How can I customize the comparator for a map in C to sort keys by their length?

Customizing Comparators for Maps

In C , std::map uses a comparator to order its elements. By default, maps use the less-than operator (<) to compare keys. However, it is possible to override this default behavior by providing a custom comparator.

This question discusses how to customize the comparator for a map to sort keys by their length rather than alphabetically. Here's the solution:

Solution using a Custom Class

std::map allows for up to four template type arguments, the third one being a comparator. Here's an example of a custom class that implements a comparator based on string length:

<code class="cpp">struct cmpByStringLength {
    bool operator()(const std::string& a, const std::string& b) const {
        return a.length() < b.length();
    }
};

To use this custom comparator, create a map with the following template arguments:

<code class="cpp">std::map<std::string, std::string, cmpByStringLength> myMap;</p>
<p><strong>Solution using Constructor Argument</strong></p>
<p>Alternatively, you can pass a comparator to the map's constructor. This syntax is equivalent to the previous example:</p>
<pre class="brush:php;toolbar:false"><code class="cpp">std::map<std::string, std::string, cmpByStringLength> myMap(cmpByStringLength());</code>

Note: When comparing by length, only one string of each length can be present in the map as a key.

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