👀 Views: 82 💬 Answers: 1 📅 Created: 2025-06-13

c++ std-vector c++20 cpp

I've hit a wall trying to I'm relatively new to this, so bear with me..... I'm working with an scenario where my `std::vector` is not resizing as expected when I use `emplace_back` to add elements, particularly when I attempt to add a large number of complex objects. The code is running in a C++20 environment, and I'm using Visual Studio 2022. Here’s a simplified version of my code: ```cpp #include <iostream> #include <vector> class MyClass { public: MyClass(int id) : id(id) { std::cout << "Constructing MyClass " << id << '\n'; } ~MyClass() { std::cout << "Destructing MyClass " << id << '\n'; } private: int id; }; int main() { std::vector<MyClass> myVector; for (int i = 0; i < 10000; ++i) { myVector.emplace_back(i); } std::cout << "Vector size: " << myVector.size() << '\n'; return 0; } ``` When I run this code, I expect to see "Vector size: 10000", but instead, I get an unexpected performance hit, and in some cases, I observe that the vector seems to be reaching its capacity limit earlier than anticipated. I also see several "Destructing MyClass" messages appearing, which suggests that some objects are being destructed prematurely. I’ve tried preallocating the vector with `myVector.reserve(10000);` before the loop, and that improved the performance slightly, but I still ended up with fewer elements than expected. I suspect it could be related to the way `std::vector` handles memory allocation or potential issues with the move semantics in my `MyClass` implementation. Could anyone shed light on why `std::vector` might be failing to resize properly in this case or if there are any specific configurations in C++20 that might affect its behavior? Any insights or suggestions for troubleshooting would be greatly appreciated. I'm working with Cpp in a Docker container on Linux. This issue appeared after updating to Cpp latest. What's the best practice here?