Easy way of using STL algorithms in C++

Question

I have this code on Win32:

Actor* Scene::GetActor(const char* name)
{
    StringID actorID(name);

    auto actor = find_if(m_actors.begin(), m_actors.end(), [&](Actor* actor){return actor->GetName() == actorID;});
    return  actor != m_actors.end() ? *actor : NULL;
}

Because this couldn't be compiled on iPhone with GCC/LLVM Clang I want to removed C++11 features from it. Is there any other easy way of using STL algorithms without using C++11 features? I don't want to declare simple function like this compare function everywhere in the code.

Not a direct answer to your question (I'll leave that for someone else), but if you're doing lookups often, perhaps you want a different data structure, like `std::map`. — GManNickG, Oct 07 '11 at 06:46
Should we suppose that `m_actors` is something like `std::vector` (it seems so) ? — Matthieu M., Oct 07 '11 at 06:49
Have you tried with Xcode 4.2, which contains Apple LLVM 3.0? — trojanfoe, Oct 07 '11 at 06:54
@trojanfoe/@Roland Illig With LLVM 3.0 with C++0x enabled I have: Parsing error... — Mircea Ispas, Oct 07 '11 at 08:52

Björn Pollex · Accepted Answer · 2011-10-07T09:23:41.787

7

You can try to implement a generic predicate for this, something along these lines (demo here):

template<class C, class T, T (C::*func)() const>
class AttributeEquals {
public:
    AttributeEquals(const T& value) : value(value) {}

    bool operator()(const C& instance) {
        return (instance.*func)() == value;
    }
private:
    const T& value;
};

This would require some more tweaking, since in your case you are working with pointers, but you get the general idea.

edited Oct 07 '11 at 09:23

answered Oct 07 '11 at 07:03

Björn Pollex

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In a similar vein, http://stackoverflow.com/questions/5174115/sorting-a-vector-of-objects-by-a-property-of-the-object/5174694#5174694 – ildjarn Oct 07 '11 at 15:57

score 4 · Answer 2 · answered Oct 07 '11 at 13:36

4

Have you tried using Blocks?

auto actor = find_if(m_actors.begin(), m_actors.end(),
                     ^(Actor* actor){return actor->GetName() == actorID;});

answered Oct 07 '11 at 13:36

Howard Hinnant

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No, but I will try. +1 for this – Mircea Ispas Oct 10 '11 at 10:51

score 2 · Answer 3 · answered Oct 07 '11 at 06:55

Rather than using an anonymous function, you'll have to define and construct a functor. You'll also have to drop the auto keyword.

Actor* Scene::GetActor(const char* name)
{
    StringID actorID(name);
    MyFunctor funct(actorID); // move code from anon function to operator() of MyFunctor
    // Replace InputIterator with something appropriate - might use a shortening typedef
    InputIterator actor = find_if(m_actors.begin(), m_actors.end(), funct);
    return  actor != m_actors.end() ? *actor : NULL;
}

If StringID is your own class, you can make it a functor by defining operator().

Easy way of using STL algorithms in C++

3 Answers3

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