How to access C struct fields

[qinwf]

I asked ChatGPT, and here is the answer. Is this the best way to do it? If my struct has many fields, it might be a bit verbose to create separate getter and setter methods for each one.

If your C API uses pointers, you’ll get back and pass around opaque cobj handles in Codon. For example:

// mylib2.h
typedef struct { int a, b; } Pair;

// allocate on the heap
Pair* new_pair(int a, int b);

// read fields by value
int get_a(Pair* p);

You’d import as:

LIB = "libmylib2.so"
from C import LIB.new_pair(int, int) -> cobj as new_pair
from C import LIB.get_a(cobj)     -> int   as get_a

p = new_pair(3, 4)         # p is a cobj pointing to a Pair
print(get_a(p))            # reads the 'a' field

[arshajii]

You can usually just replicate the structure definition in Codon:

@tuple
class Pair:
    a: i32
    b: i32

Then you can use Ptr[Pair]:

LIB = "libmylib2.so"
from C import LIB.new_pair(i32, i32) -> Ptr[Pair] as new_pair  # note that C `int` == Codon `i32`

p = new_pair(i32(3), i32(4))
print(p[0].a)  # reads the 'a' field -- use int(..) to convert i32 to standard int