Re: warning: pasting would not give a valid preprocessing token

[Zack Weinberg <zack@wolery.cumb.org>]

On Fri, Aug 11, 2000 at 11:58:11PM -0400, Byron Stanoszek wrote:
> On 11 Aug 2000, Geoff Keating wrote:
> 
> > Byron Stanoszek <gandalf@winds.org> writes:
> > 
> > > I've seen this warning in many of my .c files when compiling
> > > with versions of 2.96 from mid-july and newer.. has anyone else
> > > seen this before, know what it is, and how to fix it?
> > > 
> > > warning: pasting would not give a valid preprocessing token
> > 
> > It means you're writing something like
> > 
> > #define paste(a, b) a##b
> > paste(*,foo)
> > 
> > because '*foo' is not a token, the tokens you want are '*' and 'foo'.
> > The solution is to replace the ## with a space.
> 
> Strange, but true. I see the problem now. I have a #define like this:
> 
> /* tprintf(): prints to a temporary variable 16k in size */
> extern char global_buff[16384];
> #define tprintf(format, args...) (sprintf(global_buff, format, ## args), \
>                                   (char *)global_buff)
> 
> But in my .c file, I use string concatenation like this:
> 
>   notify(player, tprintf("Your knowledge of %s is too low to speak "
>          "it fluently.", language[ptr->num].name));
> 
> Can you tell me what the best way there is to get around that?

Very recent versions of gcc should not give that warning for the
specific case of , ## <rest argument>.

You could also write your tprintf() macro like this:

#define tprintf(args...) (snprintf(buff, BUFSIZ, args), (char *)buff)

you'll still get an error for tprintf(/* nothing */) but
tprintf("string") will be fine.

zw