c# - 在 C# 中绑定(bind) C++ dll 时出现 EntryPointNotFoundException

Question

我尝试绑定(bind)一个简单的 c++ dll，如 http://msdn.microsoft.com/en-us/library/ms235636.aspx 所示。在我的 c# 控制台应用程序中，但我在运行时在 dll 中添加了一个 EntryPointNotFoundException。我的测试类是

namespace BindingCppDllExample
{
    public class BindingDllClass
    {
        [DllImport("MathFuncsDll.dll")]
        public static extern double Add(double a, double b);
    }

    public class Program
    {
        public static void Main(string[] args)
        {
            double a = 2.3;
            double b = 3.8;
            double c = BindingDllClass.Add(a, b);

            Console.WriteLine(string.Format("{0} + {1} = {2}", a, b, c));
        }
    }
}

哪里不对？

Answer 1

您可以尝试在类外部声明函数，并使用 extern "C" 导出它们:

标题:

// MathFuncsDll.h
namespace MathFuncs
{
    // Returns a + b
    extern "C" __declspec(dllexport) double Add(double a, double b);

    // Returns a - b
    extern "C" __declspec(dllexport) double Subtract(double a, double b);

    // Returns a * b
    extern "C" __declspec(dllexport) double Multiply(double a, double b);

    // Returns a / b
    // Throws DivideByZeroException if b is 0
    extern "C" __declspec(dllexport) double Divide(double a, double b);
}

实现:

// MyMathFuncs.cpp
#include "MathFuncsDll.h"
#include <stdexcept>

using namespace std;

namespace MathFuncs
{
    double Add(double a, double b)
    {
        return a + b;
    }

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

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

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

        return a / b;
    }
}

调用代码:

namespace BindingCppDllExample
{
    public class BindingDllClass
    {
        [DllImport("MathFuncsDll.dll")]
        public static extern double Add(double a, double b);
    }

    public class Program
    {
        public static void Main(string[] args)
        {
            double a = 2.3;
            double b = 3.8;
            double c = BindingDllClass.Add(a, b);

            Console.WriteLine(string.Format("{0} + {1} = {2}", a, b, c));
        }
    }
}