[ctypes] convert pointer to string?

[Neal Becker]

In an earlier post, I was interested in passing a pointer to a structure to
fcntl.ioctl.

This works:

c = create_string_buffer (...)
args = struct.pack("iP", len(c), cast (pointer (c), c_void_p).value)
err = fcntl.ioctl(eos_fd, request, args)

Now to do the same with ctypes, I have one problem.

class eos_dl_args_t (Structure):
    _fields_ = [("length", c_ulong),
                ("data", c_void_p)]
...
args = eos_dl_args_t()
args_p = cast(pointer(args), c_void_ptr).value
fcntl.ioctl(fd, request, args_p)  <<< May fail here

That last may fail, because .value creates a long int, and ioctl needs a
string.

How can I convert my ctypes structure to a string?  It _cannot_ be a c-style
0-terminate string, because the structure may contain '0' values.