C++ lambda argument list

Question

Here is a bit of code that I'm currently using:

int Engine::getEntityCount(const int objectType)
{
    using namespace std;

    int total = 0;
    for_each(p_entities.begin(), p_entities.end(),
    [&objectType,&total](pair<const int, const list<Entity*>> pair)
    {   
        for_each((pair.second).begin(),(pair.second).end(),
        [&objectType,&total](Entity* &entity)
        {
            if ( entity->getAlive() == true && entity->getObjectType() == objectType )
                ++total;
        });
    });
    return total;
}

I'm getting the following error from intel c++:

error : function "lambda [](Entity *&)->void::operator()" cannot be called with the given argument list c:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\algorithm

I'm having difficulty understanding what's wrong here. Does anyone have any ideas?

Is this really the most elegant way to code a loop over a container? If you want to be cutting-edge, why not range-based for? — Potatoswatter
– Potatoswatter, Commented Dec 3, 2012 at 6:05
@Potatoswatter You're right. I've just used this method because it seems the vast amount of c++ compilers at the moment support lambda, but not range based for atm. I'm also curious as to why I'm getting this error in the first place. — dk123
– dk123, Commented Dec 3, 2012 at 6:07
@dk123, If you're interested, VS2012 supports ranged-based for. GCC and Clang have since before that. — Qaz
– Qaz, Commented Dec 3, 2012 at 6:08
@Potatoswatter I guess I should give VS2012 a shot. Thanks for the quick replies; they've cleared everything. — dk123
– dk123, Commented Dec 3, 2012 at 6:27

Potatoswatter · Accepted Answer · 2012-12-03 06:07:24Z

2

You're asking for a non-const reference to a pointer to an Entity. The list containing that pointer is const. You must decide between a non-const pointer or a const list.

answered Dec 3, 2012 at 6:07

Potatoswatter

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4 Comments

dk123 Over a year ago

You're right. Which is why I originally had the code as 'const Entity*'. I get this error if I do: error : function "lambda [](const Entity *&)->void::operator()" cannot be called with the given argument list.

Potatoswatter Over a year ago

@dk123 You need Entity *const &

Chris Dodd Over a year ago

@dk123: That gives you a reference to a non-const pointer to a const Entity. You want a reference to a const pointer to a non-const Entity: Entity * const &

dk123 Over a year ago

@Potatoswatter Thanks for the quick replies. I should revise my const usage.

zen-cat · Accepted Answer · 2012-12-03 06:14:46Z

-1

....
    for_each((pair.second).begin(),(pair.second).end(),
    [&objectType,&total](const Entity* entity)
    {
        ....
    });
});

....

answered Dec 3, 2012 at 6:14

zen-cat

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