How do I avoid rehashing overhead with std::unordered_map for embedded targets?

Using std::unordered_map in C++ can sometimes lead to performance overhead due to rehashing, especially on embedded targets where resources are limited. To avoid this overhead, you can reserve the space necessary for your expected number of elements ahead of time. This approach minimizes the need for dynamic resizing and rehashing.

Here’s an example approach:

#include #include int main() { // Create an unordered_map and reserve space for 100 elements std::unordered_map myMap; myMap.reserve(100); // Insert elements for (int i = 0; i < 100; ++i) { myMap[i] = "Value " + std::to_string(i); } // Access elements for (const auto& pair : myMap) { std::cout << pair.first << ": " << pair.second << std::endl; } return 0; }

std::unordered_map rehashing performance overhead embedded targets C++ performance

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