25.4 Storing Grades in a STL Map

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Let's change our class roster so that we record not only the name of each student, but also the student's grade as well. We do this using something called a map . To define our class map, we use the following declaration:

 #include <map> // Map key=name(string), value = grade(char) template map<string, char> student_roster; 

Inserting an item into a map is a little trickier that inserting one into a set because we are inserting a pair of items. The STL handles this nicely by providing a pair class that takes two elements and turns them into an item that a map can handle. For example, if John Smith is in the class and got an A, we would write:

 student_roster(pair(string("John Smith"), 'A')); 

Suppose we want to find out what Mr. Smith's grade is. We can search for his record using the find function call. It takes three parameters: a place to start the search, a place to end the search, and something to look for. It returns an iterator pointing to the item found or, if nothing is found, the value returned by the end function. To look for Mr. Smith's grade, we use the code:

 map<string, char>::const_iterator record_loc;     record_loc = find(student_roster.begin(), student_roster.end(  );                     string("John Smith")); 

Now let's check to see if we found the student:

 if (record_loc == student_roster.end(  ))         std::cerr << "John Smith not found in the class\n"; 

The iterator points to a pair consisting of the student's name and grade. The fields of a pair are named first and second . To print John's record, we use the statement:

 std::cout << "Student: " << record_loc->first << " Grade:" <<          record_loc->second << '\n'; 

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