[英]How to pass a vector by reference in pybind11 & c++
I try to pass vector/array by reference from python through pybind11 to a C++ library.我尝试通过引用从 python 通过 pybind11 将向量/数组传递到 C++ 库。 The C++ library may fill in data. C++ 库可以填写数据。 After the call to C++, I hope the python side will get the data.调用C++后,希望python端能拿到数据。
Here is the simplified C++ code:这是简化的 C++ 代码:
#include <pybind11/pybind11.h>
#include <pybind11/numpy.h>
#include <pybind11/stl.h>
class Setup
{
public:
Setup(int version) : _version(version) {}
int _version;
};
class Calculator
{
public:
Calculator() {}
static void calc(const Setup& setup, std::vector<double>& results) { ... }
}
namespace py = pybind11;
PYBIND11_MODULE(one_calculator, m) {
// optional module docstring
m.doc() = "pybind11 one_calculator plugin";
py::class_<Setup>(m, "Setup")
.def(py::init<int>());
py::class_<Calculator>(m, "Calculator")
.def(py::init<>())
.def("calc", &Calculator::calc);
}
On the python side, I intend to:在 python 方面,我打算:
import os
import sys
import numpy as np
import pandas as pd
sys.path.append(os.path.realpath('...'))
from one_calculator import Setup, Calculator
a_setup = Setup(1)
a_calculator = Calculator()
results = []
a_calculator.calc(a_setup, results)
results
Apparently the results are not passed back.显然结果没有传回。 Is there a neat way to do it?有没有一种巧妙的方法来做到这一点?
Figured out a way:想出了一个办法:
#include <pybind11/pybind11.h>
#include <pybind11/numpy.h>
#include <pybind11/stl.h>
#include "Calculator.h" // where run_calculator is
namespace py = pybind11;
// wrap c++ function with Numpy array IO
int wrapper(const std::string& input_file, py::array_t<double>& in_results) {
if (in_results.ndim() != 2)
throw std::runtime_error("Results should be a 2-D Numpy array");
auto buf = in_results.request();
double* ptr = (double*)buf.ptr;
size_t N = in_results.shape()[0];
size_t M = in_results.shape()[1];
std::vector<std::vector<double> > results;
run_calculator(input_file, results);
size_t pos = 0;
for (size_t i = 0; i < results.size(); i++) {
const std::vector<double>& line_data = results[i];
for (size_t j = 0; j < line_data.size(); j++) {
ptr[pos] = line_data[j];
pos++;
}
}
}
PYBIND11_MODULE(calculator, m) {
// optional module docstring
m.doc() = "pybind11 calculator plugin";
m.def("run_calculator", &wrapper, "Run the calculator");
}
Python side Python侧
results= np.zeros((N, M))
run_calculator(input_file, results)
This way I also do not expose classes Setup and Calculator to the python side.这样,我也不会将类 Setup 和 Calculator 暴露给 python 端。
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