void pointer to struct, element access using macros

Question

Given the following struct,

typedef struct tCard {
    CardClass class;
    void *proto;
} Card;

typedef struct tCardPath {
    PathType path_type;
    struct tPath path;
    Goal goal;
} CardPath;

Is it possible to access the element pointed by a pointer to struct (proto) using macros, like this?

((CardPath*)(trial[i].proto))->element1; // this works
CARD_PROP(trial[i], Path, element1); // the goal

I tried this, but this gives error: expected identifier before ‘(’ token when compiling,

#define PROTO(C) (C).proto
#define CARD_PROP(C, CARD, PROP) (((Card##CARD *)(PROTO(C)))->(PROP))

EDIT: Tried this, still doesn't work

#define CARD_PROP(C, CARD, PROP) ((Card##CARD *)(PROTO(C))->PROP

Your new edited macro produces exactly ((CardPath *)((trial[i]).proto)->element1;. Notice the 4 ( and the 3 ) — nos
– nos, Commented Nov 14, 2013 at 12:11
May I ask why do this? Smells like an XY problem. meta.stackexchange.com/a/66378 — user694733
– user694733, Commented Nov 14, 2013 at 13:36

Shahbaz · Accepted Answer · 2013-11-14 11:01:53Z

3

The problem is that you can't put members of a struct in parentheses. Your macro expands to:

((CardPath*)(trial[i].proto))->(element1)
                               ^^^^^^^^^^

Which shouldn't have parentheses where I marked above.

answered Nov 14, 2013 at 11:01

Shahbaz

47.8k19 gold badges120 silver badges187 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

void pointer to struct, element access using macros

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related