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copied!<p><strong>Using a char pointer as a key like you are above is almost certainly not what you want to do.</strong></p> <p>STL containers deal with stored values, in the case of <code>std::unordered_map<char *, unsigned int, ...></code>, you are dealing with pointers to c strings, which may not even be around on subsequent insertion/removal checks.</p> <p>Note that your <code>my_unordered_map</code> is a global variable but you are trying to insert local char arrays a, b, and c. What do you expect your comparison function <code>my_equal_to()</code> to <code>strcmp()</code> when the inserted c strings fall out of scope? (You suddenly have keys pointing to random garbage that can be compared to newly inserted future values.)</p> <p>It is important that STL map keys be copyable values that cannot have their meanings changed by external program behavior. <strong>You should almost certainly use <code>std::string</code> or similar for your key values, even if their construction seems wasteful to you at first glance.</strong></p> <p>The following will work exactly as you intend things to work above, and is vastly safer:</p> <pre><code>#include <unordered_map> #include <iostream> #include <string> using namespace std; // STL containers use copy semantics, so don't use pointers for keys!! typedef unordered_map<std::string, unsigned int> my_unordered_map; my_unordered_map location_map; int main() { char a[10] = "ab"; location_map.insert(my_unordered_map::value_type(a, 10)); char b[10] = "abc"; location_map.insert(my_unordered_map::value_type(b, 20)); char c[10] = "abc"; location_map.insert(my_unordered_map::value_type(c, 20)); cout << "map size: " << location_map.size() << endl; my_unordered_map::iterator it; if ((it = location_map.find("abc")) != location_map.end()) { cout << "found \"" << it->first << "\": " << it->second << endl; } return 0; } </code></pre>

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