How to retrieve the user defined data type into main function

Lost User

Manoj7390 wrote:

Templates and namespaces are very important for my program.

That is most unlikely, and looking at what you have posted you are not using them for any good reason. You should get the code working first without the use of either, and then add them (if they are really necessary) at a later stage.

Use the best guess

Lost User

I think that confirms my comment to you about the use of namespaces and templates.

Use the best guess

Stefan_Lang

Starting at the bottom, your main function doesn't make sense - it's one huge syntax error. Even with all the context and the realisation what this is about (encryption), it's almost impossible to guess what it should do. Obviously you're not familiar with template syntax. Your attempt to invoke a templated function using a templated type is a syntactical mess. Your data structure definitions contain errors related to incomplete or improper template syntax. For that reason, and because you don't really use or need those template parameters, you should really forget about them! Since you claim you do need the template, use a const instead: in most cases, where people think they need a template, a global/static definition works just as well:

const int P = 263;

Start with your struct definition:

struct encrypt_data_t {
EllipticCurve::Point Pa;
FiniteFieldElement c1;
FiniteFieldElement c2;
};

There: no typedef required, no template parameters required. Also, since the definition is within your namespace, no need to explicitely add the prefix "Cryptography::". Next, remove any remaining template parameter definition line in your code: if you always used P as the template parameter name, everything should compile after removing the template <argument list>. Last: fix your main(). I have no idea what your intention is, but you do call a function that returns a struct, and apparently try to assign that struct to an int. That doesn't make sense. Fix it, or at least remove that assignment, so you can find out and fix any remaining syntax errors. Besides, you omitted the return type for main() (always int), and your main didn't return a value. Both should be listed as errors or at the very least as warnings by your compiler. But it's possible your compiler didn't get that far due to it's inability to resolve previous spaghetti template syntax.

Manoj7390

If I delete template parameter, then it is giving so many errors. I will post the full program to you please fix it. I want to return {Pa,c1,c2} from this program to another main() function. Please help me out.

#include <cstdlib>
#include <iostream>
#include <vector>
using std:: cout;
using std:: cin;
using std:: endl;
using namespace std;
#include <math.h>
#include "FiniteFieldElement.hpp"

namespace Cryptography
{
template<int P>
class EllipticCurve
{
public:

            typedef FiniteFieldElement<P> ffe\_t;
             
            class   Point
            {
                friend  class   EllipticCurve<P>;
                typedef FiniteFieldElement<P> ffe\_t;
                ffe\_t  x\_;
                ffe\_t  y\_;
                EllipticCurve    \*ec\_;
                
                void   addDouble(int m, Point& acc)
                {        
                    if ( m > 0 )
                    {       
                        Point r = acc; 
                        for ( int n=0; n < m; ++n )
                        {
                            r += r;     // doubling step                          
                        }
                        acc = r;
                    }        
                }
                
                Point scalarMultiply(int k, const Point& a)
                {
                    Point acc = a;
                    Point res = Point(0,0,\*ec\_);
                    int i = 0, j = 0;
                    int b = k;
                    
                    while( b )
                    {
                        if ( b & 1 )
                        {
                            addDouble(i-j,acc);
                            res += acc;           
                            j = i;  
                        }
                        b >>= 1;
                        ++i;
                    }
                    return res;
                }
                
                void    add(ffe\_t x1, ffe\_t y1, ffe\_t x2, ffe\_t y2, ffe\_t & xR, ffe\_t & yR) const
                {
                                          
                    if ( x1 == 0 && y1 == 0

Stefan_Lang

Without the declaration of the class FiniteFieldElement, and without the error messages, I can't help you. I've successfully compiled that code by using the following dummy declaration:

template
class FiniteFieldElement {
public:
FiniteFieldElement(){}
FiniteFieldElement(int){}
int i() const {return 0;}
operator int() const {return 0;}
};

This means that either there is a problem with the actual class declaration, or you are not using it correctly.

Manoj7390

The code is working fine. I need to return those three variables i.e. {Pa,c1,c2} from that program to another main program. What should i have to do. I have used structure for that but its not working. Please tell how to return a three user defined data type to the main function

Stefan_Lang

Manoj7390 wrote:

The code is working fine.

Now, that is news! From your original posting:

Manoj7390 wrote:

I am getting so many errors

May be you should have been clearer from the start about this...

Stefan_Lang

There can only be one int main(). You have to separate the code that does the calculations from the code that inquires the input. You have plenty of functions that pass values around, so I don't see why there should be a problem passing these values via a function interface.

Manoj7390

how to return those values using structure or by declaring class

Stefan_Lang

Change the struct definition to

template<int P> struct encrypt_data_t {
typename Cryptography::EllipticCurve::Point Pa;
FiniteFieldElement c1;
FiniteFieldElement c2;
} ;

Then call this function like this:

int main(...) {
const int MY_P = 263;
...
encrypt_data_t result = my_encrypt();
...
}

Of course, you also have to fix your function code - the code you posted does not declare half the variables it uses. Or you could just skip that structure and instead pass these values back by reference[^]:

template
void my_encrypt(typename Cryptography::EllipticCurve::Point& Pa,
FiniteFieldElement

& c1, FiniteFieldElement

& c2) {
...
}
int main(...) {
const int MY_P = 263;
typename Cryptography::EllipticCurve::Point Pa;
FiniteFieldElement c1;
FiniteFieldElement c2;
my_encrypt(Pa, c1, c2);
}