如何公开原始字节的缓冲区与升压:: Python的？ [英] How to expose raw byte buffers with Boost::Python?

问题描述

我有第三方C ++库中，一些类方法使用原始字节的缓冲区。我不太确定如何处理在升压:: Python的吧。

I've got third party C++ library in which some class methods use raw byte buffers. I'm not quite sure how to deal in Boost::Python with it.

C ++库头是一样的东西：

C++ library header is something like:

class CSomeClass
{
  public:
      int load( unsigned char *& pInBufferData, int & iInBufferSize );
      int save( unsigned char *& pOutBufferData, int & iOutBufferSize );
}

在套牢了boost :: Python的code ...

In stuck with the Boost::Python code...

class_<CSomeClass>("CSomeClass", init<>())
    .def("load", &CSomeClass::load, (args(/* what do I put here??? */)))
    .def("save", &CSomeClass::save, (args(/* what do I put here??? */)))

我如何包装这些原始缓冲区它们暴露在Python原始字符串？

How do I wrap these raw buffers to expose them as raw strings in Python?

推荐答案

您已经写了，你自己，你的绑定功能，将返回<一个href=\"http://docs.python.org/2/c-api/buffer.html?highlight=buffer#buffers-and-memoryview-objects\">Py_buffer从数据对象，允许你要么只读（使用 PyBuffer_FromMemory ）或读写（使用 PyBuffer_FromReadWriteMemory ）您的pre-分配的C / C ++内存从Python的。

You have to write, yourself, functions on your bindings that will return a Py_buffer object from that data, allowing your to either read-only (use PyBuffer_FromMemory) or read-write (use PyBuffer_FromReadWriteMemory) your pre-allocated C/C++ memory from Python.

这是它是如何将看起来像（反馈最受欢迎）：

This is how it is going to look like (feedback most welcome):

#include <boost/python.hpp>

using namespace boost::python;

//I'm assuming your buffer data is allocated from CSomeClass::load()
//it should return the allocated size in the second argument
static object csomeclass_load(CSomeClass& self) {
  unsigned char* buffer;
  int size;
  self.load(buffer, size);

  //now you wrap that as buffer
  PyObject* py_buf = PyBuffer_FromReadWriteMemory(buffer, size);
  object retval = object(handle<>(py_buf));
  return retval;
}

static int csomeclass_save(CSomeClass& self, object buffer) {
  PyObject* py_buffer = buffer.ptr();
  if (!PyBuffer_Check(py_buffer)) {
    //raise TypeError using standard boost::python mechanisms
  }

  //you can also write checks here for length, verify the 
  //buffer is memory-contiguous, etc.
  unsigned char* cxx_buf = (unsigned char*)py_buffer.buf;
  int size = (int)py_buffer.len;
  return self.save(cxx_buf, size);
}

后来，当您绑定 CSomeClass ，请使用上面的替代方法负荷和<$静态功能C $ C>保存：

Later on, when you bind CSomeClass, use the static functions above instead of the methods load and save:

//I think that you should use boost::python::arg instead of boost::python::args
// -- it gives you better control on the documentation
class_<CSomeClass>("CSomeClass", init<>())
    .def("load", &csomeclass_load, (arg("self")), "doc for load - returns a buffer")
    .def("save", &csomeclass_save, (arg("self"), arg("buffer")), "doc for save - requires a buffer")
    ;

这看起来Python的足够给我。

This would look pythonic enough to me.

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