good macro practice in c

Question

what is the better way to use macro and why 1)

CHECK(foo()); #define CHECK(foo) do{ \ UCHAR status = foo; \ if(0 != status) \ // do some stuff \ return status; \ }while(0)

or 2)

UCHAR status = foo(); CHECK(status); #define CHECK(status) do{ \ if(0 != status) \ // do some stuff \ return status; \ }while(0)

edited

thank You for all of You guys, a lot of people say that it is not good to use such piece of the code, but I have a lot of such pieces in my code (which I didn't write, only modify), what can You suggest?

To me, the first form is the more general and also (just imo) the more readable. — Pete Wilson
– Pete Wilson, Commented Sep 24, 2011 at 13:30
@geek 24 questions asked, 0 votes cast. That's pretty poor participation. Have a read of the faq. — David Heffernan
– David Heffernan, Commented Sep 24, 2011 at 13:37
@David Heffernan: Where does it say in the faq that you should be voting? (As a side note, it is a fundamental right in every decent democracy that you are not forced to vote, which is a good thing!) — bitmask
– bitmask, Commented Sep 24, 2011 at 13:43
@user786653, I would moderate that statement. Macros that do flow control should at least reflect that fact in their name. Something like ON_ERROR_RETURN or so. — Jens Gustedt
– Jens Gustedt, Commented Sep 24, 2011 at 14:15

Matteo Italia · Accepted Answer · 2011-09-24 13:30:37Z

1

I'd say the first one, since it takes care of avoiding multiple evaluation of foo, and who uses it doesn't need to remember to create the extra variable.

Still, personally I don't like macros that alter the execution flow like that, a programmer first seeing the codebase can easily miss a return point of the function.

answered Sep 24, 2011 at 13:30

Matteo Italia

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3 Comments

geek Over a year ago

but if I have a LOT such pieces of the code, what may be better than this?

Karoly Horvath Over a year ago

I think it's fine for a small DSL for reading a config file or running a state machine where code conciseness has higher importance and you can have the presupposition that whoever touches the code understands what those macros do.

Matteo Italia Over a year ago

Sure, I'm not saying that they must be avoided at all cost, I'm just saying that, as always, you have to consider the clarity/convenience tradeoff.

David Heffernan · Accepted Answer · 2011-09-24 13:30:06Z

Option 1 is easier to use since there is no need for the caller to worry about multiple evaluations of foo(). Option 1 also keeps the scope of the status variable as small as possible. Option 2 leaks the status variable into the scope of the caller.

Option 3 which doesn't use a macro at all is even better!

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