { 
        cout << "Key and elements: "; 
  
        for (auto it = sample.begin(); it != sample.end(); it++) { 
            cout << "{" << it->first << ":" << it->second << "} "; 
        } 
    } 
  
    // container is erased completely 
    sample.clear(); 
  
    if (sample.empty() == true) 
        cout << "\nContainer is empty"; 
  
    return 0; 
}

输出：

Key and elements: {r:e} {g:d} {g:d} {a:b} {a:b} 
Container is empty

相关用法

注：本文由纯净天空筛选整理自gopaldave大神的英文原创作品 unordered_multimap empty() function in C++ STL。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。