如何使用 boost.python 将预填充的"unsigned char*"缓冲区传递给C++方法？

可能值得考虑将Python辅助函数作为ExampleClass.printBuffer方法公开给Python，该方法委托给c-ish ExampleClass::printBuffer成员函数。例如，这将允许Python用户调用:

import example
import struct
buf = struct.pack('BBBB', 0x41, 0x42, 0x43, 0x44)
e.printBuffer(buf)

而不是要求用户执行正确的ctypes铸造和尺寸

struct.pack()方法在Python2中返回str对象，在Python3中返回bytes对象，因此辅助c++函数需要用str或bytes中的元素填充连续的内存块。boost::python::stl_input_iterator可以提供一种方便的方法，从Python对象(如str或bytes)构造c++容器(如std::vector<char>)。唯一奇怪的是stl_input_iterator期望Python类型支持iterable协议，而str不支持。但是，内置的iter() Python方法可用于创建可迭代对象。

/// @brief Auxiliary function used to allow a Python iterable object with char
///        elements to be passed to ExampleClass.printBuffer().
void example_class_print_buffer_wrap(
  ExampleClass& self,
  boost::python::object py_buffer)
{
  namespace python = boost::python;
  // `str` objects do not implement the iterator protcol (__iter__),
  // but do implement the sequence protocol (__getitem__).  Use the
  // `iter()` builtin to create an iterator for the buffer.
  // >>> __builtins__.iter(py_buffer)
  python::object locals(python::borrowed(PyEval_GetLocals()));
  python::object py_iter = locals["__builtins__"].attr("iter");
  python::stl_input_iterator<char> begin(
     py_iter(py_buffer)), end;
  // Copy the py_buffer into a local buffer with known continguous memory.
  std::vector<char> buffer(begin, end);
  // Cast and delegate to the printBuffer member function.
  self.printBuffer(
    reinterpret_cast<unsigned char*>(&buffer[0]),
    buffer.size());
}

BOOST_PYTHON_MODULE(example)
{
  namespace python = boost::python;
  python::class_<ExampleClass>("ExampleClass")
    .def("printBuffer", &example_class_print_buffer_wrap)
    ;
}

下面是演示这种方法的完整示例:

#include <cstdio>
#include <vector>
#include <boost/python.hpp>
#include <boost/python/stl_iterator.hpp>
// Mocks...
/// @brief Legacy class that cannot be changed.
class ExampleClass
{
public:
  void printBuffer(unsigned char* buffer, unsigned int length)
  {
    for (unsigned int i = 0; i < length; ++i)
    {
      printf("%c", buffer[i]);
    }
    printf("n");
  }
};
/// @brief Auxiliary function used to allow a Python iterable object with char
///        elements to be passed to ExampleClass.printBuffer().
void example_class_print_buffer_wrap(
  ExampleClass& self,
  boost::python::object py_buffer)
{
  namespace python = boost::python;
  // `str` objects do not implement the iterator protcol (__iter__),
  // but do implement the sequence protocol (__getitem__).  Use the
  // `iter()` builtin to create an iterator for the buffer.
  // >>> __builtins__.iter(py_buffer)
  python::object locals(python::borrowed(PyEval_GetLocals()));
  python::object py_iter = locals["__builtins__"].attr("iter");
  python::stl_input_iterator<char> begin(
     py_iter(py_buffer)), end;
  // Copy the py_buffer into a local buffer with known continguous memory.
  std::vector<char> buffer(begin, end);
  // Cast and delegate to the printBuffer member function.
  self.printBuffer(
    reinterpret_cast<unsigned char*>(&buffer[0]),
    buffer.size());
}
BOOST_PYTHON_MODULE(example)
{
  namespace python = boost::python;
  python::class_<ExampleClass>("ExampleClass")
    .def("printBuffer", &example_class_print_buffer_wrap)
    ;
}

>>> import example
>>> import struct
>>> buf = struct.pack('BBBB', 0x41, 0x42, 0x43, 0x44)
>>> print 'python:', buf
python: ABCD
>>> e = example.ExampleClass()
>>> e.printBuffer(buf)
ABCD

python文档在基本数据类型一章中列出了以下内容:

类ctypes。 c_char_p

指向以零结尾的字符串时，表示C char * 数据类型。用于一般字符指针也可以指向二进制数据，必须使用POINTER(c_char)。的构造函数接受整型地址或字符串。

显示您可能应该使用c_char_p类型。如果你使用POINTER()函数，这将是一个LP_c_char_p。

类型

LP_c_ubyte   /* corresponds to */  unsigned char;

LP_c_char_p    /* which corresponds to */    char *;

:我已经更正了上面的类型。另外:我不是python专家，所以我可能弄错了。