Need help with class functions

[avadhootp]

So I have an object of class NRG (Normal Rand Genrator) which takes, as an argument to it's constructor, an object of class RG (Rand genrator).

template<typename RG>
class NRG
{
    RG rg;
public:
    NRG(RG r):rg(r){}
    double operator()();
};

An object of this class will return a normal random when it's member function operator()() is called:

template<typename RG>
double class NRG::operator()()
    {
        static int flag = 0;
        static double N2 = 0.0;
        if(flag==0)
        {
            double u1 = (double)rg()/rg.max();
            double u2 = (double)rg()/rg.max();
            double N2 = sqrt(-2*log(u1))*cos(2*PI*u2);
            flag=1;
            return sqrt(-2*log(u1))*sin(2*PI*u2);
        }
        else
        {
            flag=0;
            return N2;
        }
    }

However, when I run this I get an error which says:
C:\Users\avadhoot\Desktop\bb.cpp|69|error: 'template<class RG> class NRG' used without template parameters|
C:\Users\avadhoot\Desktop\bb.cpp|69|error: expected identifier before 'operator'|
C:\Users\avadhoot\Desktop\bb.cpp|69|error: two or more data types in declaration of 'operator()'|
||=== Build failed: 3 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===|

Please help me out!

[LB]

The error is not in the code you have shown. Show the contents of bb.cpp

By the way, I hope you defined your operator()() in the same header as NRG - if not you will have more problems because template classes must have all member definitions that are being used visible to the compiler.

[avadhootp]

#include <iostream>
#include <chrono>
#include <random>
#include <cmath>
#include <fstream>

#define PI 3.14159265

template<typename RG>
class NRG
{
    RG rg;
public:
    NRG(RG r):rg(r){}
    double operator()();
};

template<typename NG>
class SPG
{
    double S0, T, Mu, Vol;
    NG ng;
public:
    SPG(NG n, double Init, double Mat, double Drift, double Sig)
    :ng(n),S0(Init),T(Mat),Mu(Drift),Vol(Sig){}
    double operator()(double dt);
};

template<typename SPG>
double MCEngine(SPG s, double dt, int NumOfSims);

double Expected_Price(double Init, double Mat, double Drift);

int main()
{
    std::mt19937 a(std::chrono::system_clock::now().time_since_epoch().count());
    NRG<std::mt19937> b(a);
    double S=50.0, maturity=1.0, mu=0.1, sig=0.3;
    SPG<NRG<std::mt19937>> c(b, S, maturity, mu, sig);
    double Mean = Expected_Price(S, maturity, mu);
    std::ofstream d("1.csv");
    d<<"dt"<<","<<"WeakError"<<"\n";
    for(int i=5; i<=12; i++)
    {
        double dt = pow(2,-i);
        d<<dt<<","<<std::abs(MCEngine(c, dt, 50000)-Expected_Price(S, maturity, mu))<<"\n";
    }
    d.close();
    return 0;
}

double Expected_Price(double Init, double Mat, double Drift)
{
    return Init*exp(Mat*Drift);
}

template<typename SPG>
double MCEngine(SPG s, double dt, int NumOfSims)
{
    double sum=0.0;
    for(int i=0; i<NumOfSims; i++)
    {
        sum+=s(dt);
    }
    return (double)sum/NumOfSims;
}

template<typename RG>
double class NRG::operator()()
    {
        static int flag = 0;
        static double N2 = 0.0;
        if(flag==0)
        {
            double u1 = (double)rg()/rg.max();
            double u2 = (double)rg()/rg.max();
            double N2 = sqrt(-2*log(u1))*cos(2*PI*u2);
            flag=1;
            return sqrt(-2*log(u1))*sin(2*PI*u2);
        }
        else
        {
            flag=0;
            return N2;
        }
    }

template<typename NG>
double class SPG::operator()(double dt)
    {
        double t=0.0, s = S0, Mudt = Mu*dt, Volsqdt = Vol*sqrt(dt);
        do
        {
            s *= (1+Mudt+Volsqdt*ng());
            t += dt;
        }while(t<T);
        return s;
    }

Well, the thing is when I define the function within the class body, everything workds just fine. But I think I am missing something when I define the m=functions outside of the class body.

For the sake of clasrity:

RG : AN object of this class will produce a random number
NRG: an object of this class will produce a standard normal
SPG: Stock price generator. An object of this class will produce a stock price.

[LB]

I generally prefer defining things inside the class body because it is harder to make these mistakes and it is less typing. This is your issue:

template<typename RG>
double class NRG/*<RG>*/::operator()()
    {