Question

Hallo!

I want a blob object which I can pass around in python and from time to time give it to a C++ function to write to.

ctypes seems the way to go but I have problem with the python standard functions.

For example:

>>> import ctypes
>>> T=ctypes.c_byte * 1000
>>> blob = T()
>>> ctypes.pointer(blob)
<__main__.LP_c_byte_Array_1000 object at 0x7f6558795200>

# Do stuff with blob data through the pointer in C++

>>> f = open('test.bin', 'wb')
>>> f.write(blob)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: argument 1 must be string or buffer, not _ctypes.ArrayType

I would really like to avoid copying the data if not necessary.

Thanks

Answer 1

You’ll probably have better luck with using string buffers and accessing the content through the raw attribute value

pstr = ctypes.create_string_buffer( 1000 )
f.write( pstr.raw )