具有ctypes的stdout重定向 [英] stdout redirection with ctypes
问题描述
我正在尝试将printf函数的输出重定向到Windows上的文件。我在python3上使用ctypes来调用函数。我的代码是:
I'm trying to redirect the output of printf functions to a file on Windows. I'm using ctypes with python3 to invoke the functions. My code is:
import os, sys
from ctypes import *
if __name__ == '__main__':
print("begin")
saved_stdout=os.dup(1)
test_file=open("TEST.TXT", "w")
os.dup2(test_file.fileno(), 1)
test_file.close()
print("python print")
cdll.msvcrt.printf(b"Printf function 1\n")
cdll.msvcrt.printf(b"Printf function 2\n")
cdll.msvcrt.printf(b"Printf function 3\n")
os.dup2(saved_stdout, 1)
print("end")
但是当我从Eclipse运行代码,我在屏幕上看到以下内容:
But when I run the code from Eclipse I get the following on the screen:
begin
end
Printf function 1
Printf function 2
Printf function 3
...以及TEST.txt中的以下内容
...and the following in the TEST.txt
python print
当我从cmd运行此命令时,这是屏幕上显示的内容:
When I run this from cmd, this is what is on the screen:
begin
end
..,这在TEST.txt中:
..and this is in the TEST.txt:
python print
当我注释掉第二个 dup2()时
语句,例如
When I comment out the second dup2()
statement e.g.
import os, sys
from ctypes import *
if __name__ == '__main__':
print("begin")
saved_stdout=os.dup(1)
test_file=open("TEST.TXT", "w")
os.dup2(test_file.fileno(), 1)
test_file.close()
print("python print")
cdll.msvcrt.printf(b"Printf function 1\n")
cdll.msvcrt.printf(b"Printf function 2\n")
cdll.msvcrt.printf(b"Printf function 3\n")
#os.dup2(saved_stdout, 1)
print("end")
从Eclipse在屏幕上:
From Eclipse, on the screen:
begin
...并在TEST.txt文件中:
...and in the TEST.txt file:
python print
end
Printf function 1
Printf function 2
Printf function 3
在屏幕上的cmd中:
begin
...并在TEST.txt文件中:
...and in the TEST.txt file:
python print
end
I'我现在完全感到困惑。我在StackOverflow上阅读了所有重定向线程,但不知道发生了什么。
无论如何,我收集到的是C函数访问直接绑定到文件描述符的stdout,而python为此使用了一个特殊对象-stdout File Object。因此,基本 sys.stdout = * something *
不适用于ctypes。
我什至在dup2输出上尝试过 os.fdopen(1)
,然后调用 flush()$ c在每个
printf
语句之后的$ c>,但是此操作不再起作用。
我现在完全没主意了,如果有人对此有解决方案,将不胜感激。
I'm totally confused now. I read all the redirection threads here on StackOverflow and I can't understand what's going on.
Anyway, what I've gathered is that C functions access the stdout that is bind directly to the file descriptor, while python uses a special object for that - stdout File Object. So the elementary sys.stdout=*something*
doesn't work with ctypes.
I've even tried os.fdopen(1)
on the dup2-ed output and then calling flush()
after every printf
statement but this isn't working again.
I'm totally out of ideas now and would appreciate if someone have a solution for this.
推荐答案
使用与CPython 3.x使用的相同的C运行时(例如,3.3的msvcr100.dll)。在重定向 stdout
之前和之后,还应包括对 fflush(NULL)
的调用。如果程序直接使用Windows API,请采取措施重定向Windows StandardOutput
句柄。
Use the same C runtime that CPython 3.x uses (e.g. msvcr100.dll for 3.3). Also include a call to fflush(NULL)
before and after redirecting stdout
. For good measure, redirect the Windows StandardOutput
handle, in case a program uses the Windows API directly.
如果DLL使用不同的C运行库(具有自己的POSIX文件描述符集),则此操作可能会变得复杂。也就是说,如果在重定向Windows StandardOutput
之后加载它,应该没问题。
This can get complicated if the DLL uses a different C runtime, which has its own set of POSIX file descriptors. That said, it should be OK if it gets loaded after you've redirected Windows StandardOutput
.
编辑:
我修改了示例,使其可以在Python 3.5+中运行。 VC ++ 14的新通用CRT使通过ctypes使用C标准I / O变得更加困难。
I've modified the example to run in Python 3.5+. VC++ 14's new "Universal CRT" makes it much more difficult to use C standard I/O via ctypes.
import os
import sys
import ctypes, ctypes.util
kernel32 = ctypes.WinDLL('kernel32')
STD_OUTPUT_HANDLE = -11
if sys.version_info < (3, 5):
libc = ctypes.CDLL(ctypes.util.find_library('c'))
else:
if hasattr(sys, 'gettotalrefcount'): # debug build
libc = ctypes.CDLL('ucrtbased')
else:
libc = ctypes.CDLL('api-ms-win-crt-stdio-l1-1-0')
# VC 14.0 doesn't implement printf dynamically, just
# __stdio_common_vfprintf. This take a va_array arglist,
# which I won't implement, so I escape format specificiers.
class _FILE(ctypes.Structure):
"""opaque C FILE type"""
libc.__acrt_iob_func.restype = ctypes.POINTER(_FILE)
def _vprintf(format, arglist_ignored):
options = ctypes.c_longlong(0) # no legacy behavior
stdout = libc.__acrt_iob_func(1)
format = format.replace(b'%%', b'\0')
format = format.replace(b'%', b'%%')
format = format.replace(b'\0', b'%%')
arglist = locale = None
return libc.__stdio_common_vfprintf(
options, stdout, format, locale, arglist)
def _printf(format, *args):
return _vprintf(format, args)
libc.vprintf = _vprintf
libc.printf = _printf
def do_print(label):
print("%s: python print" % label)
s = ("%s: libc _write\n" % label).encode('ascii')
libc._write(1, s, len(s))
s = ("%s: libc printf\n" % label).encode('ascii')
libc.printf(s)
libc.fflush(None) # flush all C streams
if __name__ == '__main__':
# save POSIX stdout and Windows StandardOutput
fd_stdout = os.dup(1)
hStandardOutput = kernel32.GetStdHandle(STD_OUTPUT_HANDLE)
do_print("begin")
# redirect POSIX and Windows
with open("TEST.TXT", "w") as test:
os.dup2(test.fileno(), 1)
kernel32.SetStdHandle(STD_OUTPUT_HANDLE, libc._get_osfhandle(1))
do_print("redirected")
# restore POSIX and Windows
os.dup2(fd_stdout, 1)
kernel32.SetStdHandle(STD_OUTPUT_HANDLE, hStandardOutput)
do_print("end")
这篇关于具有ctypes的stdout重定向的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!