无法封送“返回值":无效的托管/非托管类型组合 [英] Cannot marshal 'return value': Invalid managed/unmanaged type combination

问题描述

我在非托管库中有此功能，我想在C#中调用它:

I have this function in an unmanaged library and I want to call it in C#:

无符号字符__stdcall InitDev(无符号字符comport，长BaudRate)

这是在C#中

[System.Security.SuppressUnmanagedCodeSecurity]
[DllImport("*.dll", CallingConvention = CallingConvention.Cdecl,CharSet =CharSet.Auto)]
public static extern byte[] InitDev(byte[] comport, [Out]long BaudRate);

但是当我在C#中调用此函数时，出现以下错误

but when I call this function in C# I get the following error

无法封送'返回值':无效的托管/非托管类型组合."

"Cannot marshal 'return value': Invalid managed/unmanaged type combination."

string COM = "COM3";
byte[] ptr = new byte[1];
try
{
    ptr = InitDev(Encoding.ASCII.GetBytes(COM), 9600);
}
catch (Exception ex)
{
    MessageBox.Show(ex.Message);
}

如果您提供一些指导，我是陌生的，我将能够解决此问题

I am new to this if a little guidance is provided I will be able to resolve this issue

推荐答案

假定您的本地调用类似于 unsigned char * InitDef(unsigned char *，long long& baudRate)，那么您可能想要使用 IntPtr 代替 unsigned char * .但是首先，由于它是托管/非托管混合，因此应该为输入和输出分配该 byte [] 缓冲区:

Assuming your native call is something like unsigned char* InitDef(unsigned char*, long long &baudRate) then you probably want to use IntPtr in the place of your unsigned char*. But first since it's managed/unmanaged mixing you should allocate that byte[] buffer for input and output :

byte[] pInBuffer = Encoding.ASCII.GetBytes("COM3");
// allocate unmanaged memory
IntPtr inputBuffer = Marshal.AllocHGlobal(pInBuffer.Length * sizeof(byte));
Marshal.Copy(pInBuffer, 0, inputBuffer, pInBuffer.Length);

// now your inputBuffer contains a native pointer to the `unsigned char*`
// and since your function returns a new pointer to some `unsigned char*`
// just retrieve it to IntPtr
IntPtr result = InitDev(inputBuffer, 9600);

// free your allocated memory
Marshal.FreeHGlobal(inputBuffer);

在此阶段，您的结果包含从 InitDev 返回的值.

At this stage your result contains the value returned from InitDev.

InitDev 函数的新定义

new definition of InitDev function

[System.Security.SuppressUnmanagedCodeSecurity]
[DllImport("*.dll", CallingConvention = CallingConvention.Cdecl,CharSet =CharSet.Auto)]
public static extern IntPtr InitDev(IntPtr comport, [Out] long BaudRate);

所有必需的调用，都可以在

All of the necessary calls, you can find on this msdn page

由于您的本机呼叫看起来像这样: extern unsigned char __stdcall InitDev(unsigned char comport，long BaudRate);
我猜第一个参数只是您"COMn" 的最后一位数字(索引)，因为 unsigned char 的最低可能值为0，而COM的最低索引可以为 0.

EDIT :
Since your native call looks like this :extern unsigned char __stdcall InitDev(unsigned char comport,long BaudRate);
I'm guessing that the first parameter is just the last digit ( index ) of your "COMn" because unsigned char's lowest possible value is 0 and COM's lowest index can be 0.

尝试使用此代码段:

[System.Security.SuppressUnmanagedCodeSecurity]
[DllImport("*.dll", CallingConvention = CallingConvention.Cdecl,CharSet =CharSet.Auto)]
public static extern byte InitDev(byte comport, long BaudRate);

然后这样称呼它:

byte comIdx = 3;
byte result = InitDev(comIdx, 9600);
// byte should yield correct result now

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