How do I find elements with custom comparators with std::unordered_map for embedded targets?

In C++, the std::unordered_map allows for efficient storage and retrieval of key-value pairs. However, when you need to use a custom comparator, it requires some special handling. This is particularly important for embedded systems where memory efficiency and performance are crucial. Below is an example that demonstrates how to utilize a custom comparator with std::unordered_map.

#include #include #include // Custom hash function for strings struct CustomHash { std::size_t operator()(const std::string& s) const { return std::hash<:string>()(s); } }; // Custom comparator for strings struct CustomEqual { bool operator()(const std::string& lhs, const std::string& rhs) const { return lhs.size() == rhs.size() && lhs == rhs; } }; int main() { // Create unordered_map with custom hash and equality std::unordered_map<:string int customhash customequal> umap; // Insert elements umap["apple"] = 1; umap["banana"] = 2; // Access elements std::cout << "apple: " << umap["apple"] << std::endl; std::cout << "banana: " << umap["banana"] << std::endl; return 0; }

C++ std::unordered_map custom comparator embedded systems hash functions custom hash key-value pairs

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