Create SWIG C# wrapper for function that contains void* parameter

问题

I'm trying to create a C# wrapper for a C .lib that contains functions take take a void pointer using SWIG.

int inputPointExample(void* input);
int outputPointerExample(void* output);

By default SWIG doesn't handle void pointer conversions, you have to use typemaps somehow. I found this page -> http://www.nickdarnell.com/2011/05/swig-and-a-miss/ Number 9 says to use the following typemaps to handle void pointers...

%typemap(ctype)  void * "void *"
%typemap(imtype) void * "IntPtr"
%typemap(cstype) void * "IntPtr"
%typemap(csin)   void * "$csinput"
%typemap(in)     void * %{ $1 = $input; %}
%typemap(out)    void * %{ $result = $1; %}
%typemap(csout)  void * { return $imcall; }

When I try that I get a compile error in my exampleVectorType.cs in this function...

public IntPtr pData {
set {
  examplePINVOKE.ExampleVectorType_pData_set(swigCPtr, value);
} 
get {
  global::System.IntPtr cPtr = examplePINVOKE.ExampleVectorType_pData_get(swigCPtr);
  SWIGTYPE_p_void ret = (cPtr == global::System.IntPtr.Zero) ? null : new SWIGTYPE_p_void(cPtr, false);
  return ret; //Compile error occurs here
    } 
}

I got-

Cannot implicitly convert type 'SWIGTYPE_p_void' to 'System.IntPtr'

From what I was able to find, many others are having problems with this as well and there are only a few poor examples on how to fix this. Can someone help me out here?

回答1:

I've tried this with

// c++
void* GetRawPtr()
{
    return (void*)_data;
}

which swigs to

// swig generated c#
// Example.cs
IntPtr GetRawPtr()
{
    return examplePINVOKE.Example_GetRawPtr(swigCPtr);
} 

// examplePINVOKE.cs
[global::System.Runtime.InteropServices.DllImport("example", EntryPoint="CSharp_Example_GetRawPtr")]
public static extern IntPtr Example_GetRawPtr(global::System.Runtime.InteropServices.HandleRef jarg1);

if the following line is removed, then i get the code you had:

%typemap(csout)  void * { return $imcall; }

perhaps SWIG doesn't support typemapping well with properties? If you don't use get/set properties for your pData, it should work (as I've gotten it to work for me)

回答2:

I had a similar issue, but my case included struct fields:

struct foo {
   void* bar;
};

I was able to get Swig to work by using this:

%typemap(ctype)  void* "void *"
%typemap(imtype) void* "System.IntPtr"
%typemap(cstype) void* "System.IntPtr"
%typemap(csin)   void* "$csinput"
%typemap(in)     void* %{ $1 = $input; %}
%typemap(out)    void* %{ $result = $1; %}
%typemap(csout, excode=SWIGEXCODE)  void* { 
    System.IntPtr cPtr = $imcall;$excode
    return cPtr;
    }
%typemap(csvarout, excode=SWIGEXCODE2) void* %{ 
    get {
        System.IntPtr cPtr = $imcall;$excode 
        return cPtr; 
   } 
%}

I don't totally understand this stuff, but I believe the excode portion only matters if you're using exceptions. Overriding the property's get accessor via csvarout seems to be the key.

来源：https://stackoverflow.com/questions/25310530/create-swig-c-sharp-wrapper-for-function-that-contains-void-parameter

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