Java container types counterparts in C++

Is boost the best bet that i can make use of containers something similar in java
like
SortedMap ArrayList...etc
Thanks
Jack

Boost contains dozens of libraries with widely varying purposes.
The first place to look for containers in C++ is the STL library, which is part of standard C++. They are nothing like Java containers AFAIK, which is great, because C++ is nothing like Java.

STL containers and their approximate Java equivalents:

ArrayList -> std::vector
LinkedList -> std::list
TreeMap -> std::map/std::set/std::multimap/std::multiset
HashMap -> std::unordered_map etc (or boost::unordered_map on older compilers)

C++ also has std::deque, which looks similar to std::vector but is different internally, and some adapters std::stack, std::queue, and std::priority_queue which are not containers but can be used to modify the interface of standard containers if desired.

Boost has some additional containers.

std::map == SortedMap?
are they equivalent?
besides, what is the equivalent for stdext::hash_map in Java?
Thanks
Jack

Quote:

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Originally Posted by lucky6969b

std::map == SortedMap?
are they equivalent?

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Yes and no. Yes, in the sense that the typically expected usage of a std::map would be identical to that of a SortedMap. No, because the details of their interfaces are different, and in fact std::map is a concrete class template whereas SortedMap is an interface construct.

Quote:

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Originally Posted by lucky6969b

what is the equivalence for stdext::hash_map in Java?

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If the name is any clue, then stdext::hash_map's rough equivalent in Java is obviously HashMap.

In other words, do I need to write extra code to keep it sorted?
Thanks
Jack

Quote:

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Originally Posted by lucky6969b

In other words, do I need to write extra code to keep it sorted?

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No.

I suggest that you read Josuttis' The C++ Standard Library - A Tutorial and Reference. It is outdated now that the new edition of the C++ standard has been published, but it is still relevant.

Quote:

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Originally Posted by lucky6969b

In other words, do I need to write extra code to keep it sorted?
Thanks
Jack

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You need to provide the key class with an operator<, OR you need to explicitly provide a comparison function defining a strict weak ordering when the map is constructed.

This sort of approach (either explicitly provide a comparator, or use the type's natural operators by default) is used throughout the STL.

Thanks all of you. I think std::map<int, int, comparator> will do the job

If the key is a primitive such as an int, and the natural notion of ordering is sufficient, then there is no need to do anything special to keep the container sorted.

One thing to watch out for: If you are using a string as the key, it must be a std::string or other string class defining operator< lexicographically. C-style strings, which are essentially just char arrays, will *not* provide the expected behavior when used as map keys (only the pointer values will be compared).

I wonder how to write a comparator with std::string as the key

Code:

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struct Comparator
{
    int operator() (const std::string& str1, const std::string& str2)
    {
          // Any ideas?
    }
};

std::map<std::string, int, Comparator> m_SortedMap;

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Thanks
Jack

Since you presumably do not want to use the default "less than" comparison for std::string as provided by the overloaded operator<, how you do want to compare the strings? That is central to implementing this "less than" comparison function.

I'd like to have it in the ascending order.
BTW how do we get the first item out of an ordered std::set?
I tried m_Set[0] and we can't use begin() since it returns an iterator
Thanks a lot
Jack

Quote:

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Originally Posted by lucky6969b

I'd like to have it in the ascending order.

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Then you don't need a special comparator since operator< works.

Quote:

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Originally Posted by lucky6969b

BTW how do we get the first item out of an ordered std::set?
I tried m_Set[0] and we can't use begin() since it returns an iterator

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begin() returns an iterator to the first element, if it exists.

You mean str1 < str2;?
:)
Thanks
Jack

Quote:

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Originally Posted by lucky6969b

You mean str1 < str2;?

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No, I mean that you can just write:

Code:

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std::map<std::string, int> m_SortedMap;

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Quote:

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Originally Posted by lucky6969b

we can't use begin() since it returns an iterator

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Just dereference the iterator like you would a pointer.