Hi,
I have a program that reads and writes files using ctypes. When I want it to
read AND write (e.g. read a file, select some stuff and write that), the
library returns a 'read-open' error. I think that the pointer to the file
handle for read and write point to the same address. To test that hypothesis, I
wrote the simplified code below. Problem is, that I can't make it work, let
alone come up with a solution. ;-( How do I tell ctypes to use a
particular chunck of memory, so read and write buffers do not mutually
interfere? Maybe the 'offset' parameter of ctypes.byref?
import ctypes
import platform
import os
import tempfile
# load libraries
pf = platform.platform().lower()
if pf.startswith("win"):
libc = ctypes.cdll.msvcrt
fopen = libc._fdopen
elif pf.startswith("lin"):
libc = ctypes.CDLL("libc.so.6")
fopen = libc.fdopen
elif pf.startswith("darwin"):
libc = ctypes.CDLL("libc.dylib")
fopen = libc.fdopen
else:
raise NotImplementedError
# create test data
path = tempfile.gettempdir()
os.chdir(path)
fn = "test.txt"
lines = 100 * (100 * "*" + os.linesep)
with open(fn, "wb") as f:
f.write(lines)
# read test data (code does NOT work)
fh = fopen(ctypes.c_char_p(fn), "rb")
fhPtr = ctypes.byref(ctypes.c_int(fh))
buff = ctypes.create_string_buffer(lines)
ret = libc.fread(buff, ctypes.c_int(1), ctypes.c_int(len(lines)), fhPtr)
print buff.value
# write test data (code does NOT work)
fn = "somefile.txt"
fh_out = fopen(ctypes.c_char_p(fn), "wb")
fh_outPtr = ctypes.byref(ctypes.c_int(fh_out))
buff = ctypes.create_string_buffer(lines)
ret = libc.fwrite(buff, ctypes.c_int(1), ctypes.c_int(len(lines)), fh_outPtr)
Thanks in advance!
Regards,
Albert-Jan
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
All right, but apart from the sanitation, the medicine, education, wine, public
order, irrigation, roads, a
fresh water system, and public health, what have the Romans ever done for us?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
_______________________________________________
Tutor maillist - Tutor@python.org
To unsubscribe or change subscription options:
http://mail.python.org/mailman/listinfo/tutor
