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Date: Fri, 27 Mar 2009 09:53:32 +0100
From: Bertrand Jeannet <Bertrand.Jeannet@inrialpes.fr>
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To: caml-list@yquem.inria.fr
Subject: printf "%a" vs sprintf "%a"
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X-Spam: no; 0.00; jeannet:01 jeannet:01 inrialpes:01 printf:01 sprintf:01 ocaml:01 sprintf:01 printf:01 buffer:01 buffer:01 fprintf:01 val:01 fmt:01 fmt:01 defined:02 


For people that do not use OCaml batteries, a sprintf function similar 
to  (Printf|Format).printf can be defined using kfprintf:

let sprintf format =
   let buffer = Buffer.create 512 in
   let fmt = Format.formatter_of_buffer buffer in
   Format.kfprintf
     (begin fun fmt ->
       Format.pp_print_flush fmt ();
       let s = Buffer.contents buffer in
       Buffer.clear buffer;
       s
     end)
     fmt
     format

The types are different:
Format.fprintf : Format.formatter -> ('a, Format.formatter, unit, unit) 
format4 -> 'a
val sprintf : ('a, Format.formatter, unit, string) format4 -> 'a = <fun>

but that is normal, as sprintf should return a string.

Bertrand Jeannet