Map operators

Syntax:

    #include <map>
    mapped_type& operator[]( const key_type& key );
    map& operator=(const map& c2);
    bool operator==(const map& c1, const map& c2);
    bool operator!=(const map& c1, const map& c2);
    bool operator<(const map& c1, const map& c2);
    bool operator>(const map& c1, const map& c2);
    bool operator<=(const map& c1, const map& c2);
    bool operator>=(const map& c1, const map& c2);

Maps can be compared and assigned with the standard comparison operators: ==, !=, <=, >=, <, >, and =. Individual elements of a map can be examined with the [] operator.

Performing a comparison or assigning one map to another takes linear time.

Two maps are equal if:

  1. Their size is the same, and
  2. Each member in location i in one map is equal to the the member in location i in the other map.

Comparisons among maps are done lexicographically.

For example, the following code defines a map between strings and integers and loads values into the map using the [] operator:

    struct strCmp {
      bool operator()( const char* s1, const char* s2 ) const {
        return strcmp( s1, s2 ) < 0;
      }
    };
 
    map<const char*, int, strCmp> ages;
    ages["Homer"] = 38;
    ages["Marge"] = 37;
    ages["Lisa"] = 8;
    ages["Maggie"] = 1;
    ages["Bart"] = 11;
 
    cout << "Bart is " << ages["Bart"] << " years old" << endl;
 
    cout << "In alphabetical order: " << endl;
    for( map<const char*, int, strCmp>::iterator iter = ages.begin(); iter != ages.end(); ++iter ) {
      cout << (*iter).first << " is " << (*iter).second << " years old" << endl;
    }

When run, the above code displays this output:

    Bart is 11 years old
    In alphabetical order:
    Bart is 11 years old
    Homer is 38 years old
    Lisa is 8 years old
    Maggie is 1 years old
    Marge is 37 years old

Related Topics: insert, Map Constructors & Destructors