👀 Views: 4 💬 Answers: 1 📅 Created: 2025-06-02

cpp20 stdfunction lambda cpp

I'm following best practices but I've been banging my head against this for hours... I've looked through the documentation and I'm still confused about I'm encountering unexpected behavior when trying to store a lambda function in a `std::function` that captures local variables. My project is using C++20, and I've modified my code to utilize lambdas with captures for callback handling. Here's a simplified version of my problem: ```cpp #include <iostream> #include <functional> #include <vector> void executeCallbacks(const std::vector<std::function<void()>>& callbacks) { for (const auto& callback : callbacks) { callback(); } } int main() { int counter = 0; std::vector<std::function<void()>> callbacks; // Lambda capturing counter callbacks.emplace_back([&counter]() { std::cout << "Counter: " << counter << std::endl; }); counter = 5; executeCallbacks(callbacks); return 0; } ``` The output I expect is `Counter: 5`, but instead, I'm getting `Counter: 0`. It seems that the lambda is not capturing the updated value of `counter` properly. I've double-checked that `counter` is modified before calling `executeCallbacks`, and I also ensured that I'm passing the correct lambda to the vector. I thought that the capture by reference should work as intended, but it looks like the lambda is retaining the value of `counter` at the time of capture. I've tried changing the capture to by value and passing `counter` directly, but then I’m getting the stale value (which is also not what I want). I'm not sure if this is expected behavior or a misunderstanding of how lambdas with captures work in C++20. Any insights would be greatly appreciated! I'm working on a web app that needs to handle this. Thanks in advance! I'm working on a service that needs to handle this. What's the best practice here? Any suggestions would be helpful. This is happening in both development and production on Linux. I'm open to any suggestions.