Measuring virtual function call cost

C++ version See stopwatch

C++, SECURESCL 0, vector of function pointers, __fastcall

//#define FCALLTYPE 
//#define FCALLTYPESTR "__cdecl"

#define FCALLTYPE __fastcall
#define FCALLTYPESTR "__fastcall"

typedef void  (FCALLTYPE *SumPF)(int &);
void FCALLTYPE OddSum(int &s) { s += 1; }
void FCALLTYPE EvenSum(int &s) { s += 2; }

int main()
{
    using namespace std;
    
    vector<SumPF> v;
    v.push_back(&OddSum);
    v.push_back(&EvenSum);

    Stopwatch sw;
    sw.Start();

    int sum = 0;
    const int maxit = 100000000;
    for (int i = 0; i < maxit; ++i)
    {
        vector<SumPF>::iterator it = v.begin();
        for (; it != v.end(); ++it)
        {
            (*it)(sum);
        }
    }
    
    sw.Stop();
 
    cout << "/**C++, _SECURE_SCL 0, vector of function pointers, " << FCALLTYPESTR << "*/" << endl;
    cout << "iterations =" << maxit << endl;
    cout << "sum        =" << sum << endl;
    cout << "Elapsed    =" << sw << endl;    
    cout << "Average    ="  << sw.GetElapsedMilliseconds() / double(maxit) << " milliseconds/call";    
    cin.get();
}

C++, SECURESCL 0, direct base class call

#define FCALLTYPE 
#define FCALLTYPESTR "__cdecl"

//#define FCALLTYPE __fastcall
//#define FCALLTYPESTR "__fastcall"


struct Base {
  virtual void FCALLTYPE Sum(int &s) = 0;
  virtual ~Base(){}
};

struct Odd : public Base {
  void FCALLTYPE Sum(int &s) { s += 1; }
};

struct Even : public Base {
  void FCALLTYPE Sum(int &s) { s += 2; }
};


int main()
{
    using namespace std;
    Base* podd(new Odd());
    Base* peven(new Even());
    
    Stopwatch sw;
    sw.Start();

    int sum = 0;
    const int maxit = 100000000;
    for (int i = 0; i < maxit; ++i)
    {
      podd->Sum(sum);
      peven->Sum(sum);
    }
    
    sw.Stop();
    
    cout << "/**C++, _SECURE_SCL 0, direct base class call, " << FCALLTYPESTR << "*/" << endl;
    cout << "iterations =" << maxit << endl;
    cout << "sum        =" << sum << endl;
    cout << "Elapsed    =" << sw << endl;    
    cout << "Average    ="  << sw.GetElapsedMilliseconds() / double(maxit) << " milliseconds/call";

    cin.get();

    delete podd;
    delete peven;
}

C++, SECURESCL 0, vector base class call

//#define FCALLTYPE 
//#define FCALLTYPESTR "__cdecl"

#define FCALLTYPE __fastcall
#define FCALLTYPESTR "__fastcall"


struct Base {
  virtual void FCALLTYPE Sum(int &s) = 0;
  virtual ~Base(){}
};

struct Odd : public Base {
  void FCALLTYPE Sum(int &s) { s += 1; }
};

struct Even : public Base {
  void FCALLTYPE Sum(int &s) { s += 2; }
};


int main()
{
    using namespace std;
    
    vector<Base*> v;
    v.push_back(new Odd());
    v.push_back(new Even());

    Stopwatch sw;
    sw.Start();

    int sum = 0;
    const int maxit = 100000000;
    for (int i = 0; i < maxit; ++i)
    {
        vector<Base*>::iterator it = v.begin();
        for (; it != v.end(); ++it)
        {
            (*it)->Sum(sum);
        }
    }
    
    sw.Stop();
    
    cout << "/**C++, _SECURE_SCL 0, vector base class call, " << FCALLTYPESTR << "*/" << endl;
    cout << "iterations =" << maxit << endl;
    cout << "sum        =" << sum << endl;
    cout << "Elapsed    =" << sw << endl;    
    cout << "Average    ="  << sw.GetElapsedMilliseconds() / double(maxit) << " milliseconds/call";

    
    for (vector<Base*>::iterator it = v.begin(); it != v.end(); ++it)
    {
        delete *it;
    }
    cin.get();
}

C# base call

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;

namespace ConsoleApplication1
{

    abstract class Base
    {
        public abstract void Sum(ref int s);
    };

    class Odd : Base
    {
        public override void Sum(ref int s) { s += 1; }
    };

    class Even : Base
    {
        public override void Sum(ref int s) { s += 2; }
    };

    class Program
    {
        static void Main(string[] args)
        {

            List<Base> list = new List<Base>();
            list.Add(new Odd());
            list.Add(new Even());

            Stopwatch sw = new Stopwatch();
            sw.Start();

            int sum = 0;
            const int maxit = 100000000;
            for (int i = 0; i < maxit; ++i)
            {
                for (int k = 0; k < list.Count; k++)
                {
                    list[k].Sum(ref sum);
                }
            }

            sw.Stop();

            Console.WriteLine("iterations : {0}", maxit);
            Console.WriteLine("sum        : {0}", sum);
            Console.WriteLine("Elapsed    : {0}", sw.ElapsedMilliseconds);
            Console.WriteLine("Average    : {0}", sw.ElapsedMilliseconds / (double)maxit);
            Console.Read();
        }
    }
}

C# list ```cpp

using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Diagnostics;

namespace ConsoleApplication1 {

abstract class Base
{
    public abstract void Sum(ref int s);
};

class Odd : Base
{
    public override void Sum(ref int s) { s += 1; }
};

class Even : Base
{
    public override void Sum(ref int s) { s += 2; }
};

class Program
{
    static void Main(string[] args)
    {
        Base odd = new Odd();
        Base even = new Even();

        Stopwatch sw = new Stopwatch();
        sw.Start();

        int sum = 0;
        const int maxit = 100000000;
        for (int i = 0; i < maxit; ++i)
        {
            odd.Sum(ref sum);
            even.Sum(ref sum);
        }

        sw.Stop();

        Console.WriteLine("iterations : {0}", maxit);
        Console.WriteLine("sum        : {0}", sum);
        Console.WriteLine("Elapsed    : {0}", sw.ElapsedMilliseconds);
        Console.WriteLine("Average    : {0}", sw.ElapsedMilliseconds / (double)maxit);
        Console.Read();
    }
}

} ```

C++, SECURESCL 0, direct base class call, __cdecl iterations =100000000 sum =300000000 Elapsed =1695 ms (stopped) Average =1.695e-005 milliseconds/call C++, SECURESCL 0, direct base class call, __fastcall iterations =100000000 sum =300000000 Elapsed =769 ms (stopped) Average =7.69e-006 milliseconds/call C++, SECURESCL 0, vector of function pointers, __cdecl iterations =100000000 sum =300000000 Elapsed =2653 ms (stopped) Average =2.653e-005 milliseconds/call C++, SECURESCL 0, vector of function pointers, __fastcall iterations =100000000 sum =300000000 Elapsed =2549 ms (stopped) Average =2.549e-005 milliseconds/call

C++, SECURESCL 0, vector base class call, __cdecl iterations =100000000 sum =300000000 Elapsed =3424 ms (stopped) Average =3.424e-005 milliseconds/call C++, SECURESCL 0, vector base class call, __fastcall iterations =100000000 sum =300000000 Elapsed =3320 ms (stopped) Average =3.32e-005 milliseconds/call C++, SECURESCL 0, vector base class call, __fastcall, __fastcall in project config iterations =100000000 sum =300000000 Elapsed =3078 ms (stopped) Average =3.078e-005 milliseconds/call

C# base call iterations : 100000000 sum : 300000000 Elapsed : 984 Average : 9,84E-06 C# list iterations : 100000000 sum : 300000000 Elapsed : 3293 Average : 3,293E-05 Brief ``` C++ vector function ptr 2549 C++ vector 3078 C# list 3293 ~ +6%

C++ base call 769 c# base call 984 ~ +27% ```

Thanks Felipe Farion to point out the use of __fastcall VC++ 2008, uses __cdecl by default.