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  1.  
  2. from cffi import FFI
  3. import numpy as np
  5. s = '''
  6. typedef struct
  7. {
  8. int a;
  9. int b;
  10. float c;
  11. double d;
  12. } mystruct;
  13. '''
  14. ffi = FFI()
  15. ffi.cdef(s)
  17. m_arr = ffi.new("mystruct[2]")
  19. #create array and fill with dummy data
  20. for k in range(2):
  22. m = m_arr[k]
  24. m.a = k
  25. m.b = k + 1
  26. m.c = k + 2.0
  27. m.d = k + 3.0
  29. print(m_arr)
  31. # dtype for structured array in Numpy
  32. dt = np.dtype({'names': ('a', 'b', 'c', 'd'),
  33. 'formats': ('i4', 'i4', 'f4', 'f8'),
  34. 'offset': (ffi.offsetof('mystruct', 'a'),
  35. ffi.offsetof('mystruct', 'b'),
  36. ffi.offsetof('mystruct', 'c'),
  37. ffi.offsetof('mystruct', 'd'),
  38. )
  39. })
  40. padding = ffi.sizeof('mystruct') - dt.itemsize
  41. if padding:
  42. # this padding takes into account aligning arrays of structs
  43. dt = np.dtype({'names': ('a', 'b', 'c', 'd','padding'),
  44. 'formats': ('i4', 'i4', 'f4', 'f8', 'S%d' % padding),
  45. 'offset': (ffi.offsetof('mystruct', 'a'),
  46. ffi.offsetof('mystruct', 'b'),
  47. ffi.offsetof('mystruct', 'c'),
  48. ffi.offsetof('mystruct', 'd'),
  49. )
  50. })
  53. # member size, 20 bytes
  54. print('size, manually', 4 + 4 + 4 + 8)
  56. # total size of struct, 24 bytes
  57. print('sizeof', ffi.sizeof(m_arr[0]))
  60. #reason is member padding in structs
  62. buf = ffi.buffer(m_arr)
  63. print(buf)
  65. x = np.frombuffer(buf, dtype=dt)
  66. print(x)
  67.  
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