Issue with using std::vector and std::vector::reserve() causing performance degradation in C++17
I need help solving I'm experiencing significant performance degradation when using `std::vector` with `reserve()` in C++17. I have a scenario where I need to read a large number of elements from a file and store them in a vector for processing later. Initially, I used `std::vector<int> myVector;` and kept pushing back elements without reserving any space. However, I noticed that the performance was quite slow, especially with large datasets (over 1 million integers). To improve this, I switched to using `myVector.reserve(expected_count);` before populating it. My expectation was that reserving would help avoid reallocations, but instead, it seems to cause even slower performance than pushing back without reserving. Here's a simplified version of my code: ```cpp #include <iostream> #include <vector> #include <fstream> int main() { std::vector<int> myVector; size_t expected_count = 1000000; myVector.reserve(expected_count); std::ifstream file("data.txt"); int number; while (file >> number) { myVector.push_back(number); } // Process myVector return 0; } ``` I noticed that when I do not call `reserve()`, the initial performance is indeed worse, but the overall time to complete is faster compared to reserving. Additionally, my profiling tools show that the time spent in `push_back()` is higher when `reserve()` is used. I'm unsure if I'm missing something or if there's a caveat I should be aware of regarding `reserve()` in certain contexts. Has anyone else faced something similar? Are there better practices for using `std::vector` when high performance is a requirement? I'm working with C++ in a Docker container on CentOS. Any advice would be much appreciated.