in piccolo progetto avevo bisogno di accedere a più di una struttura da più thread: ecco cosa mi sono inventato, grazie all’aiuto di stackoverflow e di un caro amico (full story in english: http://stackoverflow.com/questions/26005389/array-of-struct-and-sizeof/26024713#26024713)
ma passiamo subito al codice, come al solito autoesplicativo 
(seriamente, fate domande se avete bisogno)
#include <memory.h>
#include <stdio.h>
#include <stdlib.h>
/* BEGIN: just some struct to test, fell free to move them on external header file */
struct A
{
int a1;
long a2;
};
struct B
{
float b1;
char b2[6];
};
struct C
{
unsigned int c1;
double c2[5];
};
/* END: just some struct to test, fell free to move them on external header file */
/* this macro will create the right X macro element, and also initiliaze the "anonymous" struct */
#define ADD_STRUCT_TO_ARRAY(xu) X(xu, &(struct xu){})SEP
/* BEGIN: add or remove your own struct here!
* fell free to move them on external header file
* just need to pass struct name without "struct" to ADD_STRUCT_TO_ARRAY macro */
#define GENERIC_TABLE \
ADD_STRUCT_TO_ARRAY(A) \
ADD_STRUCT_TO_ARRAY(B) \
ADD_STRUCT_TO_ARRAY(C)
/* END: add or remove your own struct here! */
/* here we initialize the enum, where the type of the struct is the key, and its position in the array the value */
#define SEP ,
#define X(a,b) a
enum STRUCT {
GENERIC_TABLE
};
#undef X
/* here we initalize the array of pointer to the structure */
#define X(a,b) b
void * const generic[] =
{
GENERIC_TABLE
};
#undef X
#undef SEP
/* here we create all the getter function. add here your array locking code */
#define SEP ;
#define X(a,b) void get_##a(struct a * dest){memcpy(dest, generic[a], sizeof(struct a) );}
GENERIC_TABLE
#undef X
#undef SEP
/* here we create all the putter function. add here your array locking code */
#define SEP ;
#define X(a,b) void put_##a(struct a * source){memcpy(generic[a], source, sizeof(struct a) );}
GENERIC_TABLE
#undef X
#undef SEP
/*run, code, run!*/
int main()
{
struct A a_copy;
struct B b_copy;
struct C c_copy;
get_A(&a_copy);
get_B(&b_copy);
get_C(&c_copy);
printf("STRUCTURE IN ARRAY BEFORE INITIALIZATION\n");
printf("A = %d\n", a_copy.a1);
printf("B = %f\n", b_copy.b1);
printf("C = %x\n", c_copy.c1);
a_copy.a1 = -1;
b_copy.b1 = 2.3;
c_copy.c1 = 3;
printf("STRUCTURE CHANGED TO\n");
printf("A = %d\n", a_copy.a1);
printf("B = %f\n", b_copy.b1);
printf("C = %x\n", c_copy.c1);
printf("STRUCTURE SAVED\n");
put_A(&a_copy);
put_B(&b_copy);
put_C(&c_copy);
get_A(&a_copy);
get_B(&b_copy);
get_C(&c_copy);
printf("STRUCTURE LOADED\n");
printf("A = %d\n", a_copy.a1);
printf("B = %f\n", b_copy.b1);
printf("C = %x\n", c_copy.c1);
a_copy.a1 = 1000;
b_copy.b1 = -50.576;
c_copy.c1 = 700;
printf("STRUCTURE CHANGED TO\n");
printf("A = %d\n", a_copy.a1);
printf("B = %f\n", b_copy.b1);
printf("C = %x\n", c_copy.c1);
get_A(&a_copy);
get_B(&b_copy);
get_C(&c_copy);
printf("STRUCTURE RELOADED WITHOUT SAVING\n");
printf("A = %d\n", a_copy.a1);
printf("B = %f\n", b_copy.b1);
printf("C = %x\n", c_copy.c1);
return 0;
}
)