std::string shrink_to_fit() 方法

自 C++20 起

// Non const version only
constexpr void shrink_to_fit();

自 C++11 起

// Non const version only
void shrink_to_fit();

请求移除未使用的容量。
这是一个非绑定请求，用于将 capacity() 减少到 size()。
请求是否被满足取决于实现。

失效

如果发生重新分配，所有指针、引用和迭代器都将失效。

参数

(无)

返回值

(无)

复杂度

自 C++17 起

容器大小的线性复杂度 - O(size())。

C++17 之前

未指定。

异常

(无)

示例

Main.cpp

#include <iostream>
#include <string>
 
int main()
{
    std::string s;
    std::cout << "Size of std::string is " << sizeof s << " bytes\n"
        << "Default-constructed capacity is " << s.capacity() 
        << " and size is " << s.size() << '\n';
    for (int i=0; i<42; i++)
        s.append(" 42 ");
    std::cout << "Capacity after 42 appends is " << s.capacity() 
        << " and size is " << s.size() << '\n';
    s.clear();
    std::cout << "Capacity after clear() is " << s.capacity() 
        << " and size is " << s.size() << '\n';
    s.shrink_to_fit();
    std::cout << "Capacity after shrink_to_fit() is " << s.capacity() 
        << " and size is " << s.size() << '\n';
}

可能输出

GCC output:
Size of std::string is 32 bytes
Default-constructed capacity is 15 and size 0
Capacity after 42 appends is 240 and size 168
Capacity after clear() is 240 and size 0
Capacity after shrink_to_fit() is 15 and size 0
 
clang output (with -stdlib=libc++):
Size of std::string is 24 bytes
Default-constructed capacity is 22 and size is 0
Capacity after 42 appends is 191 and size is 168
Capacity after clear() is 191 and size is 0
Capacity after shrink_to_fit() is 22 and size is 0