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 1/15/96 Glass, Graham. "Extending the STL." C++ Report. January, 1996 Whitepaper to use STL with VC++ 4 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 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 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: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 hp.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 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 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 ::size_type (187) CC: "release1.C", line 28: warning: debug.emit_type_entry:typedef node **has no symid_ptr: vector ::const_reference (187) The executable does run and the debugger still works, however. Note that the person evaluating STL 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 , it pulls in all the other dependent includes. It is not explicitly stated, but for C-like arrays, you #include . 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 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