How to Efficiently Extract Keys and Values from a std::map?

How to Effortlessly Retrieve Keys and Values from std::map

Your approach using functors and standard algorithms is functional and demonstrates flexibility. However, for readability and maintenance purposes, you might consider these alternative solutions.

Vectorizing with Iterators

For retrieving keys into a vector, consider the following:

std::map<int, int> m;
std::vector<int> keys, values;

for (auto& [key, value] : m) {
  keys.push_back(key);
  values.push_back(value);
}

Exploiting Boost Iterators

If you're working with Boost, leverage its powerful iterators for a cleaner approach:

boost::map<int, int> m;
std::vector<int> keys;

for (boost::tie(it, ignore) = boost::begin(m); it != boost::end(m); ++it) {
  keys.push_back(*it);
}

Further Refinements

Your question notes that std::map lacks dedicated member functions for retrieving keys or values. This may be due to performance considerations, as these operations involve potentially complex underlying data structures.

Ultimately, the choice among these approaches depends on your specific context and preferences. Each method has its advantages and readability concerns.

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