在C#中将结构指针作为参数传递 [英] Passing a struct pointer as a parameter in C#

问题描述

我在C ++中有一个导出到DLL的函数.我包含一个结构指针作为参数之一.我需要在C#中使用此函数，因此我将DLLImport用于该函数，并使用StructLayout在C#中重新创建了结构.我尝试使用ref传递参数，并尝试使用MarshalAs(UnmangedType.Struct)和Marshal.PtrToStructure封送它.参数仍然没有正确传递.

I have a function in C++ that I exported to a DLL. I contains a struct pointer as one of the parameters. I need to use this function in C#, so I used DLLImport for the function and recreated the struct in C# using StructLayout. I've tried passing in the parameter using ref as well as tried Marshaling it in using MarshalAs(UnmangedType.Struct) and Marshal.PtrToStructure. The parameter still isn't passing correctly.

示例:

[DllImport("testdll.dll")]
public static extern int getProduct(int num1, int num2, [MarshalAs(UnmanagedType.Struct)] ref test_packet tester);

信息的另一个花哨之处是，该结构包含一个byte * var，我认为这可能会导致将参数作为ref传递的问题.有任何想法吗?我在正确的轨道上吗?感谢您的帮助.

One more tidbit of info, the struct contains a byte* var, which I think may be causing the problem in terms of passing the param as ref. Any ideas? Am I on the right track? Thanks for the help.

感谢nobugz的响应.这是struct def的示例:

Thanks nobugz for the response. Here's a sample of the struct def:

//C# DEFINITION 

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)] 

public struct test_packet 
{ 

     public UInt32 var_alloc_size; 

    public byte* var; 

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = MAX_TAG_LENGTH)] 
    public byte[] tag; 

} 

//ORIGINAL UNMANAGED STRUCT

typedef struct test_packet_tag 
{

    unsigned int var_alloc_size;

    unsigned char *var;

    unsigned char tag[MAX_TAG_LENGTH];
} test_packet;

推荐答案

使用"ref"是正确的方法，摆脱[MarshalAs]属性.真正的问题几乎可以肯定是结构声明.您没有发布任何有助于我们帮助您的内容.

Using "ref" is the correct way, get rid of the [MarshalAs] attribute. The real problem is almost certainly the structure declaration. You didn't post anything that would help us help you with that.

DllImportAttribute.CharSet属性错误，将其设置为CharSet.Ansi.将"var"成员声明为错误，将其设置为byte [].请确保在调用之前对其进行初始化:

The DllImportAttribute.CharSet property is wrong, make it CharSet.Ansi. The "var" member is declared wrong, make it byte[]. Be sure to initialize it before the call:

 var product = new test_packet();
 product.var_alloc_size = 666;    // Adjust as needed
 product.var = new byte[product.var_alloc_size];
 int retval = getProduct(42, 43, ref product);

最好的猜测，希望它能起作用.

Best guess, hope it works.

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