关于

maxon::HashMap is a generic class template for a map that maps keys to values with the help of hash values. It can use data types as a key that implement a "GetHashCode" and "IsEqual" function. maxon::HashMap is based on maxon::MapBase and maxon::Collection .

创建

A new hash map object can simply be created using the class template:

// This example creates a hash map and inserts two elements. // The hash map stores maxon::String values using maxon::Int keys.

maxon::HashMap<maxon::Int, maxon::String> atoms;

atoms. Insert (1, "Hydrogen" _s) iferr_return ; atoms. Insert (2, "Helium" _s) iferr_return ;

The data stored in a maxon::HashMap can be cleared with:

maxon::HashMap::Reset() : Destructs all entries and frees any memory held by the map.
maxon::HashMap::Flush() : Destructs and frees all entries, but does not free the bucket table.

Access

An entry in a maxon::HashMap is represented as a maxon::HashMap::Entry object. New entries can be inserted with:

maxon::HashMap::Insert() : Inserts the given value using the given key.
maxon::HashMap::InsertEntry() : Inserts a maxon::HashMap::Entry for the given key.
maxon::HashMap::InsertKey() : Inserts an entry for the given key and returns a pointer to the stored value.
maxon::HashMap::InsertCtor() : Inserts an entry for the given key and creates a new value using the given constructor.
maxon::HashMap::InsertLambda() : Inserts an entry for the given key using the given lambda function.
maxon::HashMap::InsertMultiEntry() : Inserts an entry for the given key. If an entry already exists the hash map is turned in to a multi-map.

// This example creates a hash map and inserts elements in various ways. maxon::HashMap<maxon::Int, maxon::String> atoms;

// insert data atoms. Insert (1, "Hydrogen" _s) iferr_return ;

// insert data maxon::Bool created = false ; auto e = &atoms. InsertEntry (2, created) iferr_return ; if (created && e) e->SetValue( "Helium" _s);

// insert data maxon::String & str = atoms. InsertKey (3, created) iferr_return ; str = "Lithium" _s;

// insert data auto lambda = []( maxon::HashMap<maxon::Int, maxon::String>::Entry & entry) -> maxon::Result<void> { entry.SetValue( "Beryllium" _s); return maxon::OK ; }; atoms. InsertLambda (4, lambda) iferr_return ;

// insert data (multi-map) e = &atoms. InsertMultiEntry (1) iferr_return ; if (e) e->SetValue( "Deuterium" _s);

An entry stored in the maxon::HashMap can be found using the proper key:

maxon::HashMap::Find() : Returns the entry for the given key.
maxon::HashMap::FindValue() : Returns the value stored for the given key.

// This example gets the values for a given keys in the hash map.

// find key "1" auto e = atoms. Find (1); if (e) DiagnosticOutput (e->GetValue());

// find key "2" const maxon::String * const str = atoms. FindValue (2); if (str) DiagnosticOutput (*str);

An entry of the maxon::HashMap can also be deleted:

maxon::HashMap::Erase() : Removes the given entry.
maxon::HashMap::DeleteEntry() : Deletes an entry which has been removed previously. Only needed if Erase() was used with specific parameters.

// This example searches the entry for the given key and deletes it.

// find entry for key "1" maxon::HashMap<maxon::Int, maxon::String>::Entry * e = nullptr ; e = atoms. Find (1); if (e) { atoms. Erase (e, true ) iferr_return ; }

It is easily possible to iterate trough all stored key and values with:

maxon::HashMap::GetKeys() : Returns an iterator for all keys.
maxon::HashMap::GetValues() : Returns an iterator for all stored values.
maxon::HashMap::FindAll() : Returns an iterator for all values stored for a given key. See maxon::MultiEntryIterator<T>.

另请参阅 Iterate .

// This example loops through all keys and value of the given hash map // and the multi-map values of a given key.

// list all keys for ( const maxon::Int & key : atoms. GetKeys ()) DiagnosticOutput ( "Key: @" , key);

// list all values for ( const maxon::String & value : atoms. GetValues ()) DiagnosticOutput ( "Values: @" , value);

// list multi-map values of given key for ( const auto & it : atoms. FindAll (1)) { const auto value = it.GetValue(); DiagnosticOutput ( "Value: @" , value); }

A maxon::HashMap stores a certain number of elements and has a certain capacity to store further elements:

maxon::HashMap::GetCount() : Returns the number of stored entries.
maxon::HashMap::SetCapacityHint() : Ensures that the bucket table is large enough to hold at least the given number of entries.
maxon::HashMap::ResizeTable() : Resizes the bucket table.
maxon::HashMap::GetTableSize() : Returns the size of the bucket table.
maxon::HashMap::GetMemorySize() : Returns the memory usage of the map if the key and value implement GetMemorySize() .
maxon::HashMap::GetNonEmptyBucketCount() : Returns the number of non-empty buckets.
maxon::HashMap::GetNonEmptyBucket() : Returns the non-empty bucket of the given index.

// This example reads data from the given hash map. const maxon::Int count = atoms. GetCount (); const maxon::Int nonEmptyCount = atoms. GetNonEmptyBucketCount (); const maxon::Int tableSize = atoms. GetTableSize ();

Iterate

It is easily to iterate over all entries in the maxon::HashMap :

maxon::HashMap::Begin() : Returns the iterator pointing at the start of the list.
maxon::HashMap::End() : Returns the iterator pointing at the end of the list.
maxon::HashMap::GetIterator() : Returns the iterator for the given entry.

// This example loops through all entries of the given hash map.

// loop through all key/value pairs for ( const auto & e : atoms) { const maxon::Int & key = e. GetKey (); const maxon::String & value = e. GetValue (); DiagnosticOutput ( "Key: @, Value: @" , key, value); } auto e = atoms.Find(1); if (e) { auto it = atoms.GetIterator(e);

// next element ++it; const maxon::Int & key = it. GetKey (); const maxon::String & value = it.GetValue(); DiagnosticOutput ( "Key: @, Value: @" , key, value); }