advanced patterns with std::vector's resize() and custom object that contains std::unique_ptr in C++
I'm converting an old project and I'm stuck trying to Hey everyone, I'm running into an issue that's driving me crazy... I've been banging my head against this for hours. I've looked through the documentation and I'm still confused about I'm working with an scenario with resizing a `std::vector` that holds custom objects containing `std::unique_ptr`... My custom class has a destructor that prints a message when it gets destroyed. However, when I call `resize()` on the vector, it seems like the destructors for some of the objects are not being called, leading to unexpected behavior. Here’s a simplified version of my code: ```cpp #include <iostream> #include <vector> #include <memory> class MyObject { public: MyObject() { std::cout << "MyObject created\n"; } ~MyObject() { std::cout << "MyObject destroyed\n"; } }; int main() { std::vector<std::unique_ptr<MyObject>> vec; vec.push_back(std::make_unique<MyObject>()); vec.push_back(std::make_unique<MyObject>()); vec.resize(5); // This line causes issues return 0; } ``` When I run this code, I expect to see destruction messages for all the objects that were previously in the vector when it is resized. However, it seems like the two original `MyObject` instances are not being destroyed when I call `resize(5)`, which is leading to some memory that I expect to be released not getting freed. The output is: ``` MyObject created MyObject created ``` Am I missing something about how `std::unique_ptr` and `std::vector` interact during a `resize()` operation? I would appreciate any insights on this behavior or best practices to avoid similar issues in the future. I'm compiling this with g++ 11.1.0 on Linux. Any help would be greatly appreciated! Any ideas what could be causing this? This is my first time working with C++ 3.10. Thanks, I really appreciate it!