Swig typemap java对象 [英] Swig typemap java object

问题描述

我试图通过swig为这两个c ++函数生成java绑定

I am trying to generate java bindings through swig for these two c++ functions

C ++函数

void SetUserData(void* data);
void* GetUserData() const;

在java方面，我希望它看起来像这样

On the java side I want it to look like this

setUserData(Object object);
getUserData() //return java.lang.Object

我想要无效*指向我传递给它的任何java对象的指针。在我的swig文件中，我尝试添加这些行

I would like the void* pointer to point to any java object I pass to it. In my swig file I tried to add these lines

//swig file
%typemap(jstype) void* "java.lang.Object";
%apply Object {void*};

我收到编译错误：
b2Fixture.swig（22）：警告453：可以不适用（对象）。没有定义任何类型图。我不知道如何为此制作打字机。有什么想法？

I get a compile error: b2Fixture.swig(22) : Warning 453: Can't apply (Object). No typemaps are defined. I have no idea how to make typemaps for this. Any ideas?

推荐答案

您可能想这样做：

%apply jobject { void* };

因为％apply将在一个C ++类型上定义的类型映射复制到另一个C ++类型。 Object 是Java类型，而不是C ++类型，因此没有要复制的任何类型地图。另一方面， jobject 是等效的JNI。

because %apply copies the typemaps defined on one C++ type to another C++ type. Object is a Java type, not a C++ one so doesn't have any typemaps to be copied. jobject on the other hand is the JNI equivalent.

另外假设你想要'正常'的GC语义（即不需要保留您传递的任何数据）您需要做更多的工作，例如：

Additionally assuming you want to have 'normal' GC semantics (i.e. not be required to retain whatever data you pass in) you'll need to do some more work, for example:

%module test

%{
#include "test.hh"
%}

%apply jobject { void * };

%typemap(in) void * {
  void *old = getData();
  if (old) JCALL1(DeleteGlobalRef, jenv, (jobject)old);
  $1 = JCALL1(NewGlobalRef, jenv, $input);
}

%typemap(out) void * {
  $result = (jobject)($1);
}

%include "test.hh"

这为您的数据创建一个新的全局参考，这可能是唯一阻止它被GC释放的东西。

This makes a new Global Reference for your data, which could be the only thing keeping it from getting freed by the GC.

给定一个头文件：

void setData(void *);
void *getData();

和实施：

#include "test.hh"

namespace {
  void *d = nullptr;
}

void setData(void *d) {
  ::d = d;
}

void *getData() {
  return d;
}

这足以允许：

public class run {
  public static void main(String[] argv) {
    System.loadLibrary("test");
    Object example = "HELLO";
    test.setData(example);
    System.out.println(test.getData());
  }
}

正常工作。

如上所述，这些类型地图非常难看 - 它们会影响所有 c> void * 的使用。因此，如果你真的使用了这个，你会想要第二次使用％apply 或％clear 来限制它们的影响。您还可以在头文件中命名参数，并使用它来限制应用typemap的位置。

As written these typemaps are pretty ugly - they'll impact all usage of void *. So if you really used this you would want to use %apply or %clear a second time to limit their impact. You could also name the arguments in the header file and use that to limit where the typemap gets applied.

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