Passing a semicolon or comma as a Macro argument

[MattyWix]

Hi,

How can I pass a semicolon or a comma as a macro argument.
I wish to build an expression that in some cases has a comma - eg
building a list of members for a structure, but in other instances has
a comma - eg building a list of arguments for a function.

MattyWix

 

[Chris Dollin]

How can I pass a semicolon or a comma as a macro argument.

I don't think you can. (I don't think you can switch off the
argument-separating function of the comma.) There might be
deferred-macro-expansion tricks you can pull. Someone else
can propose those: I get twitchy with clever macro tricks.

I wish to build an expression that in some cases has a comma - eg
building a list of members for a structure, but in other instances has
a comma - eg building a list of arguments for a function.

Well, I have three\\\\\four suggestions (likely there are more
possibilities):

(a) Have two macros. Share common text as other macros.

(b) Use a non-C macro preprocessor.

(c) Generate the code, don't macro-process it.

(d) Back off and review the problem and see if there's a
completely different way of solving it.

Looking at the code you've shown us, I'd go for (d).

 

[Walter Banks]

#define comma ,
pass comma where you need a comma

 

[Christopher Benson-Manica]

Can you make any compilable example?

Sure:

#define comma ,
#define invoke(f,args) f(args)

#include <stdio.h>

int main(void)
{
invoke( printf, "Hello, world! %d, %d, %d\n" comma 1 comma 2 comma 3 );
return 0;
}

It should be obvious, however, that this is obfuscatory and thus a Bad
Idea. OP would be advised to find a different solution.

 

[Konstantin Miller]

#define comma ,
pass comma where you need a comma

Can you make any compilable example?

Konstantin

 

[Thad Smith]

(a) Have two macros. Share common text as other macros.

I like that approach:

#define LIST ITEM(a),ITEM(b),ITEM(c)

#define ITEM(x) x,
enum e {
LIST,
NUM_ENTRIES
};

#undef ITEM
#define ITEM(x) x;
struct s {
LIST
};

 

[Chris Dollin]

I like that approach:

#define LIST ITEM(a),ITEM(b),ITEM(c)

#define ITEM(x) x,
enum e {
LIST,
NUM_ENTRIES
};

#undef ITEM
#define ITEM(x) x;
struct s {
LIST
};

I don't like that implementation of it.

 

[Thad Smith]

I don't like that implementation of it.

It's a little messy, but the best I can think of to have multiple uses
of a single list using only C. You could do something nicer with an
external preprocessor. Feel free to contribute your own solution.