std::vector<T,Allocator>::capacity

 

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std::vector

成員型別
成員函式
vector::vector vector::~vector vector::operator= vector::assign vector::assign_range (C++23)   vector::get_allocator 元素訪問 vector::operator[] vector::at vector::data vector::front vector::back 迭代器 vector::beginvector::cbegin (C++11) vector::endvector::cend (C++11) vector::rbeginvector::crbegin (C++11) vector::rendvector::crend (C++11)	容量 vector::empty vector::size vector::max_size vector::reserve vector::capacity vector::shrink_to_fit (DR*) 修改器 vector::clear vector::erase vector::insert vector::insert_range (C++23) vector::append_range (C++23) vector::emplace (C++11) vector::emplace_back (C++11) vector::push_back vector::pop_back vector::resize vector::swap
非成員函式
operator==operator<=> (C++20 起) swap(std::vector) erase(std::vector)erase_if(std::vector) (C++20)(C++20)	operator!=operator<operator>operator<=operator>= (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)
推導指南(C++17)

 

size_type capacity() const;		(C++11 起無異常丟擲) (C++20 起為 constexpr)

返回容器當前已分配空間所能容納的元素數量。

引數

(無)

返回值

當前已分配儲存的容量。

複雜度

常數時間。

示例

執行此程式碼

#include <iomanip>
#include <iostream>
#include <vector>
 
int main()
{
    int sz = 100;
    std::vector<int> v;
 
    auto cap = v.capacity();
    std::cout << "Initial size: " << v.size() << ", capacity: " << cap << '\n';
 
    std::cout << "\nDemonstrate the capacity's growth policy."
                 "\nSize:  Capacity:  Ratio:\n" << std::left;
    while (sz-- > 0)
    {
        v.push_back(sz);
        if (cap != v.capacity())
        {
            std::cout << std::setw( 7) << v.size()
                      << std::setw(11) << v.capacity()
                      << std::setw(10) << v.capacity() / static_cast<float>(cap) << '\n';
            cap = v.capacity();
        }
    }
 
    std::cout << "\nFinal size: " << v.size() << ", capacity: " << v.capacity() << '\n';
}

可能的輸出

Initial size: 0, capacity: 0
 
Demonstrate the capacity's growth policy.
Size:  Capacity:  Ratio:
1      1          inf
2      2          2
3      4          2
5      8          2
9      16         2
17     32         2
33     64         2
65     128        2
 
Final size: 100, capacity: 128

參閱

size	返回元素數量 (public member function)
reserve	預留儲存空間 (public member function)