Question

I have a DLL which contains unmanaged classes with methods. I’m trying to call those methods from C++/CLI.

My reading has lead me to find that P/Invoke is used to do this. However, I can’t seem to find out how to make it work.

In the DLL, the following class is defined:

//Header:
namespace MathFuncs
{
    class MyMathFuncs
    {
    public:
        static __declspec(dllexport) double Add(double a, double b);
        static __declspec(dllexport) double Subtract(double a, double b);
        static __declspec(dllexport) double Multiply(double a, double b);
        static __declspec(dllexport) double Divide(double a, double b);
    };
}

//Source:
namespace MathFuncs
{
    double MyMathFuncs::Add(double a, double b) {
        return a + b;
    }

    double MyMathFuncs::Subtract(double a, double b) {
        return a - b;
    }

    double MyMathFuncs::Multiply(double a, double b) {
        return a * b;
    }

    double MyMathFuncs::Divide(double a, double b) {
        if (b == 0) {
            throw new invalid_argument("b cannot be zero!");
        }
        return a / b;
    }
}

From what I’ve read, the following should declare a method in my C++/CLI code, which I can then call in my code:

class MyMathFuncs {
public:
[DllImport("TestDLL.dll")]
    static double Add(double a, double b);
};

Where “TestDLL.dll” is my DLL.

The error I get is at runtime. It says “Unable to find an entry point named ‘Add’ in DLL ‘TestDLL.dll'”.

What am I doing wrong? I’ve read through the MSDN articles on this, but I don’t understand it.

Thanks in advance for your help!

Answer 1

Did you create a DEF file for your native DLL?

• http://msdn.microsoft.com/en-us/library/d91k01sh(v=vs.80).aspx

Dumpbin may also help. See what the DLL is exporting:

• http://msdn.microsoft.com/en-us/library/c1h23y6c(v=vs.71).aspx
• http://msdn.microsoft.com/en-us/library/30e78zd0(v=vs.71).aspx