C＃：DLLImport-找不到DLL异常

Question

假设我想从ac＃代码中调用c ++函数，遇到以下问题：

情况1：

class abc
{
private :
    int a ;

public :
    int  getValue()
    {
        return 100;
    }
};

int GetCounter()
{
    abc* p = new abc();

    int i = p->getValue();
    return i;
}

从C＃调用函数时，这种情况会抛出DLL找不到异常。

情况2：

int GetCounter()
{
    int i = 333;
    return i;
}

从C＃调用函数的情况很好。

有什么想法吗？ 我该如何解决？

Answer 1

在CPP项目（MathFuncsDll.h）中使用此示例代码行

extern "C" __declspec(dllexport) double Add(double a, double b);
extern "C" __declspec(dllexport) double Sub(double a, double b);
extern "C" __declspec(dllexport) double Mul(double a, double b);
extern "C" __declspec(dllexport) double Div(double a, double b);

在C＃代码中使用像这样

 [DllImport("MathFuncs.dll", CallingConvention = CallingConvention.Cdecl)]
 public static extern Double Add(Double a, Double b);

 [DllImport("MathFuncs.dll", CallingConvention = CallingConvention.Cdecl)]
 public static extern Double Mul(Double a, Double b);

 [DllImport("MathFuncs.dll", CallingConvention = CallingConvention.Cdecl)]
 public static extern Double Sub(Double a, Double b);

 [DllImport("MathFuncs.dll",CallingConvention = CallingConvention.Cdecl)]
 public static extern Double Div(Double a, Double b);

 [DllImport("MathFuncs.dll",CallingConvention = CallingConvention.Cdecl)]
 public static extern Double Bat(Double a, Double b);