使用 ctypes 从共享库映射全局变量

Question

I'd like to map an int value pbs_errno declared as a global in the library libtorque.so using ctypes.

Currently I can load the library like so:

from ctypes import *
libtorque = CDLL("libtorque.so")

and have successfully mapped a bunch of the functions. However, for error checking purposes many of them set the pbs_errno variable so I need access to that as well. However if I try to access it I get:

>>> pytorque.libtorque.pbs_errno
<_FuncPtr object at 0x9fc690>

Of course, it's not a function pointer and attempting to call it results in a seg fault.

It's declared as int pbs_errno; in the main header and extern int pbs_errno; in the API header files.

Objdump shows the symbol as:

00000000001294f8 g    DO .bss   0000000000000004  Base        pbs_errno

Answer 1

There's a section in the ctypes docs about accessing values exported in dlls:

http://docs.python.org/library/ctypes.html#accessing-values-exported-from-dlls

eg

def pbs_errno():
    return c_int.in_dll(libtorque, "pbs_errno")