maps.cpp

斯坦福Energy211/CME211课《c++编程——地球科学科学家和工程师》的课件

// Program that demonstrates maps and multimaps

#include <iostream>
#include <fstream>
#include <map>

using namespace std;

// Use typedef to shorten type names

// Map with string keys and string values
typedef map<string, string> namemap;
// Iterator for namemap
typedef map<string, string>::iterator name_iter;

// Multimap with string keys and string values
typedef multimap<string, string> coursemap;
// Iterator for coursemap
typedef multimap<string, string>::iterator course_iter;

int main() {
	
	// File names.txt contains first and last names
	// of students, and which course they are enrolled in
	// (energy211 or cme211)
	ifstream namefile("names.txt");
	// map of last name to first name
	namemap names;
	// multimap of course to last names
	coursemap courses;
	// Keep reading from the file until no more are left
	while ( !namefile.eof() )
	{
		string first_name;
		string last_name;
		string course;
		// Read one student's info
		namefile >> first_name;
		namefile >> last_name;
		namefile >> course;
		// Add entry (last_name,first_name) to names map
		names[last_name] = first_name;
		// Add entry (course,last_name) to courses multimap
		courses.insert( make_pair( course, last_name ) );
	}
	
	// Print out all entries in names map
	// Use begin() iterator to initialize iterator i that
	// iterates over all elements
	for ( name_iter i(names.begin()); i != names.end(); i++ )
	{
		// Iterator points to a pair object consisting of
		// the name and the value.  Syntax i->first is 
		// equivalent to (*i).first.  -> operator accesses
		// members from pointers to objects.  A pair object
		// has members first and second.  In this case,
		// first is the key and second is the value
		cout << i->first << ", " << i->second << endl;
	}

	// This looks up a last name in the names map and returns
	// the corresponding value (first name), if found
	cout << "Enter a last name: ";
	string last;
	cin >> last;
	// Use [] operator to retrieve value from key
	string first = names[last];
	// If [] doesn't find a value, it returns a default
	// value, which is the empty string "" in this case
	if ( first.size() > 0 )
		cout << "First name is " << first << endl;
	else
		cout << "Name not found" << endl;
	
	// This looks up a course in the course multimap and
	// prints all of the corresponding values
	cout << "Enter a course: ";
	string course;
	cin >> course;
	cout << "Students enrolled in " << course << ":" << endl;
	// Instead of using [], since there can be more than
	// one value, we use the functions lower_bound() and
	// upper_bound() to iterate over all of the values.
	// lower_bound() plays a similar role to begin() for
	// iterating over all elements, and upper_bound() plays
	// a similar role to end()
	course_iter begin( courses.lower_bound( course ) );
	course_iter end( courses.upper_bound( course ) );
	// Once again, the iterator points to a pair
	for ( ; begin != end; begin++ )
		cout << begin->second << ", " << 
			names[begin->second] << endl;

	return 0;
}