[avr-libc-dev] Implementing the vprintf "%*s" and "%.*s" formats

[Paul \"LeoNerd\" Evans]

I often find it useful to be able to print a character buffer of
dynamically-known size by using some variant on

  printf("%.*s", len, buf);

It appears to me that avr-libc doesn't recognise this particular flag.
It is documented that

  The variable width or precision field (an asterisk * symbol) is not
  realized and will to abort the output.

But it's unclear from this whether the absence is deliberate, or simply
not implemented yet.

Would folk be amenable to a patch to add this feature? I have an
(as-yet untested) attempt at it it. I don't think it would massively
increase code size, and it doesn't consume any more RAM at runtime.

But I thought I'd ask, in case there's some specific reason for its
absence.

-----

=== modified file 'libc/stdio/vfprintf.c'
--- libc/stdio/vfprintf.c       2017-10-17 19:56:22 +0000
+++ libc/stdio/vfprintf.c       2017-10-17 19:57:23 +0000
@@ -344,6 +344,12 @@
                    flags |= FL_WIDTH;
                    continue;
                }
+               if (c == '*') {
+                   if (flags & FL_PREC)
+                       prec = va_arg(ap, int);
+                   else
+                       width = va_arg(ap, int);
+               }
                if (c == '.') {
                    if (flags & FL_PREC)
                        goto ret;


-- 
Paul "LeoNerd" Evans

address@hidden      |  https://metacpan.org/author/PEVANS
http://www.leonerd.org.uk/  |  https://www.tindie.com/stores/leonerd/

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