get size of hidden struct C - c

Question

I'm trying to get the size of a struct that was defined in a different source file (other.c) to keep it hidden.
In the other.h:
typedef struct X x_t;
In the other.c:
struct X{
int y;
int z;
};
Now I want in the main.c to get the size of this struct.
#include "other.h"
int main(){
x_t *my_x;
my_x = malloc(sizeof(struct x_t));
return 0;}
But this gives me following error:
error: invalid application of ‘sizeof’ to incomplete type ‘struct x_t’
Can anybody help me? Thank you!

Answer 1

The whole purpose of having a hidden struct is to carefully control their construction, their destruction, and access to the contents.
Functions to construct, destruct, get the contents, and set the contents have to be provided to make the hidden struct useful.
Here's an example of what the .h and .c files could be:
other.h:
typedef struct X x_t;
x_t* construct_x(void);
void destruct_x(x_t* x);
void set_y(x_t* x, int y);
int get_y(x_t* x);
void set_z(x_t* x, int z);
int get_z(x_t* x);
other.c:
struct X {
int y;
int z;
};
x_t* construct_x(void)
{
return malloc(sizeof(x_t));
}
void destruct_x(x_t* x)
{
free(x);
}
void set_y(x_t* x, int y)
{
x->y = y;
}
int get_y(x_t* x)
{
return x->y;
}
void set_z(x_t* x, int z)
{
x->z = z;
}
int get_z(x_t* x)
{
rteurn x->z;
}