How to Remove Elements from a C Standard Map Based on a Condition?

Equivalent of Remove-If for Standard Maps

Question:

In C , how can I remove a range of elements from a map based on a specified condition using the STL algorithm?

Answer:

While remove_if algorithm is not applicable for associative containers like maps, there exists an equivalent approach using iterators. Here's how you can do it:

bool predicate(const std::pair<int, std::string>& x) {
    return x.first > 2;
}

int main() {
    std::map<int, std::string> aMap;

    // Populate the map...

    std::map<int, std::string>::iterator iter = aMap.begin();
    std::map<int, std::string>::iterator endIter = aMap.end();

    for (; iter != endIter;) {
        if (predicate(*iter)) {
            // Here, increment iter after erasing
            iter = aMap.erase(iter);
        } else {
            ++iter;
        }
    }
}

Explanation:

• The code uses a loop to iterate through the map.
• When an element meets the condition, the iterator is incremented after erasing that element using the erase method.
• This prevents skipping over elements that should be erased.
• Updating the iterator after erasing ensures that the loop proceeds correctly, as iterators may become invalid after erasing an element.

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