c - Having to know the structure offset in which a function pointer is declared -

is there way can call function (somewhere initialized) that:

mystruct.foo(); 

allowing foo() access mystruct structure inside.

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my goal use bit of object oriented programming in c , allow foo access members, part of mystruct structure.

there no way make happen magically, thing can think of this

#include <stdio.h>  #define declare_class_method(class, name, ...) \     (*name)(class *this, __va_args__)  typedef struct class class; struct class {     int declare_class_method(class, method, int value); };  int method(class *this, int value) {     fprintf(stderr, "%p: %d\n", (void *) this, value);     return 0; }  int main(void) {     class instance;      instance.method = method;     instance.method(&instance, 9);      return 0; } 

but can see must pass instance method, not happen automatically in oo language c++.