SPRINTF SPAN SRAND
SPRINTF ( args ... format$ dest$ -- len-dest )  
<PFE-SMART>
just like the standard sprintf() function in C, but the format is a counted string and accepts %#s to be the format-symbol for a forth-counted string. The result is a zeroterminated string at dest$ having a length being returned. To create a forth-counted string, you could use: 
   variable A 256 ALLOT
   15 " example" " the %#s value is %i" A 1+ SPRINTF A C!
   A COUNT TYPE

reference: p4_sprintf in ../src/yours.c:0497, export CO SPRINTF