Calling C++ Dll From C#

C++ is powerful language. Generally, C++ can do everything from lower level operations to higher level GUI controls.  There are some higher level programming languages(like C#, Java etc) which can create a very good GUI with less effort. So, generally, C++ is being used in  low level intensive processing or memory level operations which is very fast as compared to other higher level programming language. We can fully use the power of C++ pointers.

So, the general convention is we design the GUI related things in C# and the intensive processing lower level tasks are assigned to C++. We develop all the require functions in C++ and then generate a dynamic link library which contains all the methods. If you are using Microsoft Visual Studio, creating dlls is not a big deal.

After you have a dll file, I am gonna expain how this dll can be used in C#. You may have already noticed that in C# project, the C++ dlls can not be added as reference. So, we have to do something lengthy to get them work. I have studied two P/Invoke methods that are working perfectly:

Before I start the method, I have sample C++ files(Sample.h,Sample.cpp) under the project "CppProject".

//Sample.h

#define DllExport __declspec(dllexport)
extern "C" DllExport double findSquareRoot(double);





//Sample.cpp

double findSquareRoot(double value){
return sqrt(value);
}


Method 1:  Simple Method                   
                  (i) Create a C# file Test.cs under the project CsharpProject and include the following content:
                   //Test.cs
        using System.Runtime.InteropServices;
        namespace CsharpProject
        {
        [DllImport(@"CppProject.dll")]
        public static extern double findSquareRoot(double value);
        class Test{                     
        private void displayRoot(double value)
        {
         double root=findSquareRoot(value);
         System.Console.WriteLine("Square root is "+root);
         }
        }
       }


      (ii)Create dynamic link library CppProject.dll from Microsoft Visual Studio.    


                (iii)Copy the dll in the bin/debug or bin/release folder of the project and compile the C# project. 
 (Note: if you get an error message "PInvokeStackImbalance was detected", then you go to Debug-> Exceptions. Then expand "Managed Debugging Assistants", and disselect "PInvokeStackImbalance". Then it will work)


Method 2: Lengthy Method:
               (i) Create a C# file Test.cs under the project CsharpProject and include the following content: 

               //Test.cs
      using System.Runtime.InteropServices;
      namespace CsharpProject
      {

      static class NativeMethods
      {
       [DllImport("kernel32.dll")]
       public static extern IntPtr LoadLibrary(string dllToLoad);
       [DllImport("kernel32.dll")]
        public static extern IntPtr GetProcAddress
             (IntPtr hModule, string procedureName);


       [DllImport("kernel32.dll")]
        public static extern bool FreeLibrary(IntPtr hModule);
       }
   
       class Test
       {
        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
        private delegate double findSquareRoot(double value);
        IntPtr pDll =           NativeMethods.LoadLibrary(@"CppProject.dll");
        IntPtr pAddressOfFunctionToCall = NativeMethods.GetProcAddress(pDll, "findSquareRoot");
        findSquareRoot squareRoot = 
                 ( findSquareRoot)
Marshal.GetDelegateForFunctionPointer(pAddressOfFunctionToCall,
                  typeof( findSquareRoot ));
         private void displayroot(double value)
         {
          double root=squareRoot(value);
          System.Console.WriteLine("Square root is "+root);
          }
        
        }
  


       (ii)Create dynamic link library CppProject.dll from Microsoft Visual Studio.    
        (iii)Copy the dll in the bin/debug or bin/release folder of the project and compile the C# project. 

             
How to Test?

To test, you go to Program.cs file which contains the startup Main functon, and then write the following piece of code in the Main function:
   new Test().displayRoot(12.44);
After your run, you will get the square root of 12.44 displayed in the console.

I think you got something regarding how C++ dll can be used in C# applications.

Any confusion, contact me (krishna444@gmail.com).

Thanks for reading :)