Editing Openai/6957acb5-7d70-8002-a8e3-6e77a3f0799e


{{DISPLAYTITLE:Vector Destructor Behavior}}

''This conversation was exported from ChatGPT''<ref>{{cite web|title=Vector Destructor Behavior|url=https://chatgpt.com/share/6957acb5-7d70-8002-a8e3-6e77a3f0799e|publisher=ChatGPT|access-date=2026-01-03}}</ref>

== gpt-5-2-thinking ==
=== User: what will this program print? ===
what will this program print? I'm building with g++.

#include <vector>
#include <iostream>

struct A{
    int i{};

    A(int i_)
    :i(i_)
    {}
    ~A() {
        std::cout << "Destruct " << i << std::endl;
    }
};

int main() {
    std::vector<A> vec;
    vec.reserve(5);

    vec.emplace_back(1);
    vec.emplace_back(2);
}

=== Assistant: With vec.reserve5 there’s no reallocation, so no extra moves/copies/destructions happen during the emplacebacks. ===
With vec.reserve(5) there’s no reallocation, so no extra moves/copies/destructions happen during the emplace_backs. The only destructors run are when vec is destroyed at the end of main.

With g++ (libstdc++), the vector destructor destroys elements from begin() to end(), so you’ll get:

<syntaxhighlight lang="text">Destruct 1
Destruct 2

</syntaxhighlight>

The C++ standard doesn’t require a specific destruction order for std::vector’s elements, so a different standard library could legally print the opposite order. en.cppreference.com<ref>{{cite web|title=en.cppreference.com|url=https://en.cppreference.com/w/cpp/container/vector/~vector.html|publisher=en.cppreference.com|access-date=2026-01-03}}</ref>

== References ==
<references />


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