c++ - Complicated test to check which object instantiates a function call -

i have struct ( can class ) , defined in class shown

struct a{ somedata_a; somespecificimplementation_a(someclass *s1); };  class someclass{ somedata_someclass; a; };  main(){  someclass c1, *c2;  c2 = &c1;  c1.a.somespecificimplementation_a(c2); } 

how verify c2 indeed reference c1? pardon me putting example obvious c2 reference c1.

update: not store pointer someclass

if don't know nothing parent, compare member' adresses

void a::somespecificimplementation_a(someclass *s1) {     if (this == &(s1->a)) {         // parent == s1     } else {         // parent != s1     } }