#include <stdio.h>

typedef struct{
    int A;
    int B;
}*myStruct0;

typedef struct{
    int A;
    int C;
    int B;
}*myStruct1;

int AAr[3]={11,12,13};
int test(void * lp,int flag)
{
     if(flag==0)
            return ((myStruct0)lp)->B;
        
     return ((myStruct1)lp)->B;
}
int main()
{   
    myStruct0 AA;
    myStruct1 BB;
    
    printf("%d\n",test(AAr,1));
    printf("%d\n",test(AAr,0));

     return 0;
}
    

virtual at 0
myStruct0:
  .A dd ?
     .B dd ?
end virtual

virtual at 0
myStruct1:
        .A dd ?
     .C dd ?
     .B dd ?
end virtual
;
; DATA SECTION
;
AAr dd 11,12,13
;
; CODE SECTION
;
   mov     esi, AAr
    push    1
   pop     ecx
 call    test
        nop             ; <-- STOP IN DEBUGGER HERE AND SEE EAX

      dec     ecx
 call    test
        nop             ; <-- STOP IN DEBUGGER HERE AND SEE EAX
;
; FUNCTION test
;
test:
;
; ESI = lp
; ECX = flag
;
        jecxz   .esi_ptr_to_myStruct0

   mov     eax, [esi + myStruct1.B]
    ret

.esi_ptr_to_myStruct0:
       mov     eax, [esi + myStruct0.B]
    ret