std::vector::shrink_to_fit(3)

💅 std::vector::shrink_to_fit(3) — the C++ Standard Library, bestie

okay so we're in the C++ Standard Library today (std::vector::shrink_to_fit), and this one's a little icon of "please free my memory... if you feel like it." ✨

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🌸 NAME

std::vector::shrink_to_fit — literally the same thing as std::vector::shrink_to_fit, no notes 💅

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✨ Synopsis

void shrink_to_fit();  (constexpr since C++20)

Requests the removal of unused capacity. 🎀

It's a non-binding request to reduce capacity() to size(). Whether the request actually gets fulfilled depends on the implementation — so like, you asked nicely, but nobody promised you anything, yk? 🙈

If reallocation occurs, all iterators (including the end() iterator) and all references to the elements are invalidated. If no reallocation occurs, no iterators or references are invalidated. 👑

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🦋 Parameters

(none)

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💜 Type requirements

• T must meet the requirements of MoveInsertable into *this. (since C++11)

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🌈 Return value

(none)

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⭐ Complexity

At most linear in the size of the container.

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🔥 Exceptions

(since C++11)

If an exception is thrown other than by the move constructor of a non-CopyInsertable T, there are no effects. 🫶

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🍓 Notes

In libstdc++, shrink_to_fit() is not available in C++98 mode. periodt.

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💖 Example

// Run this code

#include <iostream>
#include <vector>

int main()
{
    std::vector<int> v;
    std::cout << "Default-constructed capacity is " << v.capacity() <<
'\n';
    v.resize(100);
    std::cout << "Capacity of a 100-element vector is " << v.capacity()
<< '\n';
    v.resize(50);
    std::cout << "Capacity after resize(50) is " << v.capacity() <<
'\n';
    v.shrink_to_fit();
    std::cout << "Capacity after shrink_to_fit() is " << v.capacity() <<
'\n';
    v.clear();
    std::cout << "Capacity after clear() is " << v.capacity() << '\n';
    v.shrink_to_fit();
    std::cout << "Capacity after shrink_to_fit() is " << v.capacity() <<
'\n';
    for (int i = 1000; i < 1300; ++i)
        v.push_back(i);
    std::cout << "Capacity after adding 300 elements is " <<
v.capacity() << '\n';
    v.shrink_to_fit();
    std::cout << "Capacity after shrink_to_fit() is " << v.capacity() <<
'\n';
}

🎀 Possible output

Default-constructed capacity is 0
Capacity of a 100-element vector is 100
Capacity after resize(50) is 100
Capacity after shrink_to_fit() is 50
Capacity after clear() is 50
Capacity after shrink_to_fit() is 0
Capacity after adding 300 elements is 512
Capacity after shrink_to_fit() is 300

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👑 Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards. (yes, they went back and edited history, main character energy fr fr)

• LWG 755, applied to C++98 — behavior as published: std::vector lacked explicit shrink-to-fit operations. Correct behavior: provided. 💀
• LWG 2033, applied to C++11 — behavior as published: 1. T was not required to be MoveInsertable 2. the complexity requirement was missing. Correct behavior: 1. required 2. added. 🔥

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🌸 See also

• size — returns the number of elements (public member function)
• capacity — returns the number of elements that can be held in currently allocated storage (public member function)

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okay that's the whole page, bestie, you ate that 🫶 go shrink some capacity (or don't, it's non-binding, live your truth) 💅

source/version: http://cppreference.com — dated 2024.06.10 — std::vector::shrink_to_fit(3) signing off 🧚💖