for_each function and operator()

This is a discussion on for_each function and operator() within the C++ Programming forums, part of the General Programming Boards category; Hello everyone, I can not find related information in MSDN, so I want to confirm here, that, the implementation of ...

  1. #1
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    for_each function and operator()

    Hello everyone,


    I can not find related information in MSDN, so I want to confirm here, that,

    the implementation of for_each is something like,

    Code:
    template <class A, class B> B for_each (A begin, A end, B Func)
    {
        while (begin != end) Func(*begin++);
        return Func;
    }
    So, operator(*A) of class Func will be invoked? Right?


    thanks in advance,
    George
    Last edited by George2; 12-03-2007 at 06:26 AM.

  2. #2
    C++ Witch laserlight's Avatar
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    the implementation of for_each is something like
    The C++ Standard declares std::for_each() as:
    Code:
    template<class InputIterator, class Function>
    Function for_each(InputIterator first, InputIterator last, Function f);
    The MinGW port of g++ 3.4.5 has an implementation that amounts to:
    Code:
    template<class InputIterator, class Function>
    Function for_each(InputIterator first, InputIterator last, Function f)
    {
        for (; first != last; ++first)
        {
            f(*first);
        }
        return f;
    }
    So, operator(*A) of class Func will be invoked? Right?
    Function::operator(InputIterator::value_type) is the overloaded operator that will be invoked.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  3. #3
    Officially An Architect brewbuck's Avatar
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    So, operator(*A) of class Func will be invoked? Right?
    Actually, operator()(typename std::iterator_traits<A>::value_type) will be invoked.

  4. #4
    The larch
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    I seems to me that Func doesn't necessarily have to be a function object but might be a simple function with a suitable prototype.
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  5. #5
    C++ Witch laserlight's Avatar
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    I seems to me that Func doesn't necessarily have to be a function object but might be a simple function with a suitable prototype.
    Yes, that is true.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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