Program 3 • Templates and Iterators Solution

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1. Overview

In this assignment, you will implement template code and not use any template classes from the standard library. You will also write your own code to handle files. Refer to the earlier assignment as to how to open and read files.

You may use the following includes, and if you think anything else is needed, post a question to Piazza : <cassert>, <cerrno>, <cstdlib>, <exception>, <fstream>, <ioma-nip>, <iostream>, <stdexcept>, <string>, <typeinfo>.

Specifically, you may not use any classes that take template parameters, such as <iterator>, <list>, <map>, <pair>, <vector>, except for those you write yourself. Do not use shared_ptr, and instead, explicitly manage pointers yourself using new and delete.

2. Program Specification

The program is specified in the format of a Unix man(1) page.


keyvalue — manage a list of key and value pairs


keyvalue [-@ flags] [ filename . . .]


Input is read from each file in turn. Before any processing, each input line is echoed to cout, preceded by its filename and line number within the file. The name of cin is printed as a minus sign ().

Each non-comment line causes some action on the part of the program, as described below. Before processing a command, leading and trailing white space is trimmed off of the key and off of the value. White space interior to the key or value is not trimmed. When a key and value pair is printed, the equiv-alent of the format string used is “%s = %s\n”. Of course, use <iostream>, not <stdio>. The newline character is removed from any input line before pro-cessing. If there is more than one equal sign on the line, the first separates the key from the value, and the rest are part of the value. Input lines are one of the following :


Any input line whose first non-whitespace character is a hash (#) is ignored as a comment. This means that no key can begin with a hash. An empty line or a line consisting of nothing but white space is ignored.


A line consisting of at least one non-whitespace character and no equal sign causes the key and value pair to be printed. If not found, the mes-sage

key: key not found

is printed. Note that the characters in italics are not printed exactly.

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The actual key is printed. This message is printed to cout.

key =

If there is only whitespace after the equal sign, the key and value pair is deleted from the map.

key = value

If the key is found in the map, its value field is replaced by the new value. If not found, the key and value are inserted in increasing lexico-graphic order, sorted by key. The new key and value pair is printed.


All of the key and value pairs in the map are printed in lexicographic order.

  • value

All of the key and value pairs with the given value are printed in lexico-graphic order sorted by key.


The -@ option is followed by a sequence of flags to enable debugging output, which is written to the standard error. The option flags are only meaningful to the programmer.


Each operand is the name of a file to be read. If no filenames are specified, cin is read. If filenames are specified, a filename consisting of a single minus sign () causes cin to be read in sequence at that position. Any file that can not be accessed causes a message in proper format to be printed to cerr.


  • No errors were found.

    • There were some problems accessing files, and error messages were reported to cerr.

  1. Implementation Sequence

In this assignment, you will constuct a program from scratch, using some of the code from previous assignments.

  1. Study the behavior of misc/pkeyvalue.perl, whose behavior your program should emulate. The Perl version does not support the debug option of your program.

  1. Copy Makefile from your previous assignment, and edit it so that it will build and submit your new assignment.

  1. Implement your main program whose name is main.cpp, and handle files in the same way as the sample Perl code. Instead of trying to use a map, just print debug statements showing which of the five kinds of statements are rec-ognized, printing out the key and value portion of the statement.

  1. Instead of <pair> from the standard library, you will use xpair.

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    1. You will be using a linear linked list to implement your data structure. This is

obviously unacceptable in terms of a real data structures problem, since unit operations will run in O(n) time instead of the proper O(log2 n) time for a bal-anced binary search tree. But iteration over a binary search tree is rather complex and will not contribute to your learning about how to implement tem-plates. And balancing a BST is part of CMPS-101, which is not a prerequisite for this course.

    1. Look at xless.h and misc/testxless.cpp, which show how to create and use an xless object to make comparisons. The listmap class assumes this has already been declared.

    1. The files *.tcc are explicit template instantiations. Templates are type-safe macros and the source is needed at the point where they are compiled.

  1. The main function

Replace the code in the main function to do options analysis. Then, for each input line, use regex_search using regular expressions to parse the line into one of the three kinds of lines described above. Use the field captures to extract the key and value fields. See the example matchlines.cpp, which shows how to use regular expressions from the <regex> library.

5. Template class listmap

We now examine the class listmap, which is partially implemented for you. You need not implement functions that are never called.

  1. template <typename Key, typename Value, class Less=xless<Key>> class listmap

defines the template class with three arguments. Key and Value are the ele-ments to be kept in the list. Less is the class used to determine the ordering of the list and defaults to xless<Key>.

  1. typedef Key key_type; typedef Value mapped_type;

typedef xpair<key_type,mapped_type> value_type;

are some standard names given to usual standard library types. Note that the value type is an xpair, not what is normally thought as the value, which here is called the mapped type.

  1. struct link

represents the list itself and is contained in every node. The list is kept as a circular doubly linked list with the list itself being the start and end, as well as the end() result. In a list with n nodes, there are n + 1 links, each node hav-ing a link, and the list itself having a link, but not node values.

  1. struct node

is a private node used to hold a value type along with forward and backword links to form a doubly linked list. It inherits from struct link. The private function anchor() downcasts from a link to a node.

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    1. listmap();

listmap (const listmap&);

listmap& operator= (const listmap&); listmap (listmap&&);

listmap& operator= (listmap&&); ˜listmap();

The usual six members are overriden and explicitly defined.

    1. iterator insert (const value_type&);

Note that insertion takes a pair as a single argument. If the key is already there, the value is replaced, otherwise there is a new entry inserted into the list. An iterator pointing at the inserted item is returned.

    1. iterator find (const key_type&) const;

Searches and returns an iterator. If find fails, it returns the end() iterator.

    1. iterator erase (iterator position);

The item pointed at by the argument iterator is deleted from the list. The returned iterator points at the position immediately following that which was erased.

    1. iterator begin(); iterator end();

The usual iterator generators. We don’t bother here with a constant iterator.

  1. Template class listmap::iterator

Although the iterator is nested inside the list map, it is easier to read when speci-fied separately.

  1. class listmap<Key,Value,Less>::iterator

specifies precisely which class the iterator belongs to.

  1. friend class listmap<Key,Value>;

Only a listmap is permitted to construct a valid iterator.

  1. iterator (listmap* map, node* where);

The iterator keeps track of both the node and the list as a whole, so that end() can return an iterator ‘‘off the end’’,

  1. value_type& operator*();

Returns a reference to some value type (key and value pair) in the list. Selec-tions are then by dot (.).

  1. value_type* operator->();

Returns a pointer to some value type, from which fields can be selected with an arrow (->).

  1. iterator& operator++(); //++itor iterator& operator–(); //–itor

Move backwards and forwards along the list. Moving off the end with ++ and moving from an end iterator to the last element requires special coding.

  1. void erase();

Removes the key and value pair from the list.

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7. What to Submit

Makefile, README, and all necessary C++ header and implementation files. If you are using pair programming, also submit PARTNER.