Re: storing related structs


"Gray Alien" <grey@xxxxxxxxxxxxx> ha scritto nel messaggio news:Z7OdnWRcAeZVoxvbnZ2dnUVZ8vidnZ2d@xxxxxxxxx
I have two related structs:


struct A
{
int x ;
void * data ;
};

and

struct B
{
int x, y ;
double z ;
void * data1, *data2 ;
};


These structures (not pointers to them), need to be stored in a another struct:

struct C
{
unsigned id ;
char name ;

DATA_TYPE the_struct ;
};


Where DATA_TYPE is EITHER a struct A or struct B.

For compatability with existing libraries, I cannot use a void * (for instance), and cast between struct A and B.


Is there a soln to this problem ?
struct C {
unsigned id;
char name; /* do you mean *name, or name[LARGE_ENOUGH]? */
enum { strA, strB } type;
union {
struct A str_A;
struct B str_B;
} the_struct;
};

A union is like a struct, but can only hold an element at a time.
You access members of unions like members of struct. For example,
in the case above to access the double of a struct B in a struct C,
you'll have to use mystructC.the_struct.str_B.z
Or try to find a better way to do what you're trying to do.


.

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