Thanks for the response! Is there, then, a standard way of calling a C function, creating an object (struct) that can hold two arrays, and then return that data object to the python program?


Nicholas Earl
Graduate Research Assistant
San Diego State University

On Sun, Sep 29, 2013 at 10:11 PM, Thor Andreas Tangen <> wrote:

The vectors times and fluxes are destroyed when exiting the function start, the memory allocated and pointed to be times and fluxes are invalid upon exiting the function.

Thor Andreas

On Sun, Sep 29, 2013 at 12:53 AM, Nicholas Earl <> wrote:
I'm struggling with returning a struct value using ctypes. Mainly, it keeps segfaulting when I try and get the values from the returned object. I have my python script setup like this:

import ctypes
import numpy as np
from numpy.ctypeslib import ndpointer

class PhotoInfo(ctypes.Structure):
    _fields_ = [
        ('times', ctypes.POINTER(ctypes.c_double)),
        ('fluxes', ctypes.POINTER(ctypes.c_double)),

def main():
    lib = ctypes.cdll.LoadLibrary('')

    start = lib.start
    start.restype = ctypes.POINTER(PhotoInfo)
    start.argtypes = [

    N = 3
    mass = np.array([0.00020335520, 5.977884E-05, 9.320397E-08])

    phin = start(N, mass)

    print phin[0].times[0]

And in my c file:

#include <iostream>
#include <iomanip>
#include <fstream>
#include <sstream>
#include <string>
#include <vector>
#include <math.h>
#include <stdlib.h>
#include <stdio.h>

using namespace std;

typedef struct {
  double *times;
  double *fluxes;
} PhotoInfo;

extern "C" {
  PhotoInfo *start(int N, double *mass);

PhotoInfo *start(int N, double *mass) {
  PhotoInfo phin;
  vector<double> times;
  vector<double> fluxes;

// Here, I read in a file and fill times and fluxes with doubles using
// times.push_back(t) and fluxes.push_back(f)\

  phin.times = &times[0];
  phin.fluxes = &times[0];
  return &phin;

Any guidance on this would be greatly appreciated!

Nicholas Earl
Graduate Research Assistant
San Diego State University

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