Vector contains?

This is a discussion on Vector contains? within the C++ Programming forums, part of the General Programming Boards category; Hello, I was just wondering how I would check to see if a vector contains an element. I've been searching ...

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    Vector contains?

    Hello, I was just wondering how I would check to see if a vector contains an element. I've been searching but nothing ever comes up when I google vector contains for C++. Was wondering if someone could let me know. Thanks.

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    Compilers can produce warnings - make the compiler programmers happy: Use them!
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    hey thnx =)

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    so i implemented the vectorFind method like so but then i get this error

    Code:
    Severity and Description	Path	Resource	Location	Creation Time	Id
    /usr/include/c++/4.2/bits/stl_algo.h no match for ‘operator==’ in ‘__first.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = Dependency*, _Container = std::vector<Dependency, std::allocator<Dependency> >]() == __val’		phase1	line 216	1223652736055	499

    here is a chunk of my code

    Code:
    result = find( dependencyList.begin(), dependencyList.end(), d);
    
                if(result == dependencyList.end()){
    			dependencyList.push_back(d);
    			isTrue = true;
                }
                else
                 isTrue = true;

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    So your object doesn't have a "operator==" I suppose?

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    just to clarify

    i should have #include <algorithm> in

    in my header file
    and using namespace std;

    right?

  7. #7
    and the Hat of Guessing tabstop's Avatar
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    That's all fine, I guess. result should be a list<type>::iterator.

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    Cat without Hat CornedBee's Avatar
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    You should never have using namespace std; in a header file. But the find algorithm is in the std namespace.
    All the buzzt!
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    >> result should be a list<type>::iterator. <<
    You mean std::vector<Dependency>::iterator or std::vector<Dependency>::const_iterator, right?

    Also, TaiL, do your items have to be in the vector in a certain order? It might make more sense to use a different container if the order of the items doesn't matter. For example, a set<Dependency> might be more appropriate. It is built to allow you to add items and look them up to see if they exist already. In fact, you can insert an item and it will just fail if it already exists.

  10. #10
    Cat without Hat CornedBee's Avatar
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    The order of dependencies does matter, since apparently he's building a work queue.

    Still, I think in this case I'd use an ADT like a linked hash set. Or build a real graph and do a topological sort.

    Either way, work queues are problematic for parallelization.
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    Quote Originally Posted by Daved View Post
    >> result should be a list<type>::iterator. <<
    You mean std::vector<Dependency>::iterator or std::vector<Dependency>::const_iterator, right?
    yeah thats what i was asking about. Sorry.

    Its actually recommended to use a vector =\ so should i be using std::vector<Dependency>:;const_iterator or std::vector<Dependency>iterator??

  12. #12
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by Daved View Post
    >> result should be a list<type>::iterator. <<
    You mean std::vector<Dependency>::iterator or std::vector<Dependency>::const_iterator, right?
    Yes, you're right. Thank you.

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    I think the name 'isTrue' for a boolean variable is about the worst name you can get. How meaningful is it for itTrue to be true? What can we learn from isTrue being false?
    What exactly is it that is, or is not, true? Now call it that instead!

    Also, if you're doing many of these find operations on a vector then it's likely you'd be better off switching to another container instead such as a std::set.
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