wxHashMap

The wxHashMap class is a simple, type-safe, and reasonably efficient hash map class, with an interface that is a subset of the interface of STL containers. In particular, the interface is modeled after std::map and the non-standard std::hash_map. By using macros to create hash maps, you can choose from several combinations of keys and values, including int, wxString, or void* (arbitrary class).

There are three macros for declaring a hash map. To declare a hash map class named CLASSNAME with wxString keys and VALUE_T values:

 WX_DECLARE_STRING_HASH_MAP(VALUE_T, CLASSNAME); 

To declare a hash map class named CLASSNAME with void* keys and VALUE_T values:

 WX_DECLARE_VOIDPTR_HASH_MAP(VALUE_T, CLASSNAME); 

To declare a hash map class named CLASSNAME with arbitrary keys or values:

 WX_DECLARE_HASH_MAP(KEY_T, VALUE_T, HASH_T, KEY_EQ_T, CLASSNAME); 

HASH_T and KEY_EQ_T are the types used for the hashing function and key comparison. wxWidgets provides three predefined hashing functions: wxInteger Hash for integer types (int, long, short, and their unsigned counterparts), wxStringHash for strings (wxString, wxChar*, char*), and wxPointerHash for any kind of pointer. Similarly, three equality predicates are provided: wxInteger Equal, wxStringEqual, and wxPointerEqual.

The following code example shows the wxHashMap methods as well as how to create and use your custom hash type.

 // Our data class to store in the hash class Customer {     public:         int CustID;         wxString CustName; }; // Declare our hash map class // This macro declares and implements CustomerList as a hash map WX_DECLARE_HASH_MAP(int, Customer*, wxIntegerHash,                     wxIntegerEqual, CustomerHash); void HashTest() {     // Declare an instance of our list     CustomerHash MyHash;     bool IsEmpty = MyHash.empty(); // will be true     // Create some customers     Customer* CustA = new Customer;     CustA->CustID = 10;     CustA->CustName = wxT("Bob");     Customer* CustB = new Customer;     CustB->CustID = 20;     CustB->CustName = wxT("Sally");     Customer* CustC = new Customer;     CustC->CustID = 5;     CustC->CustName = wxT("Dmitri");     // Add the customers to the hash     MyHash[CustA->CustID] = CustA;     MyHash[CustB->CustID] = CustB;     MyHash[CustC->CustID] = CustC;     int Size = MyHash.size(); // will be 3     // count returns 0 or 1, i.e. is 20 in the hash?     int Present = MyHash.count(20); // will be 1     // Customized iterator for our hash map     CustomerHash::iterator i = MyHash.begin();     // End represents one past the last element     while (i != MyHash.end())     {         // first is the key, second is the value         int CustID = i->first;         Customer* Cust = i->second;         // Process Customer         // Advance to the next element in the hash         i++;     }     // Remove Customer A from the hash     MyHash.erase(10);     // CustA object is NOT deleted by removing from hash     delete CustA;     // Return an iterator to the node with the specified key     CustomerHash::iterator i2 = MyHash.find(21);     // Find returns hash::end if the key was not found     bool NotFound = (i2 == MyHash.end()); // will be true     // This time the find will be successful     i2 = MyHash.find(20);     // Removing an element using the iterator     MyHash.erase(i2);     delete CustB;     // Side-effect: A NULL value is inserted in the hash for key 30     Customer* Cust = MyHash[30]; // Cust will be NULL     // Empties the hash map of all elements     MyHash.clear();     delete CustC; }