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Nowadays I am looking python source code, and I found both python and C# use hash to implement Dictionary.
The time complexity of hash is O(1) and RBtree is O(lgn), so can anybody tell me the reason why the C++ STL uses RBtree to implement std::map?
Because it has a separate container for hash tables: std::unordered_map<>. Note also that .NET has SortedDictionary<> in addition to Dictionary<>.
The answer can be found in "The Standard C++ Library, A Tutorial and Reference", available online here: http://cs-people.bu.edu/jingbinw/program/The%20C++STL-T&R.pdf.
Short quote explaining:
In general, the whole standard (language and library) is the result of a lot of discussions and
influence from hundreds of people all over the world. For example, the Japanese came up with
important support for internationalization. Of course, mistakes were made, minds were changed,
and people had different opinions. Then, in 1994, when people thought the standard was close to
being finished, the STL was incorporated, which changed the whole library radically. However, to
get finished, the thinking about major extensions was eventually stopped, regardless of how
useful the extension would be. Thus, hash tables are not part of the standard, although they
should be a part of the STL as a common data structure.
Obviously since that time c++ 11 has come out, and since the name map was already taken, and hash_map is a name that was already widely used via common extension libraries (e.g.__gnu_cxx::hash_map), the name unordered_map was chosen for hash maps.
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I am a Java developer trying to learn C++. I have many times read on the internet (including Stack Overflow) that STL is the best collections library that you can get in any language. (Sorry, I do not have any citations for that)
However after studying some STL, I am really failing to see what makes STL so special. Would you please shed some light on what sets STL apart from the collection libraries of other languages and make it the best collection library?
What is so great about the STL ?
The STL is great in that it was conceived very early and yet succeeded in using C++ generic programming paradigm quite efficiently.
It separated efficiently the data structures: vector, map, ... and the algorithms to operate on them copy, transform, ... taking advantage of templates to do so.
It neatly decoupled concerns and provided generic containers with hooks of customization (Comparator and Allocator template parameters).
The result is very elegant (DRY principle) and very efficient thanks to compiler optimizations so that hand-generated algorithms for a given container are unlikely to do better.
It also means that it is easily extensible: you can create your own container with the interface you wish, as long as it exposes STL-compliant iterators you'll be able to use the STL algorithms with it!
And thanks to the use of traits, you can even apply the algorithms on C-array through plain pointers! Talk about backward compatibility!
However, it could (perhaps) have been better...
What is not so great about the STL ?
It really pisses me off that one always have to use the iterators, I'd really stand for being able to write: std::foreach(myVector, [](int x) { return x+1;}); because face it, most of the times you want to iterate over the whole of the container...
But what's worse is that because of that:
set<int> mySet = /**/;
set<int>::const_iterator it = std::find(mySet.begin(), mySet.end(), 1005); // [1]
set<int>::const_iterator it = mySet.find(1005); // [2]
[1] and [2] are carried out completely differently, resulting in [1] having O(n) complexity while [2] has O(log n) complexity! Here the problem is that the iterators abstract too much.
I don't mean that iterators are not worthy, I just mean that providing an interface exclusively in terms of iterators was a poor choice.
I much prefer myself the idea of views over containers, for example check out what has been done with Boost.MPL. With a view you manipulate your container with a (lazy) layer of transformation. It makes for very efficient structures that allows you to filter out some elements, transform others etc...
Combining views and concept checking ideas would, I think, produce a much better interface for STL algorithms (and solve this find, lower_bound, upper_bound, equal_range issue).
It would also avoid common mistakes of using ill-defined ranges of iterators and the undefined behavior that result of it...
It's not so much that it's "great" or "the best collections library that you can get in *any* language", but it does have a different philosophy to many other languages.
In particular, the standard C++ library uses a generic programming paradigm, rather than an object-oriented paradigm that is common in languages like Java and C#. That is, you have a "generic" definition of what an iterator should be, and then you can implement the function for_each or sort or max_element that takes any class that implements the iterator pattern, without actually having to inherit from some base "Iterator" interface or whatever.
What I love about the STL is how robust it is. It is easy to extend it. Some complain that it's small, missing many common algorithms or iterators. But this is precisely when you see how easy it is to add in the missing components you need. Not only that, but small is beautiful: you have about 60 algorithms, a handful of containers and a handful of iterators; but the functionality is in the order of the product of these. The interfaces of the containers remain small and simple.
Because it's fashion to write small, simple, modular algorithms it gets easier to spot bugs and holes in your components. Yet, at the same time, as simple as the algorithms and iterators are, they're extraordinarily robust: your algorithms will work with many existing and yet-to-be-written iterators and your iterators work with many existing and yet-to-be-written algorithms.
I also love how simple the STL is. You have containers, you have iterators and you have algorithms. That's it (I'm lying here, but this is what it takes to get comfortable with the library). You can mix different algorithms with different iterators with different containers. True, some of these have constraints that forbid them from working with others, but in general there's a lot to play with.
Niklaus Wirth said that a program is algorithms plus data-structures. That's exactly what the STL is about. If Ruby and Python are string superheros, then C++ and the STL are an algorithms-and-containers superhero.
STL's containers are nice, but they're not much different than you'll find in other programming languages. What makes the STL containers useful is that they mesh beautifully with algorithms. The flexibility provided by the standard algorithms is unmatched in other programming languages.
Without the algorithms, the containers are just that. Containers. Nothing special in particular.
Now if you're talking about container libraries for C++ only, it is unlikely you will find libraries as well used and tested as those provided by STL if nothing else because they are standard.
The STL works beautifully with built-in types. A std::array<int, 5> is exactly that -- an array of 5 ints, which consumes 20 bytes on a 32 bit platform.
java.util.Arrays.asList(1, 2, 3, 4, 5), on the other hand, returns a reference to an object containing a reference to an array containing references to Integer objects containing ints. Yes, that's 3 levels of indirection, and I don't dare predict how many bytes that consumes ;)
This is not a direct answer, but as you're coming from Java I'd like to point this out. By comparison to Java equivalents, STL is really fast.
I did find this page, showing some performance comparisons. Generally Java people are very touchy when it comes to performance conversations, and will claim that all kinds of advances are occurring all the time. However similar advances are also occurring in C/C++ compilers.
Keep in mind that STL is actually quite old now, so other, newer libraries may have specific advantages. Given the age, its' popularity is a testament to how good the original design was.
There are four main reasons why I'd say that STL is (still) awesome:
Speed
STL uses C++ templates, which means that the compiler generates code that is specifically tailored to your use of the library. For example, map will automagically generate a new class to implement a map collection of 'key' type to 'value' type. There is no runtime overhead where the library tries to work out how to efficiently store 'key' and 'value' - this is done at compile time. Due to the elegant design some operations on some types will compile down to single assembly instructions (e.g. increment integer-based iterator).
Efficiency
The collections classes have a notion of 'allocators', which you can either provide yourself or use the library-provided ones which allocate only enough storage to store your data. There is no padding nor wastage. Where a built-in type can be stored more efficiently, there are specializations to handle these cases optimally, e.g. vector of bool is handled as a bitfield.
Exensibility
You can use the Containers (collection classes), Algorithms and Functions provided in the STL on any type that is suitable. If your type can be compared, you can put it into a container. If it goes into a container, it can be sorted, searched, compared. If you provide a function like 'bool Predicate(MyType)', it can be filtered, etc.
Elegance
Other libraries/frameworks have to implement the Sort()/Find()/Reverse() methods on each type of collection. STL implements these as separate algorithms that take iterators of whatever collection you are using and operate blindly on that collection. The algorithms don't care whether you're using a Vector, List, Deque, Stack, Bag, Map - they just work.
Well, that is somewhat of a bold claim... perhaps in C++0x when it finally gets a hash map (in the form of std::unordered_map), it can make that claim, but in its current state, well, I don't buy that.
I can tell you, though, some cool things about it, namely that it uses templates rather than inheritance to achieve its level of flexibility and generality. This has both advantages and disadvantages; a disadvantage is that lots of code gets duplicated by the compiler, and any sort of dynamic runtime typing is very hard to achieve; however, a key advantage is that it is incredibly quick. Because each template specialization is really its own separate class generated by the compiler, it can be highly optimized for that class. Additionally, many of the STL algorithms that operate on STL containers have general definitions, but have specializations for special cases that result in incredibly good performance.
STL gives you the pieces.
Languages and their environments are built from smaller component pieces, sometimes via programming language constructs, sometimes via cut-and-paste. Some languages give you a sealed box - Java's collections, for instance. You can do what they allow, but woe betide you if you want to do something exotic with them.
The STL gives you the pieces that the designers used to build its more advanced functionality. Directly exposing the iterators, algorithms, etc. give you an abstract but highly flexible way of recombining core data structures and manipulations in whatever way is suitable for solving your problem. While Java's design probably hits the 90-95% mark for what you need from data structures, the STL's flexibility raises it to maybe 99%, with the iterator abstraction meaning you're not completely on your own for the remaining 1%.
When you combine that with its speed and other extensibility and customizabiltiy features (allocators, traits, etc.), you have a quite excellent package. I don't know that I'd call it the best data structures package, but certainly a very good one.
Warning: percentages totally made up.
Unique because it
focuses on basic algorithms instead of providing ready-to-use solutions to specific application problems.
uses unique C++ features to implement those algorithms.
As for being best... There is a reason why the same approach wasn't (and probably won't) ever followed by any other language, including direct descendants like D.
The standard C++ library's approach to collections via iterators has come in for some constructive criticism recently. Andrei Alexandrescu, a notable C++ expert, has recently begun working on a new version of a language called D, and describes his experiences designing collections support for it in this article.
Personally I find it frustrating that this kind of excellent work is being put into yet another programming language that overlaps hugely with existing languages, and I've told him so! :) I'd like someone of his expertise to turn their hand to producing a collections library for the so-called "modern languages" that are already in widespread use, Java and C#, that has all the capabilities he thinks are required to be world-class: the notion of a forward-iterable range is already ubiquitous, but what about reverse iteration exposed in an efficient way? What about mutable collections? What about integrating all this smoothly with Linq? etc.
Anyway, the point is: don't believe anyone who tells you that the standard C++ way is the holy grail, the best it could possibly be. It's just one way among many, and has at least one obvious drawback: the fact that in all the standard algorithms, a collection is specified by two separate iterators (begin and end) and hence is clumsy to compose operations on.
Obviously C++, C#, and Java can enter as many pissing contests as you want them to. The clue as to why the STL is at least somewhat great is that Java was initially designed and implemented without type-safe containers. Then Sun decided/realised people actually need them in a typed language, and added generics in 1.5.
You can compare the pros and cons of each, but as to which of the three languages has the "greatest" implementation of generic containers - that is solely a pissing contest. Greatest for what? In whose opinion? Each of them has the best libraries that the creators managed to come up with, subject to other constraints imposed by the languages. C++'s idea of generics doesn't work in Java, and type erasure would be sub-standard in typical C++ usage.
The primary thing is, you can use templates to make using containers switch-in/switch-out, without having to resort to the horrendous mess that is Java's interfaces.
If you fail to see what usage the STL has, I recommend buying a book, "The C++ Programming Language" by Bjarne Stroustrup. It pretty much explains everything there is about C++ because he's the dude who created it.
I've been programming c++ for about a year now and when i'm looking about i see lots of references to STL.
Can some one please tell me what it does?
and the advantages and disadvantageous of it?
also what does it give me over the borlands VCL or MFC?
thanks
It's the C++ standard library that gives you all sorts of very useful containers, strings, algorithms to manipulate them with etc.
The term 'STL' is outdated IMHO, what used to be the STL has become a large part of the standard library for C++.
If you are doing any serious C++ development, you will need to be familiar with this library and preferably the boost library. If you are not using it already, you're probably working at the wrong level of abstraction or you're constraining yourself to a small-ish subset of C++.
STL stands for Standard Template Library. This was a library designed mainly by Stepanov and Lee which was then adopted as part of the C++ Standard Library. The term is gradually becoming meaningless, but covers these parts of the Standard Library:
containers (vectors, maps etc.)
iterators
algorithms
If you call yourself a C++ programmer, you should be familiar with all of these concepts, and the Standard Library implementation of them.
The STL is the Standard Template Library. Like any library it's a collection of code that makes your life easier by providing well tested, robust code for you to re-use.
Need a collection (map, list, vector, etc) they're in the STL
Need to operate on a collection (for_each, copy, transform, etc,) they're in the STL
Need to do I/O, there's classes for that.
Advantages
1, You don't have to re-implement standard containers (cus you'll get it wrong anyway)
Read this book by Nicolai M.Josuttis to learn more about the STL, it's the best STL reference book out there.
It provides common useful tools for the programmer! Iterators, algorithms, etc. Why re-invent the wheel?
"advantages and disadvantageous" compared to what? To writing all that code yourself? Is not it obvious? It has great collections and tools to work with them
Wikipedia has a good overview: http://en.wikipedia.org/wiki/Standard_Template_Library
The STL fixes one big deficiency of C++ - the lack of a standard string type. This has cause innumerable headaches as there have been thousands of string implementations that don't work well together.
It stands for standard template library
It is a set of functions and class that are there to save you a lot of work.
They are designed to use templates, which is where you define a function, but with out defining what data type it will work on.
for example, vector more or less lets you have dynamic arrays. when you create an instance of it, you say what type you want it to work for. This can even be your own data type (class).
Its a hard thing to think about, but it is hugely powerful and can save you loads of time.
Get reading up on it now! You want regret it.
It gives you another acronym to toss around at cocktail parties.
Seriously, check the intro docs starting e.g. with the Wikipedia article on STL.
The STL has Iterators. Sure, collections and stuff are useful, but the power iterators is gigantic, and, in my humble opinion, makes the rest pale in comparison.
I hear a lot about boost here and I am beginning to think it could help a lot with my software development. More so in concurrency and memory management in my particular case as we have had a lot of bugs in this area.
What are the key language features I need to polish up on to effectively benefit from using boost and to shorten the learning curve? I have seen that function objects are commonly used so I would probably need to polish up on that.
Additionally, are there any tutorials and 101 resources I can quickly look at to just get a feel and understanding on using boost.
I realise there is a lot boost offers and I have to pick the right tools for the right job but any leads will help.
Related
How to learn boost (no longer valid; HTTP return status 404)
Boost has an unimaginable number of libraries.
Easy ones to get started on are
noncopyable
array
circular_buffer
foreach
operators (one of my personal favorites)
smart_ptr
date_time
More advanced ones include
lambda
bind
iostreams
serialization
threads
Getting used to boost takes time, but I assure you it will make your life much better. Plus, looking at how the boost libraries are coded will help you get better at c++ coding, especially templates.
You mentioned what should you look up before trying boost. I agree that function objects are a great thing to research. Also, make sure to look up about template programming. A common problem to make sure you know is when to use the typename qualifier for dependent types. For the most part, however, the libraries are very well documented, with examples and reference materials.
Learning boost is discussed here. As for language features that are useful? All of them. C++ is a dangerous language to use if you don't know enough of it. RAII, functors/function objects and templates probably cover the most important aspects. Boost is designed similarly to the STL, so knowing your standard library is essential. Boost itself uses a lot of template metaprogramming, but as a library user, you won't often need that (unless you start playing with Boost.MPL)
Bugs related to memory management are a good indicator that it's C++, rather than Boost you need to brush up on. The techniques for handling memory safely are well known, and not specific to Boost. (With the obvious exception of Boost's smart pointers). RAII is probably the most important concept to understand to deal with this kind of issues.
What are the key language features I need to polish up on to effectively benefit from using boost and to shorten the learning curve?
Templates
Functors
Exceptions
STL
Iterators
Algorithms
Containers
... among others.
are there any tutorials and 101 resources I can quickly look at to just get a feel and understanding on using boost.
Boost is well documented. Start here.
There are too many libraries to get lost. I'd say start with something simple, maybe smart pointers or Boost.Test (Unit Test framework) -- which will quickly help you get started. Also, try to think of a problem you cannot solve with the STL easily. Then look up Boost documentation or post here.
If you are comfortable with functional programming look at MPL/Lambda libraries.
The first ting IMO are smart pointers. Integration into new code is simple, and usually not a problem for existing code. They make memory management easy, and work for many other ressources, too.
C++ gives you the power to manage your own memory, smart pointers let you (mostly) wing it when you don't need to.
The second would be - as you mentioned - function objects, they close a big gap within C++ that is traditionally solved through inheritance, which is to strong of a coupling in many cases.
I have only little experience with boost outside these two, but most of the remainder is fairly "situational" - you may or may not need it. Get an overview over the libraries, and see what you need.
boost::any and boost::variant are good of you need a variant data type, with two different approaches.
boost::regex if you need some text parsing.
boost::thread and boost::filesystem help you write portable code. If you already have good platform specific libraries, you might not need them - but they are better than API or C++ level in any case.
Maybe you like my introduction to boost smart pointers, and a rather unorthodox use for them.
Try Björn Karlsson's book: Beyond the C++ Standard Library: An Introduction to Boost. Its pretty straightforward and easy to grasp. I read this after I'd finished Scott Meyers three c++ books (effective series).
After reading Beyond the C++ Standard Library: An Introduction to Boost, I would recommend casually browsing the documentation on boost.org, just to get an idea of what's available. You can do a deep dive into a specific boost library when it looks like a good fit for a particular application.
I think shared_ptr sould be the easiest place to start .
Start using it inplaces of simple pointer or auto_ptr data types.
You can also look into weak_ptr.
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Recently, I've got a dangerous idea into my head after reading this blog post. That idea can be expressed like this:
I don't need most of what the C++ standard library offers. So, why don't I implement a less general, but easier to use version?
As an example, using the STL spits out reams of incomprehensible and mangled compiler errors. But, I don't care about allocators, iterators and the like. So why don't I take a couple of hours and implement an easy to use linked list class, for example?
What I'd like to know from the StackOverflow community is this: what are the dangers, possible disadvantages and possible advantages to "rolling my own" for most of the existing functionality in C++?
Edit: I feel that people have misunderstood me about this idea. The idea was to understand whether I could implement a very small set of STL functionality that is greatly simplified - more as a project to teach me about data structures and the like. I don't propose re-inventing the entire wheel from the ground up, just the part that I need and want to learn about. I suppose what I wanted to figure out is whether the complexity of using the STL warrants the creation of smaller, simpler version of itself.
Re-using boost or similiar.
Most of what I code is for University and we're not allowed to use external libraries. So it's either the C++ standard library, or my own classes.
Objectivity of this question.
This question is not subjective. Nor should it be community Wiki, since it's not a poll. I want concrete arguments that highlight one advantage or one disadvantage that could possibly occur with my approach. Contrary to popular belief, this is not opinion, but based on experience or good logical arguments.
Format.
Please post only one disadvantage or one advantage per answer. This will allow people to evaluate individual ideas instead of all your ideas at once.
And please...
No religious wars. I'm not a fan boy of any language. I use whatever's applicable. For graphics and data compression (what I'm working on at the moment) that seems to be C++. Please constrain your answers to the question or they will be downvoted.
So, why don't I implement a less
general, but easier to use version?
Because you can't. Because whatever else you might say about C++, it is not a simple language, and if you're not already very good at it, your linked list implementation will be buggy.
Honestly, your choice is simple:
Learn C++, or don't use it. Yes, C++ is commonly used for graphics, but Java has OpenGL libraries too. So does C#, Python and virtually every other language. Or C. You don't have to use C++.
But if you do use it, learn it and use it properly.
If you want immutable strings, create your string as const.
And regardless of its underlying implementation, the STL is remarkably simple to use.
C++ compiler errors can be read, but it takes a bit of practice. But more importantly, they are not exclusive to STL code. You'll encounter them no matter what you do, and which libraries you use. So get used to them. And if you're getting used to them anyway, you might as well use STL too.
Apart from that, a few other disadvantages:
No one else will understand your code. If you ask a question on SO about std::vector, or bidirectional iterators, everyone who's reasonably familiar with c++ can answer. If you ask abut My::CustomLinkedList, no one can help you. Which is unfortunate, because rolling your own also means that there will be more bugs to ask for help about.
You're trying to cure the symptom, rather than the cause. The problem is that you don't understand C++. STL is just a symptom of that. Avoiding STL won't magically make your C++ code work better.
The compiler errors. Yes, they're nasty to read, but they're there. A lot of work in the STL has gone into ensuring that wrong use will trigger compiler errors in most cases. In C++ it's very easy to make code that compiles, but doesn't work. Or seems to work. Or works on my computer, but fails mysteriously elsewhere. Your own linked list would almost certainly move more errors to runtime, where they'd go undetected for a while, and be much harder to track down.
And once again, it will be buggy. Trust me. I've seen damn good C++ programmers write a linked list in C++ only to uncover bug after bug, in obscure border cases. And C++ is all border cases. Will your linked list handle exception safety correctly? Will it guarantee that everything is in a consistent state if creating a new node (and thereby calling the object type's constructor) throws an exception? That it won't leak memory, that all the appropriate destructors will be called? Will it be as type-safe? Will it be as performant? There are a lot of headaches to deal with when writing container classes in C++.
You're missing out on one of the most powerful and flexible libraries in existence, in any language. The STL can do a lot that would be a pain even with Java's giant bloated class library. C++ is hard enough already, no need to throw away the few advantages it offers.
I don't care about allocators,
iterators and the like
Allocators can be safely ignored. You pretty much don't even need to know that they exist. Iterators are brilliant though, and figuring them out would save you a lot of headaches. There are only three concepts you need to understand to use STL effectively:
Containers: You already know about these. vectors, linked lists, maps, sets, queues and so on.
Iterators: Abstractions that let you navigate a container (or subsets of a container, or any other sequence of value, in memory, on disk in the form of streams, or computed on the fly).
Algorithms: Common algorithms that work on any pair of iterators. You have sort, for_each, find, copy and many others.
Yes, the STL is small compared to Java's library, but it packs a surprising amount of power when you combine the above 3 concepts. There's a bit of a learning curve, because it is an unusual library. But if you're going to spend more than a day or two with C++, it's worth learning properly.
And no, I'm not following your answer format, because I thought actually giving you a detailed answer would be more helpful. ;)
Edit:
It'd be tempting to say that an advantage of rolling your own is that you'd learn more of the language, and maybe even why the STL is one of its saving graces.. But I'm not really convinced it's true. It might work, but it can backfire too.
As I said above, it's easy to write C++ code that seems to work. And when it stops working, it's easy to rearrange a few things, like the declaration order of variables, or insert a bit of padding in a class, to make it seemingly work again. What would you learn from that? Would that teach you how to write better C++? Perhaps. But most likely, it'd just teach you that "C++ sucks". Would it teach you how to use the STL? Definitely not.
A more useful approach might be utilizing the awesome power of StackOverflow in learning STL the right way. :)
Disadvantage: no one but you will use it.
Advantage: In the process of implementing it you will learn why the Standard Library is a good thing.
Advantages: eating your own dogfood. You get exactly what you do.
Disadvantages: eating your own dogfood. Numerous people, smarter than 99 % of us, have spent years creating STL.
I suggested you learn why:
using the STL spits out reams of
incomprehensible and mangled compiler
errors
first
Disadvantage: you may spend more time debugging your class library than solving whatever university task you have in front of you.
Advantage: you're likely to learn a lot!
There is something you can do about the cryptic compiler STL error messages. STLFilt will help simplify them. From the STLFilt Website:
STLFilt simplifies and/or reformats
long-winded C++ error and warning
messages, with a focus on STL-related
diagnostics (and for MSVC 6, it fully
eliminates C4786 warnings and their
detritus). The result renders many of
even the most cryptic diagnostics
comprehensible.
Have a look here and, if you are using VisualC, also here.
I think you should do it.
I'm sure I'll get flambayed for this, but you know, every C++ programmer around here has drunk a little too much STL coolaid.
The STL is a great library, but I know from first hand experience that if you roll your own, you can:
1) Make it faster than the STL for your particular use cases.
2) You'll write a library with just the interfaces you need.
3) You'll be able to extend all the standard stuff. (I can't tell you how much I've wished std::string had a split() method)...
Everyone is right when they say that it will be a lot of work. Thats true.
But, you will learn a lot. Even if after you write it, you go back to the STL and never use it again, you'll still have learned a lot.
A bit of my experience : Not that long ago I have implemented my own vector-like class because I needed good control on it.
As I needed genericity I made a templated array.
I also wanted to iterate through it not using operator[] but incrementing a pointer like a would do with C, so I don't compute the address of T[i] at each iteration... I added two methods one to return pointer to the allocated memory and another that returns a pointer to the end.
To iterate through an array of integer I had to write something like this :
for(int * p = array.pData(); p != array.pEnd(); ++p){
cout<<*p<<endl;
}
Then when I start to use vectors of vectors I figure out that when it was possible a could allocate a big bloc of memory instead of calling new many times. At this time I add an allocator to the template class.
Only then I notice that I had wrote a perfectly useless clone of std::vector<>.
At least now I know why I use STL...
Disadvantage : IMHO, reimplimenting tested and proven libraries is a rabit hole which is almost garanteed to be more trouble than it's worth.
Another Disadvantage:
If you want to get a C++ job when you're finished with University, most people who would want to recruit you will expect that you are familiar with the Standard C++ library. Not necessarily intimately familiar to the implementation level but certainly familiar with its usage and idioms. If you reimplement the wheel in form of your own library, you'll miss out on that chance. This is nonwithstanding the fact that you will hopefully learn a lot about library design if you roll your own, which might earn you a couple of extra brownie points depending on where you interview.
Disadvantage:
You're introducing a dependency on your own new library. Even if that's sufficient, and your implementation works fine, you still have a dependency. And that can bite you hard with code maintenance. Everyone else (including yourself, in a year's time, or even a month's) will not be familiar with your unique string behavior, special iterators, and so on. Much effort will be needed just to adapt to the new environment before you could ever start refactoring/extending anything.
If you use something like STL, everyone will know it already, it's well understood and documented, and nobody will have to re-learn your custom throwaway environment.
You may be interested in EASTL, a rewrite of the STL Electronic Arts documented a while back. Their design decisions were mostly driven by the specific desires/needs in multiplatform videogame programming. The abstract in the linked article sums it up nicely.
Advantage
If you look into MFC, you'll find that your suggestion already is used in productive code - and has been so for a long time. None of MFC's collection classes uses the STL.
Why don't you take a look at existing C++ libraries. Back when C++ wasn't quite as mature, people often wrote their own libraries. Have a look at Symbian (pretty horrible though), Qt and WxWidgets (if memory serves me) have basic collections and stuff, and there are probably many others.
My opinion is that the complexity of STL derives from the complexity of the C++ language, and there's little you can do to improve on STL (aside from using a more sensible naming convention). I recommend simply switching to some other language if you can, or just deal with it.
Disadvantage : You're university course is probably laid out like this for a reason. The fact that you are irritated enough by it (sarcasm not intended), may indicate you are not getting the paridigm, and will benefit a lot when you have a paradigm shift.
As an example, using the STL spits out
reams of incomprehensible and mangled
compiler errors
The reason for this is essentially C++ templates. If you use templates (as STL does) you will get reams of incomprehensible error messages. So if you implement your own template based collection classes you will not be in any better spot.
You could make non template based containers and store everything as void pointers or some base class e.g. But you would lose compile time type checks and C++ sucks as a dynamic language. It is not as safe to do this as it would be in e.g. Objective-C, Python or Java. One of the reasons being that C++ does not have a root class for all classes to all introspection on all objects and some basic error handling at runtime. Instead your app would likely crash and burn if you were wrong about the type and you would not be given any clues to what went wrong.
Disadvantage: reimplementing all of that well (that is, at a high level of quality) will certainly take a number of great developers a few years.
what are the dangers, possible disadvantages and possible advantages to "rolling my own" for most of the existing functionality in C++?
Can you afford and possibly justify the amount of effort/time/money spent behind reinventing the wheel?
Re-using boost or similiar.
Rather strange that you cannot use Boost. IIRC, chunks of contribution come in from people related to/working in universities (think Jakko Jarvi). The upsides of using Boost are far too many to list here.
On not 'reinventing the wheel'
Disadvantage: While you learn a lot, you also set yourself back, when you come to think of what your real project objectives are.
Advantage: Maintenance is easier for the folks who are going to inherit this.
STL is very complex because it needs to be for a general purpose library.
Reasons why STL is the way it is:
Based on interators so standard algorithms only need a single implementation for different types of containers.
Designed to behave properly in the face of Exceptions.
Designed to be 'thread' safe in multi threaded applications.
In a lot of applications however you really have enough with the following:
string class
hash table for O(1) lookups
vector/array with sort / and binary search for sorted collections
If you know that:
Your classes do not throw exceptions on construction or assignment.
Your code is single threaded.
You will not use the more complex STL algorithms.
Then you can probably write your own faster code that uses less memory and produces simpler compile/runtime errors.
Some examples for faster/easier without the STL:
Copy-on-Write string with reference counted string buffer. (Do not do this in a multi-threaded environment since you would need to lock on the reference count access.)
Use a good hash table instead of the std::set and std::map.
'Java' style iterators that can be passed around as a single object
Iterator type that does not need to know the type of the container (For better compile time decoupling of code)
A string class with more utility functions
Configurable bounds checking in your vector containers. (So not [] or .at but the same method with a compile or runtime flag for going from 'safe' to 'fast' mode)
Containers designed to work with pointers to objects that will delete their content.
It looks like you updated the question so now there are really two questions:
What should I do if I think the std:: library is too complex for my needs?
Design your own classes that internally use relevant std:: library features to do the "heavy lifting" for you. That way you have less to get wrong, and you still get to invent your own coding interface.
What should I do if I want to learn how data structures work?
Design your own set of data structure classes from the ground up. Then try to figure out why the standard ones are better.