PyBind11：绑定使用双指针的函数 [英] PyBind11: binding a function that uses double pointers

问题描述

我想将C ++函数与PyBind11绑定。问题在于此函数具有带双指针的参数，并且编译器引发错误

I would like to bind a C++-function with PyBind11. The problem is that this functions has an argument with a double pointer and the compiler raises an error

错误：无法初始化'char类型的参数右值类型为'typename make_caster< char **> ::: cast_op_type< typename std :: add_rvalue_reference< char **> :: type>'（又名'char *'）。

具体的代码如下：

#include <pybind11/pybind11.h>

#include <iostream>

namespace py = pybind11;

void parse_args(int argn__, char** argv__)
{
  for(int i = 1; i < argn__; ++i)
    {
      std::cout<< argv__[i];
    }
}

PYBIND11_MODULE(argv_bind, m) {
   m.def("parse_args", &parse_args);     
}

推荐答案

用于非简单参数类型（例如，像您的 char ** 一样），您必须包装函数本身，在此包装器中，逻辑提供了从较简单的类型或Python对象转换为所需的逻辑

For non-simple argument types (e.g. like your char **) you'll have to wrap the function itself, where your wrapper provides the logic to go from a simpler type or a Python object to the desired type.

在这种情况下， char * 实际上是一种非常不安全的类型，因为它不会无法清除内存；为了使此功能更强大，您需要使用 std :: string s，然后可以从其中访问 char * 通过 c_str（）方法。 （在pybind11中，即使您使用 char * 参数，这些实际上只是指向 std :: string 参数的指针： Python API故意不让调用者访问Python字符串的内部存储。）

In this case, char * are actually a pretty unsafe type to work with, since it doesn't get memory cleanup; to make this work robustly you'll need to take std::strings, from which you can then access the char * via the c_str() method. (In pybind11, even when you take char * arguments, those are really just pointers into std::string arguments: the Python API deliberately doesn't let callers access the internal storage of Python strings).

因此，您只想将其与类型本身可以将整个内容公开为 char ** ，这几乎是 std :: vector 的含义设计要做。这是一个适合您示例代码的包装器：

So then you just want to combine it with a type that can itself expose the whole thing as a char **, which is pretty much what std::vector is designed to do. Here's a wrapper that would fit your example code:

#include <pybind11/stl.h>

m.def("parse_args", [](std::vector<std::string> args) {
    std::vector<char *> cstrs;
    cstrs.reserve(args.size());
    for (auto &s : args) cstrs.push_back(const_cast<char *>(s.c_str()));
    return parse_args(cstrs.size(), cstrs.data());
});

（如果您的 parse_args 实际上需要 const char ** ，您可以删除 const_cast ）。

(If your parse_args actually takes a const char ** you can drop the const_cast).

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