Description in VS .NET

Encoder Data Matrix in VS .NET Description

size_type count(const key_type &k) const; Returns the number of times k occurs in the map (1 or zero) bool empty( ) const; iterator end( ); const_iterator end( ) const; pair<iterator, iterator> equal_range(const key_type &k); pair<const_iterator, const_iterator> equal_range(const key_type &k) const; void erase(iterator i); void erase(iterator start, iterator end); size_type erase(const key_type &k); iterator find(const key_type &k); const_iterator find(const key_type &k) const; allocator_type get_allocator( ) const; iterator insert(iterator i, const value_type &val); template <class InIter> void insert(InIter start, InIter end); pair<iterator, bool> insert(const value_type &val); Returns true if the invoking map is empty and false otherwise Returns an iterator to the end of the map Returns a pair of iterators that point to the first and last elements in the map that contain the specified key Removes the element pointed to by i Removes the elements in the range start to end Removes from the map elements that have keys with the value k Returns an iterator to the specified key If the key is not found, then an iterator to the end of the map is returned Returns map s allocator Inserts val at or after the element specified by i An iterator to the element is returned Inserts a range of elements Inserts val into the invoking map An iterator to the element is returned The element is inserted only if it does not already exist If the element was inserted, pair<iterator, true> is returned Otherwise, pair<iterator, false> is returned Returns the function object that compares keys

Table 21-4

iterator lower_bound(const key_type &k); Returns an iterator to the first element in const_iterator the map with the key equal to or greater lower_bound(const key_type &k) const; than k

size_type max_size( ) const; mapped_type & operator[ ] (const key_type &i); reverse_iterator rbegin( ); const_reverse_iterator rbegin( ) const; reverse_iterator rend( ); const_reverse_iterator rend( ) const; size_type size( ) const; void swap(map<Key, T, Comp, Allocator> &ob); The map Member Functions (continued)

Returns the maximum number of elements that the map can hold Returns a reference to the element specified by i If this element does not exist, it is inserted Returns a reverse iterator to the end of the map Returns a reverse iterator to the start of the map Returns the number of elements currently in the map Exchanges the elements stored in the invoking map with those in ob

iterator upper_bound(const key_type &k); Returns an iterator to the first element in const_iterator the map with the key greater than k upper_bound(const key_type &k) const; value_compare value_comp( ) const; Returns the function object that compares values

Table 21-4

You can construct a pair by using either one of pair s constructors, or by using make_pair( ), which constructs a pair object based upon the types of the data used as parameters make_pair( ) is a generic function that has this prototype: template <class Ktype, class Vtype> pair<Ktype, Vtype> make_pair(const Ktype &k, const Vtype &v); As you can see, it returns a pair object consisting of values of the types specified by Ktype and Vtype The advantage of make_pair( ) is that the types of the objects being stored are determined automatically by the compiler, rather than being explicitly specified by you The following program illustrates the basics of using a map It stores 10 key/value pairs The key is a character and the value is an integer The key/value pairs stored are A B C 0 1 2

and so on Once the pairs have been stored, you are prompted for a key (ie, a letter between A and J), and the value associated with that key is displayed

// A simple map demonstration #include <iostream> #include <map> using namespace std; int main() { map<char, int> m; int i; // put pairs into map for(i=0; i<10; i++) { minsert(pair<char, int>('A'+i, i)); } char ch; cout << "Enter key: "; cin >> ch; map<char, int>::iterator p; // find value given key p = mfind(ch); if(p != mend()) cout << p->second; else cout << "Key not in map\n"; return 0; }

Notice the use of the pair template class to construct the key/value pairs The data types specified by pair must match those of the map into which the pairs are being inserted Once the map has been initialized with keys and values, you can search for a value, given its key, by using the find( ) function find( ) returns an iterator to the matching element or to the end of the map if the key is not found When a match is found, the value associated with the key is contained in the second member of pair In the preceding example, key/value pairs were constructed explicitly, using pair<char, int> While there is nothing wrong with this approach, it is often easier to use make_pair( ), which constructs a pair object based upon the types of the data used as parameters For example, assuming the previous program, this line of code will also insert key/value pairs into m:

minsert(make_pair((char)('A'+i), i));

Here, the cast to char is needed to override the automatic conversion to int when i is added to A Otherwise, the type determination is automatic