std::map::empty

 

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std::map

成员函数 Original: Member functions The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

map::map

map::~map

map::operator=

map::get_allocator

元素的访问 Original: Element access The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

map::at

map::operator[]

迭代器 Original: Iterators The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

map::begin map::cbegin （C++11）

map::end map::cend （C++11）

map::rbegin map::crbegin （C++11）

map::rend map::crend （C++11）

容量 Original: Capacity The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

map::empty

map::size

map::max_size

修饰符 Original: Modifiers The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

map::clear

map::insert

map::emplace （C++11）

map::emplace_hint （C++11）

map::erase

map::swap

查找 Original: Lookup The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

map::count

map::find

map::equal_range

map::lower_bound

map::upper_bound

观察员 Original: Observers The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

map::key_comp

map::value_comp

 

bool empty() const;

检查，如果容器有任何元素，即是否begin() == end().

Original:

Checks if the container has no elements, i.e. whether begin() == end().

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参数

（无）

Original:

(none)

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返回值

true如果容器是空的，false其他方式

Original:

true if the container is empty, false otherwise

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例外

noexcept specification:  

noexcept

  （C++11 起）

复杂性

常数

Original:

Constant

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为例

下面的代码使用empty检查，如果std::map<int>包含任何元素

Original:

The following code uses empty to check if a std::map<int> contains any elements:

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#include <map>
#include <iostream>
 
int main()
{
    std::map<int> numbers;
    std::cout << "Initially, numbers.empty(): " << numbers.empty() << '\n';
 
    numbers.push_back(42);
    numbers.push_back(13317);
    std::cout << "After adding elements, numbers.empty(): " << numbers.empty() << '\n';
}

Output:

Initially, numbers.empty(): 1
After adding elements, numbers.empty(): 0

See also

size	返回的元素数 Original: returns the number of elements The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. （公共成员函数）