need help with a struct/memory

I need a struct that will contain a memory address, and a variable number mixed type variables.

typedef struct
{
LONG ExAddress;
LONG SizeVar;
????? Var????;
} EXDAT, *PEXDAT;

the var part will actually need to be a struct also

typedef struct
{
string typeName;
LONG/DOUBLE/??? typeMemValue;
} VARDSCR, *PVARDSCR;

my C++ is as always rusty; so I have completely forgotten how to work with dynamic arrays....

this struct is going to be used for cross process comunication by alloc space in target process and then writing the struct to it. The code that uses the struct will be thread injected imediable after the struct in mem allowing it to find it's location by the size of the struct...

I don't need help with the inection or anything at this point just can't remember how to do the array.. and I could use info on storing the actualy memory value in either some numeric type or an LPVOID or...?

Thanks for any help in advance.