Question

I have a dll created in c++ which exports function using the .def file.The function is written as follows:

__declspec(dllexport) int __stdcall MethodA(int par1,int par2,char *par3)
{....} 

and then the method is declared in the .def file as

MethodA       @1

Now my question is how can I use this method in my C# application ?
I tried adding the dll file as a reference in my C# application and I get the following message

"A reference to the filename.dll could not be added please make sure that the file is accessible and that the file is a valid assembly or COM component."

Edit:
After readings the comments posted here. I am attempting to use the file in the following manner

 [DllImport("C:\\Filename.dll")]
        public static extern int MethodA(int par1,int par2,String par3);

and the I am using it as such

 MethodA(1,2,"SomeString);

This is the error I am getting

An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B)

Answer 1

While you did fine AFAIK on the C++ side, you need to do more on the C# side, You need to create a C# method declaration as something like this:

[DllImport ("your_dll_name")]
extern int MethodA (int par1, int par2);

Decorate with static, unsafe etc. as desired and needed.