Strange macro, valid?

[Exit]

In a header I was looking at, I saw this...

#define MMM_X(x)_Z(z)	(0x0C + (((x)-1)*3 + ((z)-1))*4)

... is that valid? I don't recall seeing a macro like that before.

(Name changed to protect the innocent!!!)

[Zaccheus]

That looks wrong to me. Where did you find it?

[Mitsukai]

looks fine for me

[Exit]

Where did you find it?

In a buildroot kernel header for a KS8695 chip.

[sunnypalsingh]

looks fine for me

Why does it appear fine to you
Preprocessing directive are of the form

# define identifier replacement-list new-line

which defines an object-like macro that causes each subsequent instance of the macro name.

or

# define identifier lparen identifier-listopt ) replacement-list new-line

which defines a function-like macro with parameters, similar syntactically to a function call.

[Mitsukai]

the macro is FINE

the information by the OP is NOT

#define _Z(z) (z)+
#define MMM_X(x)_Z(z)	(0x0C + (((x)-1)*3 + ((z)-1))*4)

int main()
{
   int z = 5;
   MMM_X(5);
}

note _Z could also be a type or function!

Your Comeau C/C++ test results are as follows:

Comeau C/C++ 4.3.9 (Mar 27 2007 17:24:47) for ONLINE_EVALUATION_BETA1
Copyright 1988-2007 Comeau Computing.  All rights reserved.
MODE:strict errors C++ noC++0x_extensions

"ComeauTest.c", line 8: warning: expression has no effect
     MMM_X(5);
     ^


In strict mode, without -tused, Compile succeeded (but remember, the Comeau online compiler does not link).
Compiled with C++0x extensions DISabled.

[Exit]

the information by the OP is NOT

What, pray tell, is wrong with the information in the OP? The macro appears in the header as is, (with a different name), and is the only macro in the header. All the other #defines are constant base addresses, register offsets and bit masks.

[Mitsukai]

this is not a compilable example so the information by OP is not enough

[Zaccheus]

the macro is FINE

It looks wrong to me.

Can you think of a sensible use which does not result in a 'redundant operation' warning ?

[Mitsukai]

redundant operation?

just put int x = infront of the macro call

or make _Z a function or type

[Zaccheus]

redundant operation?

just put int x = infront of the macro call

Good point.


Nevertheless, the macro still looks wrong to me.