#define with member from structured pointer

Question

I have a structure like :

struct spidev_data {
  int busy;
  int irq;
};

And I just want to access a member ( like spidev->busy ) by a define, so I try this:

#define BUSY spidev->busy

But it does not work...

Can someone tell me how to do this ?

Thanks !

Always include the error message! And a small bit of code showing the error. The `#define` by itself will not give an error, you get the error when using it. — MSalters, Apr 23 '13 at 15:05
@stijn: you probably want an `inline` before that, and for C a `struct` before `spidev_data` — MSalters, Apr 23 '13 at 15:06
Yes spidev is a pointer to the structure ! Your answer is cool BLUEPIXY , but i prefer avoid using argument in my macro... — Raphaël Poggi, Apr 23 '13 at 15:07
@MSalters my macro doesn't work because she's raising a seg fault :/ and when i use directly spidev->busy, i don't have a seg fault. — Raphaël Poggi, Apr 23 '13 at 15:08
@RaphaëlPoggi: Then show us **both** snippets of code. Since the `#define` is a simple text replacement, I find your claim very hard to believe. — MSalters, Apr 23 '13 at 15:10
This post is a useless waste of time without a SSCCE (sscce.org) — Jim Balter, Apr 23 '13 at 15:23
@RaphaëlPoggi [Read my this answer](http://stackoverflow.com/questions/15167542/structure-pointer-operator-conjecture-theory/15167955#15167955) — Grijesh Chauhan, Apr 23 '13 at 15:37

masoud · Accepted Answer · 2013-04-23T15:27:36.833

3

You should try this

spidev_data *spidev = /* ... new or malloc ... */;

BUSY = 1;

But more elegant is

#define BUSY(X) (X)->busy

...

BUSY(spidev) = 1;

because it is not specially for an object.

edited Apr 23 '13 at 15:27

answered Apr 23 '13 at 15:06

masoud

1

I think that it should be `(X)->busy` – Alex Apr 23 '13 at 15:18
I'd recommend to add parentheses around the 2nd occurrence o `X` in the `#define`. – alk Apr 23 '13 at 15:23

1 Answers1