std::basic_string<CharT,Traits,Allocator>::capacity

 

C++

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以空字符结尾的字符串

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basic_string

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std::basic_string

成员函数 basic_string::basic_string basic_string::~basic_string basic_string::operator= basic_string::assign basic_string::assign_range (C++23) basic_string::get_allocator 元素访问 basic_string::at basic_string::operator[] basic_string::front (DR*) basic_string::back (DR*) basic_string::data basic_string::c_str basic_string::operator  basic_string_view (C++17) 迭代器 basic_string::beginbasic_string::cbegin (C++11) basic_string::endbasic_string::cend (C++11) basic_string::rbeginbasic_string::crbegin (C++11) basic_string::rendbasic_string::crend (C++11) 容量 basic_string::empty basic_string::sizebasic_string::length basic_string::max_size basic_string::reserve basic_string::capacity basic_string::shrink_to_fit (DR*) 修改器 basic_string::clear basic_string::insert basic_string::insert_range (C++23) basic_string::erase basic_string::push_back basic_string::pop_back (DR*) basic_string::append basic_string::append_range (C++23) basic_string::operator+= basic_string::replace basic_string::replace_with_range (C++23) basic_string::copy basic_string::resize basic_string::resize_and_overwrite (C++23)   basic_string::swap

搜索 basic_string::find basic_string::rfind basic_string::find_first_of basic_string::find_first_not_of basic_string::find_last_of basic_string::find_last_not_of 操作 basic_string::compare basic_string::starts_with (C++20) basic_string::ends_with (C++20) basic_string::contains (C++23) basic_string::substr 常量 basic_string::npos 非成员函数 operator+ swap(std::basic_string) erase(std::basic_string)erase_if(std::basic_string) (C++20)(C++20) I/O operator<<operator>> getline 比较 operator==operator!=operator<operator>operator<=operator>=operator<=> (直到 C++20)(直到 C++20)(直到 C++20)(直到 C++20)(直到 C++20)(C++20) 数值转换 stoistolstoll (C++11)(C++11)(C++11) stoulstoull (C++11)(C++11) stofstodstold (C++11)(C++11)(C++11) to_string (C++11) to_wstring (C++11) 字面量 operator""s (C++14) 辅助类 hash<std::basic_string> (C++11) 推导指南 (C++17)

 

size_type capacity() const;		(从 C++11 开始为 noexcept) (从 C++20 开始为 constexpr)

返回字符串当前分配的空间字符数。

参数

(无)

返回值

当前分配的存储空间的容量，即用于存储元素的可用空间。

复杂度

常数。

注释

从分配器获得但不可用于存储任何元素的内存位置不计入分配的存储空间。请注意，空终止符不是 std::basic_string 的元素。

示例

运行此代码

#include <iomanip>
#include <iostream>
#include <string>
 
void show_capacity(std::string const& s)
{
    std::cout << std::quoted(s) << " has capacity " << s.capacity() << ".\n";
}
 
int main()
{
    std::string s{"Exemplar"};
    show_capacity(s);
 
    s += " is an example string.";
    show_capacity(s);
 
    s.clear();
    show_capacity(s);
 
    std::cout << "\nDemonstrate the capacity's growth policy."
                 "\nSize:  Capacity:  Ratio:\n" << std::left;
 
    std::string g;
    auto old_cap{g.capacity()};
 
    for (int mark{}; mark != 5; ++mark)
    {
        while (old_cap == g.capacity())
            g.push_back('.');
 
        std::cout << std::setw( 7) << g.size()
                  << std::setw(11) << g.capacity()
                  << std::setw(10) << g.capacity() / static_cast<float>(old_cap) << '\n';
 
        old_cap = g.capacity();
    }
}

可能的输出

"Exemplar" has capacity 15.
"Exemplar is an example string." has capacity 30.
"" has capacity 30.
 
Demonstrate the capacity's growth policy.
Size:  Capacity:  Ratio:
16     30         2
31     60         2
61     120        2
121    240        2
241    480        2

另请参阅

sizelength	返回字符数量 (公共成员函数)
reserve	保留存储空间 (公共成员函数)