Ruby ffi::MemoryPointer equivalent in Python

[Sai Kiran]

Hi,

        I am trying to access C Code in Python,for that I am using Ctypes built-in in Python.

       A function in dll accepts 6 input parameters,Here is my Code.

       Here ,input is a huge array which consists of Complex numbers.

       buffer_size = c_int(len(input))

       real_array = (c_float * buffer_size.value)()

       for i in range(0,len(input)-1):

           real_array[i] = input[i].real

       imag_array = (c_float * buffer_size.value)()

       for i in range(0,len(input)-1):

           imag_array[i] = input[i].imag

       sign = c_int(-1)

       RealOutput = (c_float * buffer_size.value)()

       ImagOutput =  (c_float * buffer_size.value)()

       cfft( real_array ,imag_array,RealOutput,ImagOutput,sign.value, buffer_size.value)

       

       The Inputs passed were received by dll,in dll inputs are manipulated,real values,Imaginary values are stored in pointers RealOutput,ImagOutput respectively.

       while trying to print the data at RealOutput,ImagOutput 

Output:

       pOpReal[1] is -1.#QNAN0

       pOpImag[1] is -1.#QNAN0

       pOpReal[2] is -1.#QNAN0

       pOpImag[2] is -1.#QNAN0

       pOpReal[3] is -1.#QNAN0

       pOpImag[3] is -1.#QNAN0

       pOpReal[4] is -1.#QNAN0

       pOpImag[4] is -1.#QNAN0

       pOpReal[5] is -1.#QNAN0

       pOpImag[5] is -1.#QNAN0

In Ruby:

 

require 'ffi'

       pointers = Array.new( 4 ) { FFI::MemoryPointer.new( :float, size ) }

       * input is huge array of complex numbers

       Copying Input : 

        real_input = input.map { |c| c.to_c.real }

        imag_input = input.map { |c| c.to_c.imag }

        pointers[RealInput].write_array_of_float real_input

        pointers[ImagInput].write_array_of_float imag_input

     Copying Output:

        real_output = pointers[RealOutput].get_array_of_float( 0, buffer_size)

        imag_output = pointers[ImagOutput].get_array_of_float( 0, buffer_size)

Output :

      pOpReal[1] is -0.000063

      pOpImag[1] is -0.005755

      pOpReal[2] is -0.000076

      pOpImag[2] is 0.015815

      pOpReal[3] is 0.010016

      pOpImag[3] is -0.011680

      pOpReal[4] is -0.000109

      pOpImag[4] is -0.006708

      pOpReal[5] is -0.012282

      Successfully got the output.

Finally

1)Is there anything wrong in my approach

2)Is there any way to create MemoryPointers in Python like ruby.

     Thanks in advance.

[Armin Rigo]

Hi Sai,

On 1 May 2017 at 12:12, Sai Kiran <saipri...@gmail.com> wrote:
> I am trying to access C Code in Python,for that I am using Ctypes
> built-in in Python.

This is not the correct place to ask questions about ctypes: try e.g.
on stackoverflow.com.

This list is about cffi, which you may want to (but don't have to) use
instead of ctypes if you like. See the documentation at
http://cffi.readthedocs.io/ .


A bientôt,

Armin.