我有一个 C++ 类,它有一个成员函数,它接受一个 unsigned char* 缓冲区和一个 unsigned int 长度作为参数并对它们进行操作。我已经用 Boost::Python 包装了这个类,并希望将一个预填充的缓冲区从 Python 脚本传递给这个类。 Python 端缓冲区是使用 struct.pack 创建的。我不知道如何使参数类型匹配并不断收到 Boost.Python.ArgumentError。
include/Example.h
#ifndef EXAMPLECLASS_H_
#define EXAMPLECLASS_H_
#include <cstdio>
class ExampleClass
{
public:
ExampleClass() {}
virtual ~ExampleClass() {}
void printBuffer(unsigned char* buffer, unsigned int length)
{
for (unsigned int i = 0; i < length; ++i)
{
printf("%c", buffer[i]);
}
printf("\n");
}
};
#endif
src/example.cpp
#include "Example.h"
int main(int argc, char** argv)
{
unsigned char buf[4];
buf[0] = 0x41;
buf[1] = 0x42;
buf[2] = 0x43;
buf[3] = 0x44;
ExampleClass e;
e.printBuffer(buf, 4);
return 0;
}
src/Example_py.cpp
#include <boost/python.hpp>
#include "Example.h"
using namespace boost::python;
BOOST_PYTHON_MODULE(example_py)
{
class_<ExampleClass>("ExampleClass")
.def("printBuffer", &ExampleClass::printBuffer)
;
}
脚本/example.py
#!/usr/bin/env python
import example_py
import struct
import ctypes
buf = struct.pack('BBBB', 0x41, 0x42, 0x43, 0x44)
print 'python:'
print buf
e = example_py.ExampleClass()
print 'c++:'
print e.printBuffer(ctypes.cast(ctypes.c_char_p(buf), ctypes.POINTER(ctypes.c_ubyte)), len(buf))
CMakeLists.txt(不完整)
include_directories(
include
${Boost_INCLUDE_DIRS}
${PYTHON_INCLUDE_DIRS}
)
add_library(example_py
src/Example_py.cpp
)
target_link_libraries(example_py ${Boost_LIBRARIES} ${PYTHON_LIBRARIES})
set_target_properties(example_py PROPERTIES PREFIX "")
add_executable(example src/example.cpp)
target_link_libraries(example example_py)
输出
$ ./example
ABCD
$ ./scripts/example.py
python: ABCD
c++:
Traceback (most recent call last):
File "/home/dustingooding/example/scripts/example.py", line 13, in <module>
print 'c++:', e.printBuffer(ctypes.cast(ctypes.c_char_p(buf), ctypes.POINTER(ctypes.c_ubyte)), len(buf))
Boost.Python.ArgumentError: Python argument types in
ExampleClass.printBuffer(ExampleClass, LP_c_ubyte, int)
did not match C++ signature:
printBuffer(ExampleClass {lvalue}, unsigned char*, unsigned int)
我尝试了多种不同的方法(直接传递'buf',将'buf'作为ctypes.c_char_p传递,创建一个ctypes.ubyte数组并用'buf'的内容填充它并传递它),但似乎都不起作用。
我不明白为什么 'LP_c_ubyte' 和 'unsigned char*' 不匹配。
编辑
这是一个带有现成代码库的 Github 项目。随意使用它。我添加了@Tanner 的修复程序。 https://github.com/dustingooding/boost_python_ucharp_example
最佳答案
可能值得考虑将 Pythonic 辅助函数公开为 ExampleClass.printBuffer
Python 的方法,委托(delegate)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
类型转换和定型。
struct.pack()
方法返回 str
Python2 中的对象和 bytes
Python3 中的对象,因此辅助 C++ 函数需要使用 str
中的元素填充连续的内存块。或 bytes
. boost::python::stl_input_iterator
可以提供一种方便的方式来构造C++容器,例如std::vector<char>
,来自 Python 对象,例如 str
或 bytes
.唯一奇怪的是 stl_input_iterator
期望 Python 类型支持可迭代协议(protocol),即 str
不做。但是,内置 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());
}
创建辅助函数后,只需要将其公开为ExampleClass.printBuffer
即可。方法:
BOOST_PYTHON_MODULE(example)
{
namespace python = boost::python;
python::class_<ExampleClass>("ExampleClass")
.def("printBuffer", &example_class_print_buffer_wrap)
;
}
这是一个完整的例子demonstrating这种方法:
#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)
;
}
交互使用:
>>> import example
>>> import struct
>>> buf = struct.pack('BBBB', 0x41, 0x42, 0x43, 0x44)
>>> print 'python:', buf
python: ABCD
>>> e = example.ExampleClass()
>>> e.printBuffer(buf)
ABCD
关于python - 如何使用 boost.python 将预填充的 "unsigned char*"缓冲区传递给 C++ 方法?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/32634765/