C++ STL FAQ
   This FAQ deals with the containers, iterators,
and algorithms sections of the C++ Standard,
Clauses 23, 24 and 25.

If you have any questions you had while working with the
STL and answers you received or worked out, please
submit them to me for inclusion. I will give you credit
for it if you include your name.

Thanks,
Marian Corcoran
mcorcora@ix.netcom.com
Copyright (c) 1995, Marian Corcoran
This may be freely distributed, but not sold.
No guarantees.

update 1/16/96

Article:
1.  Glass, Graham. "Extending STL." C++ Report, Jan, 1996.

2.  New e-mail list for STL discussion started
  To post to the list, send email to

  genstl@atext.com

To ask to be added or removed from the list, send email to

  genstl-request@atext.com

with the word "subscribe" or "unsubscribe" in the Subject line.

This mailing list is devoted to STL (the C++ Standard Template Library)
and the style of generic programming it exemplifies.  Appropriate
topics
for discussion include the following:

- The effective use of STL.
- The design of STL.
- Possible extensions to STL.
- STL programming questions.
- Language-related issues, e.g., language extensions to C++ or other
languages
  that would make generic programming easier.
- Traps and pitfalls in using STL.
- Design principles, strategies, and techniques for producing libraries
of
  generic software components.
- Specifying and reasoning about generic algorithms (e.g.,
  required properties of iterators).
- Application areas to target for the development of their own
libraries
  of generic software components.
- Announcements of papers and other publications.

The following are NOT appropriate for this list:

- Flames
- Questions that can be answered by reading Marian Corcoran's STL FAQ,
  which is posted regularly to comp.lang.c++ and can also be obtained
  at ftp://butler.hpl.hp.com/stl/stl.faq.

3.  Whitepaper on using STL with VC++ 4
  http://www.microsoft.com/devonly/visualc

update 12/1/95

1. New Books and Articles:
   Glass, Graham.  STL Primer.  Prentice-Hall, 1995.
     Based on ObjectSpace Manual.
   Musser, David.  STL Tutor and Reference.  Addison-Wesley, 1995.
   Nelson, Mark.  C++ Programmer Guide to STandard Template
      Library Programming. IDG Books, 1995.
     Good introduction.
   Plauger, P.J.  Has an article on STL in C/C++ Users
      Journal, Dec 1995.
2. Added questions 6 and onward in Q & A part.

3. RogueWave STL to be included in Borland C++ Compiler.

4. The following comes from one of my students in my STL course:
   After managing to install the ObjectSpace STL<Toolkit> with the
   Watcom
   C++/C 10.5 compiler, I wrote notes on the subject in FAQ format.
   The experience was positive - the two work well together.
   I humbly hope that this may be of others who need to install this
   version of the STL under a compiler which is not Borland, MS, or
gnu,
   or on a platform other than DOS/Win or unix (I used Warp).
   I placed the ASCII text version of the faq in:
   ftp.netcom.com/pub/me/medina/C++/objectspace_and_watcom_faq.txt
   (with a web browser, place the string, "ftp://" ahead of that
address.)
   -- Sean Medina
update 9/2/75
   Two excellent articles have appeared on the STL

Dawes, Beman.  "You Can Count On It."  C/C++ Users
    Journal, July, 1995.  Excellent intro material.
Zigmond, Dan. "Generic Programming and the C++ STL."
    Dr. Dobb's Journal, August, 1995.  Another good
    sample program.

Rogue-Wave will be providing the STL to the following
vendors: HP, SGI, SunSoft, Siemens-Nixdorf

update 7/3/95
   Started adding new sections on questions

Of special note:  A major complaint about libraries that
programmers have is that you don't get the source.  Well,
with STL, you get the source.  STL source is
also excellent code to study.  It is very well written code.

CONTENTS

I have put together four articles for the STL FAQ:
  I.    Sources
  II.   Questions
  III.  References of STL (M. Corcoran).
  IV.   Report from Lockheed on their first experiences
        with STL.
  V.    On using MODENA by Edgar Crisostomo (along with some
  needs in education that he sees for STL)
  VI.   Comparison of Modena and ObjectSpace by Mike Lindner.

REQUEST FOR OTHER MATERIAL  If someone has other material
or experiences to include you may e-mail them to me and
I will add them.  Especially of interest would be
examples of STL that you may have developed as you
learn STL or industrial applications or porting
instructions for different platforms.  Please state
whether I may use your article in the FAQ and whether
I may use your name.

Marian
===============================================================
PART I  SOURCES

1.  Where does one get the STL?

    A. anonymous ftp via butler.hpl.hp.com
  works with Borland 4.5 and IBM
  also includes something on hash tables
  not in STL by Bob Fraley bfhash.zip
            and David Musser dmhash.zip
     no support included
  to use the public domain version
            of STL with BC4.5
  Projects|Defines  and type __MINMAX_DEFINED
  or use #define __MINMAX_DEFINED before
  #include <iostream.h>

    B. STL++: Modena Software at 1-800-MODENA-1
  works with Borland, IBM C Set++, Apogee,
            Visual C++ 2.0 (this last has some limitations.)
  comes with tutorial, you can get the tutorial

            separately (read this tutorial after A. Stevens
            and after playing with ObjectSpace examples.)

    C. STL<ToolKit>:ObjectSpace at 1-800-OBJECT-1
  most C++ compilers
  code is well documented
       comes with tutorial with over 200 elementary
   examples that have just been placed in the
      public domain available
      via anonymous ftp via butler.hpl.hp.com at
    /STL/examples.Z or .zip for PC
  These examples are a good place to start.


     D. libstdc++ (part of libg++): Free Software Foundation
  anonymous ftp via prep.ai.mit.edu and many other
  machines only some containers exist, but works with GNU
C++,
      and probably many other C++ compilers

     E.  RogueWave to include STL, coming out in first quarter, 1996

===============================================================
PART II  QUESTIONS

1.  What are the iterators, containers, and algorithms
sections of the  STL (Standard Library)?
A.  The STL has a is a data structures or container class
library that has been adopted into the language.  It
consists of three major components:
 Containers or data structures
        Iterators
 Algorithms

2.  What are containers?
Containers include such things as vectors, lists, queues,
priority queues, stacks, maps, and sets.  In STL,
containers (data structures) are templatized.  For
example, the stack class may be used with integers,
doubles, and user defined types.

3.  What are iterators?
Iterators may be thought of as the key to STL, acting
as an intermediary between the algorithms and the
containers.  You are already familiar with the concept
of an iterator when you think of the pointer used to
traverse an array.  Iterators are objects in STL.
One may think of them as a finger moving across the
elements of a container.  The five categories of
iterators are:

   Random Access -> Bidirectional-> Forward -> Input
                -> Output
4.  How are iterators related to containers and
algorithms?
One may think of each container and each algorithm as
being associated with a certain iterator.  A vector has
a random access iterator, therefore it may use a random
access algorithms such as a sort.  A container may use
any algorithm associated with its iterator or any
algorithm associated with an iterator to the right of
it in the above diagram. Therefore a vector (random
access iterator) may use algorithms associated with
bidirectional, forward, input or output iterators.
Can a vector be used with the binary_search algorithm
(takes a forward iterator) ?  If we look at the diagram
above, forward is to the right of random access,
therefore we may use binary_search with a vector
container.  Can a vector be used with copy (takes an
input and an output iterator)?  Since input and output
are to the right of random access, vector may used
with copy.

There are quite a number of algorithms in STL,
including count(), copy(), replace( ), reverse( ), ...
Just as each container is associated with a certain
iterator, each algorithm is also associated with a
certain iterator(s).

count( ) - input iterator
copy ( ) - input and output iterator
replace( ) - forward iterator
reverse( ) - bidirectional iterator

6.  I got the ObjectSpace examples and they don't work
with the HP STL.  I get an error message that there
is no Stl.h file.

A.  ObjectSpace compiled all the different files of the
STL together.  This is helpful when first learning
it.  However, later you will probably want to include
just the files you need.
     A rule of thumb here is to always include the algo.h
or algorith.h (latter for ObjectSpace) file and then
nclude the file with the container you are using:

list - list.h
stack, queue, priority_queue - stack.h
deque - deque.h
vector - vector.h
map - map.h
multimap - multimap.h
set - set.h
multiset - multiset.h

7.  When I try to use HP STL with Borland 4.5,
I get an error function min and max already
defined.  Why?

The functions min( ) and max( ) are already defined
in the stdlib.h file.  However, there is #ifdef to
compile them only if they are already not defined.
Therefore, you may place a __MINMAX_DEFINED  line in
your Project|Defines window of put the line
#define __MINMAX_DEFINE before the
#include <iostream.h>

8.  Where is the code for the STL?  When I downloaded
STL from the HP site, I only got header files.

The code for the STL is in the .h files

9.  I hear the STL is extensible.  What does that mean?
How will different vendors extend the STL?

Extensible means that one will be able to add algorithms,
containers, and iterators to the STL.
Joe Buck (jbuck@synopsis.com) writes:
Rogue Wave is now giving a January 1996 date for STL
inclusion.  See

http://www.roguewave.com/rwpav/products/stdlibwp.htm

for discussion of their plans for including STL support
in their Tools.h++ class library.

Reading that paper, and looking at what ObjectSpace has
done (see http://www.objectspace.com/products/stl/), it
seems that vendors are making their own enhancements to
the libraries, generally in the same direction: to make
the library somewhat less low-level, to provide cleaner
interfaces for the very common

 algorithm(container.begin(), container.end())

so that one can write something like algorithm(container)
(in ObjectSpace's case) or container.algorithm() (in
Rogue Wave's case).

Perhaps the committee should consider doing a little bit in
this area, before every library vendor does it differently?
It seems that there are fairly natural interfaces that could
be provided to cover the common cases where a range that
is the entire container is to be specified, where the user
is thinking "sort the container" or "copy container A to
container B".  If the committee doesn't provide them, they
will still be there, based on what vendors are already
doing, but they will be non-portable.




==============================================================
PART III  REFERENCES

A. PERIODICALS
    D. Jordan. ODMG Update: Collections in ODMG-93
    Discusses ODMG and STD LIB.  C++ Report, June 1995
    A. Koenig. File iterators. Journal of Object-oriented
  Programming  (JOOPS), Nov/Dec 1994
    A. Koenig. Generic iterators. JOOPS, Sept. 1994
    A. Koenig. Templates and generic iterators.
 JOOPS, June 1994
    A. Koenig. ? . January , 1995
    D.R. Musser and A.A. Stepanov. Algorithm-oriented
       generic libraries.  Software-Practice and Experience,
       July 1994
    N. Meyers. A New and Useful Template Technique:
       "Traits" C++ Report, June 1995
    A.A. Stepanov and M.Lee.  The Standard Template
      Library. ISO Programming Language C++ Project.
      Doc. No. X3J16/94-0095, WG21/N0482, May 1994.
      (Look in HP's ftp for stl.doc, I believe).
       Although it is the
 "definitive" STL, it is not intro material.
    A. Stevens. He has an interview with Stepanov in
      Dr. Dobb's Journal, March 1995.  This is an
      excellent conceptual introduction to the STL,
      also a good place to start.
    A. Stevens.  The Standard Template Library
       (with some code) in his column, Dr. Dobb's Journal,
       April 1995.  Also good intro material.
    B. Stroustrup. Making a vector fit for a standard.
        C++ Report, Oct. 1994. intermediate level
        material. Stroustrup made some important
        contributions to the design of STL, discussed
        here.
    M.J. Vilot. An introduction to the standard template
  library.  C++ Report, Oct 1994. You might want to read
 Stevens and Dawes first.
    Also see
 http://www.cs.rpi.edu/~musser/STL.html
 This material is also available via anonymous ftp
       ftp.cs.rpi.edu in directory pub/STL the file
 STL-info.ps.Z
  includes STD LIB Online Algorithm Reference
      by R. Cook,
 D. Musser, and K Zalewski with examples.
 See ObjectSpace examples first.

  B.  STL Web Pages - "Newbie" guide
 http://weber.u.washington.edu/~bytewave/STL.html
   1.  Intro material including Stepanov Speaks on
       STD LIB in C++  (M. Corcoran),
   2.  Dr. Dobbs article (A. Stevens), STD LIB newbie
       notes (M. Khan),
   3. STD LIB by Stepanov & Lee, STD LIB files, and
      ANSI C++ Draft (HTML version)


==============================================================
PART IV. EXPERIENCES FROM LOCKHEED

We've just obtained STL<ToolKit> for use with our HP
cfront compiler and the Softbench development
environment. Here are the first impressions & observations:

Apparently ObjectSpace doesn't routinely deliver 4mm DAT
tapes and added $25 to do it. The tape we recieved was
DOA (unreadable) but the ObjectSpace support folks quickly
e-mailed the TAR-file and we were in bussiness. We did
not experience the problems reported by Mike Linder
contacting the ObjectSpace people. The above problem w
as solved within two hours.

Our experience with installing and building the
libraries supports Mike Linder's observations.
Good job here by the vendor.

Compiling with the debug option (-g) resulted in many
warnings similar **to the following:

CC: "release1.C", line 28: warning:
debug.emit_type_entry:typedef node has no
symid_ptr: vector <X*> ::size_type (187)
CC: "release1.C", line 28: warning:
debug.emit_type_entry:typedef node
**has no symid_ptr: vector <X*> ::const_reference (187)

The executable does run and the debugger still works,
however.

Note that the person evaluating STL<ToolKit> is
not an experienced C++ programmer and is proceding
on the strength of a C++ class. His first impressions
of the ObjectSpace documentation are favorable and
he was able to write a simple program from a
standing-start in a few hours. We also have the
documentation from HPs public-domain STD LIB.
I'll keep you posted.

===============================================================
PART V. ON USING MODENA at SIEMENS-ROLM

   We use Modena STL++ v2.0 - they respond fairly
quickly to our needs, they add bug fixes or compiler
support for our Unixware 2.0 SDK C++ compiler, and
they answer our many technical questions.

The STD LIB++ Manual has a "Files" Heading at the top
of each component description, and that is all that
should be explicitly #included to use that component
(mutual independence).

When I #include <vector.h>, it pulls in all the other
dependent includes.  It is not explicitly stated, but
for C-like arrays, you #include <algobase.h>.

There are minor problems, I will report to Modena
(example: hashfun.h has non-template function
_definitions_, so you get multiply defined, when
used over several translation units.   To improve
the ability (for us) to specify manual template
instantiation, it would be nice if they factor out
the non-inline template definitions into another file.

EDUCATIONAL HINTS
A discussion of build issues would be useful.  Especially
since STL template code can have really obscure
compiler messages with todays compiler technology.
There are also issues with debugging template code.

A discussion of when to pass container by reference,
versus passing iterators would be useful.

Edgar Crisostomo    408-492-6528,
edgar@clipper.robadome.com
Systems Software,
Siemens Rolm Communications, Inc. FAX 408-492-3305

=============================================================
PART VI
COMPARISON OF MODENA AND OBJECTSPACE

I just bought STL++ from Modena and
STL<toolkit> from ObjectSpace, for purposes of
comparison.  So far I have not had a chance to use
either extensively, but I have the following observations:

Modena was very helpful on the phone, and responded
quickly to whatever I called about.  The initial
floppy they sent me was bad, and they replaced it
overnight.  In every case but one technical question,
the person who answered the phone was able to do
everything I needed.  In the remaining case, I
received a call back within hours of my question.
I like their service.

 ObjectSpace had an operator, who directed me to the
one salesperson, who was always "out of the office"
when I called, and who was the only one who could
sell me the product (it took 5 days just to order
the product, because I couldn't get in touch with her).

Both products come as source, and you must build the
libraries yourself.  The documentation for doing this
from Modena was sketchy, and it wasn't until I called
tech support that I discovered I had to change some
files by hand to make them compile with my compiler
(which is one of the one's they advertise as working with).

ObjectSpace, on the other hand, has a neat little
config package that tests what your compiler can do,
and writes a header file which configures the code
to be correct for your compiler (lots of preprocessor
magic in them there header files).  It was a joy to use.

So far, the test programs I have compiled are much
smaller when I use the ObjectSpace libraries than
with the Modena libraries.  As I said, I have not
stressed either product, so these numbers may not
reflect use in an actual application.

As for conformance, ObjecSpace doesn't necessarily support
everything in STL, but only as much as they can
squeeze out of the compiler you give them to work
with.  Is that good or bad?

The ObjectSpace library claims to be "thread safe",
although I haven't tried that our yet.  Apparently
they have a wrapper class that behaves like a smart
pointer, but can be locked for reading or writing.
They also have some other platform independent thread
and mutex code.

  The Modena folks said their library is not
"thread safe", but only in one place, and they would
gladly show me how to modify the source to add that
feature.  One of my compiler vendors says they'll be
shipping Modena with their compiler soon, and their
version will be thread safe.

Modena includes some extra goodies, like hash tables
and an ANSI string class.
ObjectSpace has added some features recently as well.

Mike Lindner
mikel@attmail.com
mpl@cmprime.attpls.com
mpl@pegasus.att.com
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