I have been working on extending a Python application using ctypes to call a shared library in C code.
I have a boolean variable in Python which I would like to check periodically in an infinite loop in the C code to see if it changes. Is there a way to send the memory address of the Python variable to the C function and access the content?
You can't pass a reference to an actual Python bool. But you could make a ctypes.c_bool, pass a pointer to it to your C code, and then have Python code assign its .value attribute to change the value from C's point of view.
from ctypes import *
# Flag initially false by default, can pass True to change initial value
cflag = c_bool()
# Call your C level function, passing a pointer to c_bool's internal storage
some_c_func(byref(cflag))
# ... other stuff ...
# If C code dereferences the bool* it received, will now see it as true
cflag.value = True
volatile bool* (perhaps some sort of atomic), the optimizer could easily be caching the value from memory to a register once and never rereading the memory (I'm assuming threads are involved here, since otherwise the infinite loop in C would never return to Python, so Python would never get a chance to change the bool).