Using struct timeval in Python

Question

I have a C program containing a structure

struct S{
           int x;
           struct timeval t;
 };

and a function

int func(struct S s1, struct S s2)

I need to call this function from my python program. I am using ctypes.The parallel structure on Python

import ctypes
from ctypes import *
class S(Structure):
        _fields_ = [("x",c_int),
                     ("t", ?)]

Now, my question is what will I write in the ? place and any dependencies related to it. Thanks in advance.

My advice - it will work for a good number of platforms but not for all, make sure what is the OS Target and test. — Tiago Peczenyj, May 14 '13 at 17:53

score 6 · Accepted Answer · answered Apr 11 '12 at 14:30

6

Find the definition of struct timeval in your platform's C include files (the Internet suggests sys/time.h), then transcode that into a ctypes structure.

On my platform a struct timeval is

struct timeval {
  long tv_sec;
  long tv_usec;
};

(and I suppose this is the standard anyway), so

class timeval(Structure):
    _fields_ = [("tv_sec", c_long), ("tv_usec", c_long)]

class S(Structure):
    _fields_ = [("x",c_int), ("t", timeval)]

would probably fit the bill.

answered Apr 11 '12 at 14:30

AKX

152,115
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1

one more question.. does this structure(timeval) changes from platform to platform? – Sudip Apr 12 '12 at 06:29
4

YES it changes, NetBSD 6.0 (or superior) in 64 bits for example. Be careful. – Tiago Peczenyj May 14 '13 at 17:51
3

@tiago-peczenyj What is the smart way to deal with these platform dependencies? – hanno Sep 13 '16 at 18:58

score 2 · Answer 2 · answered Apr 11 '12 at 14:31

2

without any further info, it will be the definition of timeval:

class timeval(Structure):
    _fields_ = [("tv_sec",c_long),
                 ("tv_usec", c_long)]

class S(Structure):
    _fields_ = [("x",c_int),
                 ("t", timeval)]

answered Apr 11 '12 at 14:31

Lie Ryan

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Using struct timeval in Python

2 Answers2