👀 Views: 69 💬 Answers: 1 📅 Created: 2025-06-16

c++ stdvector emplace_back C++

I'm trying to figure out I'm collaborating on a project where I've tried everything I can think of but I'm working on a project and hit a roadblock... I'm experiencing a question with `std::vector` in C++17 where resizing the vector seems to lead to unexpected data loss when using `emplace_back`. I have a class `MyData` that stores some attributes, and I'm attempting to dynamically add objects of this class to a vector. Here's a simplified version of my code: ```cpp #include <iostream> #include <vector> class MyData { public: MyData(int value) : value(value) {} int value; }; int main() { std::vector<MyData> myVec; for (int i = 0; i < 10; ++i) { myVec.emplace_back(i); if (i == 5) { myVec.resize(3); // Intentionally reducing size } } for (const auto &data : myVec) { std::cout << data.value << ' '; } return 0; } ``` When I run this code, I expect to see the values `0 1 2` printed out, but instead, I am seeing `0 1 2` followed by some garbage values or no output at all. It appears that resizing the vector causes some of the newly added elements to be lost or invalidated. I’ve read that `emplace_back` constructs the object in place, and I've ensured that my vector doesn't hold pointers or references to the objects being created. I’ve also tried using `push_back` instead of `emplace_back`, but the behavior remains the same. Is there something I'm overlooking when it comes to the lifecycle of the objects within the vector, especially in relation to resizing? Any insights on how to prevent this data loss would be greatly appreciated! Thanks in advance! Any advice would be much appreciated. This is part of a larger desktop app I'm building. What are your experiences with this? I'm on Windows 11 using the latest version of C++. Thanks for any help you can provide!