Problems of exposing const char * field in struct #2337
Description
Hi,
I found binding a struct contains const char * field may cause problems in my project. When I get a struct object from a function, the const char * field will be empty.
Here I use a prototype to show three situations:
// struct contains const char * field and other field.
struct A {
const char *a1;
int a2;
};
typedef struct A A;
A initA(const char *a1, int a2) {
return A{a1, a2};
}
// struct contains const char * field and a nested struct.
struct B {
const char * b;
A a;
};
typedef struct B B;
B initB(const char *b, A a) {
return B{b, a};
}
// struct only contains const char * field.
struct C {
const char *c;
};
typedef struct C C;
C initC(const char *c) {
return C{c};
}
And I use the following code to expose the fields in the struct:
PYBIND11_MODULE(test, m) {
py::class_<A>(m, "A")
.def_readwrite("a1", &A::a1)
.def_readwrite("a2", &A::a2);
m.def("initA", &initA);
py::class_<B>(m, "B")
.def_readwrite("b", &B::b)
.def_readwrite("a", &B::a);
m.def("initB", &initB);
py::class_<C>(m, "C")
.def_readwrite("c", &C::c);
m.def("initC", &initC);
}
The results:
>>> import test
>>> test_a = test.initA("test_a", 10)
>>> test_b = test.initB("test_b", test_a)
>>> test_c = test.initC("test_c")
>>> print(test_a.a1)
>>> print(test_b.b)
>>> print(test_c.c)
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xf0 in position 0: invalid continuation byte
The expected output should be:
>>> print(test_a.a1)
test_a
>>> print(test_b.b)
test_b
>>> print(test_c.c)
test_c
But the actual output is empty and UnicodeDecodeError. I tried def_readonly and def_readwrite to expose the const char * field, but they cause the same problem. I'm not sure is this because the lifetime of const char * has already ended when I want to print it? And why the string caused the UnicodeDecodeError? Am I missing something important, how could I solve these problems without touching the source code?
Thanks!