CrossPlatform GUI Programming with wxWidgets [Electronic resources] نسخه متنی

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;
}