Map operators

  #include <map>
  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