Pass function into function using std::bind

Question

I've been working on these functions for the last two days and have my CPU and Wall times working finally after using boost,

The last thorn I just can't get me head around, I'm trying to pass a function with parameters into anther function that returns a value using std::bind,

I'm a student and this is all new to me, learning as I go,

int CA1::binarySearch(vector<int> v, int target)
{

    int top, bottom, middle;
    top = vecSize - 1;
    bottom = 0;

    while (bottom <= top)
    {
        middle = (top + bottom) / 2;
        if (v[middle] == target)
            return  middle;
        else if (v[middle] > target)
            top = middle - 1;
        else
            bottom = middle + 1;
    }
    return -1;
}


double CA1::measure(std::function<void()> function) {
    auto startCpu = boost::chrono::process_real_cpu_clock::now();
    auto startWall = boost::chrono::process_system_cpu_clock::now();

    function();

    auto durationCpu = boost::chrono::duration_cast<boost::chrono::nanoseconds>
        (boost::chrono::process_real_cpu_clock::now() - startCpu);
    auto durationWall = boost::chrono::duration_cast<boost::chrono::nanoseconds>
        (boost::chrono::process_system_cpu_clock::now() - startWall);


    double cpuTime = static_cast<double>(durationCpu.count()) * 0.000001;
    double wallTime = static_cast<double>(durationWall.count()) * 0.000001;

    /*return static_cast<double>(duration.count()) * 0.000001;*/

    cout << "Cpu time " << cpuTime << endl;
    cout << "Wall time " << wallTime << endl;

    return cpuTime;
}

void CA1::DoTests() {

    auto  time = measure(std::bind(binarySearch, vectorUnordered, 2));
}

The error I'm getting is:

error C3867: 'CA1::binarySearch': function call missing argument list; use '&CA1::binarySearch' to create a pointer to member

But from what I've read and the code snippets I've seen by other users my code in DoTests() is correct.

since binarySearch is a non-static member function you need to qualify the name like &CA1::binarySearch, as well as bind an instance of CA1 for which the method will be invoked, e.g. std::bind(&CA1::binarySearch, this, vectorUnordered, 2) — Piotr Skotnicki
– Piotr Skotnicki, Commented Oct 23, 2014 at 19:35

theamk · Accepted Answer · 2014-10-23 19:36:35Z

2

Class functions have explicit 'this' parameter, which needs to passed in as first argument:

measure(std::bind(&CA1::binarySearch, this, vectorUnordered, 2))

answered Oct 23, 2014 at 19:36

theamk

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Community · Accepted Answer · 2017-05-23 10:27:14Z

2

Apparently, binarySearch is a member function of the class CA1 and member functions always have an implicit this parameter. When you use std::bind with a member function you will need to pass this as well (see "Using std::bind with member function, use object pointer or not for this argument?"), but that's not necessarily the best solution...

Does binarySearch need to be a member function? C++ doesn't force you to put everything inside a class and you shouldn't, unless it makes sense to do so. In general, a function that doesn't need access to the class' private members should not be a member function (see "How Non-Member Functions Improve Encapsulation"). Besides, the standard library already has std::binary_search.

edited May 23, 2017 at 10:27

CommunityBot

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answered Oct 23, 2014 at 19:38

Paul Manta

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12 Comments

Johnk Over a year ago

Yes I need access to the private members of the class in binarySearch, I've changed my code, but now I'm getting a new error: see reference to function template instantiation 'std::function<void (void)>::function<std::_Bind<true,int,std::_Pmf_wrap<int (__thiscall CA1::* )(std::vector<int,std::allocator<_Ty>>,int),int,CA1,std::vector<_Ty,std::allocator<_Ty>>,int>,CA1 *const ,std::vector<_Ty,std::allocator<_Ty>> &,int>>(_Fx &&)' being compiled

Johnk Over a year ago

I have to write the binarySearch for an assignment.

Paul Manta Over a year ago

How does DoTests look like now?

Johnk Over a year ago

void CA1::DoTests() { auto time = measure(std::bind(&CA1::binarySearch, this, vectorUnordered, 2)); }

Paul Manta Over a year ago

That seems correct. Is this code similar to what you did?

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