Use imported static functions to build a C++ class

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I imported a dll file named swedll64.dll in main function of a c++ program.

C++

#include<iostream>
#include<math.h>
#include<windows.h>

using namespace  std;

typedef double(*_swe_julday)(int, int, int, double, int);
typedef int(*_swe_calc)(double, int, int, double[], char[]);
typedef void(*_swe_revjul)(double, int, int&, int&, int&, double&);

int main()
{
HINSTANCE hInst = LoadLibrary(L"C:\\swedll64.dll");

_swe_julday swe_julday = reinterpret_cast<_swe_julday>(GetProcAddress(hInst, "swe_julday"));
_swe_calc swe_calc = reinterpret_cast<_swe_calc>(GetProcAddress(hInst, "swe_calc"));
_swe_revjul swe_revjul = reinterpret_cast<_swe_revjul>(GetProcAddress(hInst, "swe_revjul"));
return 0;
}

C#

public class Swisseph
{
    public Swisseph()
    {
    }
    [DllImport("swedll32.dll", CharSet = CharSet.Ansi, EntryPoint = "swe_julday")]
    public extern static double xyz_swe_julday(int year, int month, int day, double hour, int gregflag);
    public static double swe_julday(int year, int month, int day, double hour)
    {
        return xyz_swe_julday(year, month, day, hour, 1);
    }

    [DllImport("swedll32.dll", CharSet = CharSet.Ansi, EntryPoint = "swe_calc_ut")]
    public extern static int xyz_swe_calc_ut(double tjd_ut, int ipl, int iflag, double[] xx, StringBuilder serr);
    public static void swe_calc_ut(double tjd_ut, int ipl, int addFlags, double[] xx)
    {
        StringBuilder serr = new StringBuilder(256);
        int ret = xyz_swe_calc_ut(tjd_ut, ipl, addFlags, xx, serr);
    }

    [DllImport("swedll32.dll", CharSet = CharSet.Ansi, EntryPoint = "swe_close")]
    public extern static void xyz_swe_close();
}

What I have tried:

 how can i build a class for imported methods?in other word where should i put this codes in class ? 
Is there another tricks to do so like Dllimport() and extern in c#(i want to do exact whatever written in  below c# code)?

Posted 17-Aug-19 20:48pm

Wolf216

Updated 19-Aug-19 7:22am

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Rick York · Answer 1 · 2019-08-19T07:23:00

Here is one possibility :

typedef double (*_swe_julday)( int, int, int, double, int );
typedef int    (*_swe_calc)( double, int, int, double[], char[] );
typedef void   (*_swe_revjul)( double, int, int&, int&, int&, double& );

class SWE
{
public:
    static inline _swe_julday  JulDay = nullptr;
    static inline _swe_calc    Calc   = nullptr;
    static inline _swe_revjul  RevJul = nullptr;

    static bool Initialize()
    {
        if( m_Initialized )
           return true;

        HINSTANCE hInst = LoadLibrary( _T( "swedll64.dll" ) );
        if( ! hInst )
            return false;

        JulDay = reinterpret_cast<_swe_julday>( GetProcAddress( hInst, "swe_julday" )  );
        Calc = reinterpret_cast<_swe_calc>( GetProcAddress( hInst, "swe_calc" ) );
        RevJul = reinterpret_cast<_swe_revjul>( GetProcAddress( hInst, "swe_revjul" ) );

        m_Initialized = true;
        return true;
    }

    static bool IsInitialized() const    { return m_Initialized; }

protected:
    static inline bool m_Initialized = false;
};

This might look weird because there is some C++17 stuff in there but it will compile and link with VS17. I tried it. To use this the code would like this:

SWE::Initialize();
SWE::JulDay( int1, int2, int3, double1, int4 );

One thing to note is a class with all static methods and members is essentially the same thing as having those functions and data in a namespace. Even the usage syntax is the same.

KarstenK · Answer 2 · 2019-08-17T23:08:00

You have build a class for it, because the imported function are static or global.

The usage in C# is now

C#

Swisseph.xyz_swe_julday(...);

because you renamed them. It isnt a good idea.

Ofcourse you should consider build some class which are using the functions. Some formatting, checking or buffer providing is very handy.

Use imported static functions to build a C++ class

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