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This is a discussion on sort within the C++ Programming forums, part of the General Programming Boards category; How would I sort a vector of strings by the size of the string? pal is a vector containing strings. ...

  1. #1
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    sort

    How would I sort a vector of strings by the size of the string? pal is a vector containing strings. I call sort using the function greater to sort the strings by size.
    Code:
    psuedocode:
    
    sort(pal.begin(), pal.end(), greater);
    
    .................................
    
    bool greater(string a, string b)
    {
    	int i, j;
    	i = a.size();
    	j = b.size();
    	return i > j;
    }

  2. #2
    C++ Witch laserlight's Avatar
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    How does it not work?

    By the way, you should be passing the strings by const reference in the comparator.
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  3. #3
    The larch
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    The idea is correct.

    You could rename the comparison function to something like longer to describe better what it does (there is already std::greater and it means comparing with > operator) and shorten it just to a single return statement.
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
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  4. #4
    and the Hat of Guessing tabstop's Avatar
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    Just like that?

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    I was getting an error, reference to ‘greater’ is ambiguous, along with several other errors. When I changed greater to longer it works fine. I didn't realize there was already a std::greater. Thanks.

  6. #6
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by swappo
    I was getting an error, reference to ‘greater’ is ambiguous, along with several other errors.
    Ah well, at least now you know that you should post about the problem, including any error messages

    Incidentally, you should consider turning the comparator into a function object:
    Code:
    struct Longer
    {
        bool operator()(const std::string& lhs, const std::string& rhs) const
        {
            return lhs.size() > rhs.size();
        }
    };
    You could easily turn it into a class template too, if you see a need to do so.
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  7. #7
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    Quote Originally Posted by swappo View Post
    I was getting an error, reference to ‘greater’ is ambiguous, along with several other errors. When I changed greater to longer it works fine. I didn't realize there was already a std::greater. Thanks.
    Are you including the <functional> header and using a using namespace std; directive?
    If so, it probably sees your greater() function as well as std::greater and doesn't know which one you're talking about.

    Try renaming your function to longer() as previously suggested, or get rid of using namespace std;
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  8. #8
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by cpjust
    Try renaming your function to longer() as previously suggested, or get rid of using namespace std;
    Or fully qualify the global function as ::greater, but frankly renaming it is the best option even if there was no name collision.
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