Python 中调用C DLL printf 输出顺序的问题研究

Python中有段代码

# -*- coding: utf-8 -*-
import ctypes
from ctypes import windll


def callc():
    """
    调用C动态库中的函数
    """
    somelibc = windll.LoadLibrary(r"C:\...\CDllForPython.dll")
    print ("Start")
    n = somelibc.fnC()
    print (n)
    print ("End")
    return n


if __name__ == '__main__':
    callc()

其中 CDllForPython.dll 中的fnC函数,如下

CDLL_API int   fnC()
{
    printf("temp");
    return sizeof(int) * 123;
}

在fuC中调用了printf.

在Python中调用fnC时,并没有按调用的先后顺序输出,实际输出顺序是

Start
492
End
temp

而期望的输出顺序是

Start
temp
492
End

在https://eli.thegreenplace.net/2015/redirecting-all-kinds-of-stdout-in-python/上有说明

The output order may not be what we expected. This is due to buffering. If it's important to preserve order between different kinds of output (i.e. between C and Python), further work is required to disable buffering on all relevant streams.

下一步的工作就是把相应的缓存禁用掉.