Python ctypes, working with struct typedefs

Question

Say I have the following c code:

typedef struct _test test;

struct _test {
    test*    just_a_test;
    char*    just_a_char;
};

Would the following implementation work?

class test(Structure):
    _fields_ = [
        ('just_a_test', POINTER(test)),
        ('just_a_char', c_char_p),
    ]

I'm just confused regarding the first pointer in the structure.

yak · Accepted Answer · 2012-01-20 06:15:10Z

3

Your code will not work because at the time it references test, the class hasn't been created yet.

This exact problem in described in ctypes documentation under 15.17.1.16. Incomplete Types.

The solution is to set _fields_ after creating the class:

class test(Structure):
    pass
test._fields_ = [
    ('just_a_test', POINTER(test)),
    ('just_a_char', c_char_p),
]

answered Jan 20, 2012 at 6:06

yak

9,1012 gold badges34 silver badges25 bronze badges

Sign up to request clarification or add additional context in comments.

1 Answer 1