diff --git a/stdlib/format.ml b/stdlib/format.ml
index 2fabff2e7..f4b519c8d 100644
--- a/stdlib/format.ml
+++ b/stdlib/format.ml
@@ -910,14 +910,16 @@ and set_tags =
 
  **************************************************************)
 
+module Sformat = Printf.Sformat;;
+
 (* Error messages when processing formats. *)
 
 (* Trailer: giving up at character number ... *)
 let giving_up mess fmt i =
-  "fprintf: " ^ mess ^ " ``" ^ fmt ^ "'', \
+  "fprintf: " ^ mess ^ " ``" ^ Sformat.to_string fmt ^ "'', \
    giving up at character number " ^ string_of_int i ^
-  (if i < String.length fmt
-   then " (" ^ String.make 1 fmt.[i] ^ ")."
+  (if i < Sformat.length fmt
+   then " (" ^ String.make 1 (Sformat.get fmt i) ^ ")."
    else String.make 1 '.');;
 
 (* When an invalid format deserves a special error explanation. *)
@@ -963,8 +965,6 @@ let implode_rev s0 = function
   | [] -> s0
   | l -> String.concat "" (List.rev (s0 :: l));;
 
-external format_to_string : ('a, 'b, 'c, 'd) format4 -> string = "%identity";;
-
 (* [fprintf_out] is the printf-like function generator: given the
    - [to_s] flag that tells if we are printing into a string,
    - the [get_out] function that has to be called at the end of formatting,
@@ -975,8 +975,7 @@ external format_to_string : ('a, 'b, 'c, 'd) format4 -> string = "%identity";;
    applications of [fprintf_out]. *)
 let mkprintf to_s get_out =
   let rec kprintf k fmt =
-    let fmt = format_to_string fmt in
-    let len = String.length fmt in
+    let len = Sformat.length fmt in
 
     let kpr fmt v =
       let ppf = get_out fmt in
@@ -996,13 +995,13 @@ let mkprintf to_s get_out =
 
       let rec doprn n i =
         if i >= len then Obj.magic (k ppf) else
-        match fmt.[i] with
+        match Sformat.get fmt i with
         | '%' ->
             Printf.scan_format fmt v n i cont_s cont_a cont_t cont_f cont_m
         | '@' ->
             let i = succ i in
             if i >= len then invalid_format fmt i else
-            begin match fmt.[i] with
+            begin match Sformat.get fmt i with
             | '[' ->
                do_pp_open_box ppf n (succ i)
             | ']' ->
@@ -1065,7 +1064,7 @@ let mkprintf to_s get_out =
 
       and get_int n i c =
        if i >= len then invalid_integer fmt i else
-       match fmt.[i] with
+       match Sformat.get fmt i with
        | ' ' -> get_int n (succ i) c
        | '%' ->
           let cont_s n s i = c (format_int_of_string fmt i s) n i
@@ -1077,33 +1076,34 @@ let mkprintf to_s get_out =
        | _ ->
           let rec get j =
            if j >= len then invalid_integer fmt j else
-           match fmt.[j] with
+           match Sformat.get fmt j with
            | '0' .. '9' | '-' -> get (succ j)
            | _ ->
              let size =
              if j = i then size_of_int 0 else
-                format_int_of_string fmt j (String.sub fmt i (j - i)) in
+                let s = Sformat.sub fmt i (j - i) in
+                format_int_of_string fmt j s in
              c size n j in
           get i
 
       and skip_gt i =
        if i >= len then invalid_format fmt i else
-       match fmt.[i] with
+       match Sformat.get fmt i with
        | ' ' -> skip_gt (succ i)
        | '>' -> succ i
        | _ -> invalid_format fmt i
 
       and get_box_kind i =
        if i >= len then Pp_box, i else
-       match fmt.[i] with
+       match Sformat.get fmt i with
        | 'h' ->
           let i = succ i in
           if i >= len then Pp_hbox, i else
-          begin match fmt.[i] with
+          begin match Sformat.get fmt i with
           | 'o' ->
              let i = succ i in
              if i >= len then format_invalid_arg "bad box format" fmt i else
-             begin match fmt.[i] with
+             begin match Sformat.get fmt i with
              | 'v' -> Pp_hovbox, succ i
              | c ->
                 format_invalid_arg
@@ -1118,11 +1118,11 @@ let mkprintf to_s get_out =
       and get_tag_name n i c =
        let rec get accu n i j =
         if j >= len
-        then c (implode_rev (String.sub fmt i (j - i)) accu) n j else
-        match fmt.[j] with
-        | '>' -> c (implode_rev (String.sub fmt i (j - i)) accu) n j
+        then c (implode_rev (Sformat.sub fmt i (j - i)) accu) n j else
+        match Sformat.get fmt j with
+        | '>' -> c (implode_rev (Sformat.sub fmt i (j - i)) accu) n j
         | '%' ->
-          let s0 = String.sub fmt i (j - i) in
+          let s0 = Sformat.sub fmt i (j - i) in
           let cont_s n s i = get (s :: s0 :: accu) n i i
           and cont_a n printer arg i =
             let s =
@@ -1146,7 +1146,7 @@ let mkprintf to_s get_out =
 
       and do_pp_break ppf n i =
        if i >= len then begin pp_print_space ppf (); doprn n i end else
-       match fmt.[i] with
+       match Sformat.get fmt i with
        | '<' ->
           let rec got_nspaces nspaces n i =
             get_int n i (got_offset nspaces)
@@ -1158,7 +1158,7 @@ let mkprintf to_s get_out =
 
       and do_pp_open_box ppf n i =
        if i >= len then begin pp_open_box_gen ppf 0 Pp_box; doprn n i end else
-       match fmt.[i] with
+       match Sformat.get fmt i with
        | '<' ->
           let kind, i = get_box_kind (succ i) in
           let got_size size n i =
@@ -1169,7 +1169,7 @@ let mkprintf to_s get_out =
 
       and do_pp_open_tag ppf n i =
        if i >= len then begin pp_open_tag ppf ""; doprn n i end else
-       match fmt.[i] with
+       match Sformat.get fmt i with
        | '<' ->
           let got_name tag_name n i =
             pp_open_tag ppf tag_name;
diff --git a/stdlib/printf.ml b/stdlib/printf.ml
index fe42ec861..1acb41b6e 100644
--- a/stdlib/printf.ml
+++ b/stdlib/printf.ml
@@ -13,14 +13,33 @@
 
 (* $Id$ *)
 
-external format_int: string -> int -> string = "caml_format_int"
-external format_int32: string -> int32 -> string = "caml_int32_format"
+external format_float: string -> float -> string
+  = "caml_format_float"
+external format_int: string -> int -> string
+  = "caml_format_int"
+external format_int32: string -> int32 -> string
+  = "caml_int32_format"
 external format_nativeint: string -> nativeint -> string
-                         = "caml_nativeint_format"
-external format_int64: string -> int64 -> string = "caml_int64_format"
-external format_float: string -> float -> string = "caml_format_float"
+  = "caml_nativeint_format"
+external format_int64: string -> int64 -> string
+  = "caml_int64_format"
 
-external format_to_string: ('a, 'b, 'c, 'd) format4 -> string = "%identity"
+module Sformat = struct
+  external unsafe_to_string : ('a, 'b, 'c, 'd) format4 -> string
+    = "%identity"
+  external length : ('a, 'b, 'c, 'd) format4 -> int
+    = "%string_length"
+  external get : ('a, 'b, 'c, 'd) format4 -> int -> char
+    = "%string_safe_get"
+  external unsafe_get : ('a, 'b, 'c, 'd) format4 -> int -> char
+    = "%string_unsafe_get"
+(*  external set : ('a, 'b, 'c, 'd) format4 -> int -> char -> unit
+    = "%string_safe_set"
+  external unsafe_set : ('a, 'b, 'c, 'd) format4 -> int -> char -> unit
+    = "%string_unsafe_set" *)
+  let sub fmt idx len = String.sub (unsafe_to_string fmt) idx len
+  let to_string fmt = sub fmt 0 (length fmt)
+end;;
 
 type index;;
 
@@ -32,28 +51,33 @@ let succ_index = add_int_index 1;;
 (* Litteral position are one-based (hence pred p instead of p). *)
 let index_of_litteral_position p = index_of_int (pred p);;
 
-let bad_conversion fmt i c =
+let bad_conversion sfmt i c =
   invalid_arg
     ("printf: bad conversion %" ^ String.make 1 c ^ ", at char number " ^
-     string_of_int i ^ " in format string ``" ^ fmt ^ "''");;
+     string_of_int i ^ " in format string ``" ^ sfmt ^ "''");;
+
+let bad_conversion_format fmt i c =
+  bad_conversion (Sformat.to_string fmt) i c;;
 
 let incomplete_format fmt =
   invalid_arg
-    ("printf: premature end of format string ``" ^ fmt ^ "''");;
+    ("printf: premature end of format string ``" ^
+     Sformat.to_string fmt ^ "''");;
 
 (* Parses a format to return the specified length and the padding direction. *)
-let parse_format fmt =
+let parse_format sfmt =
   let rec parse neg i =
-    if i >= String.length fmt then (0, neg) else
-    match String.unsafe_get fmt i with
+    if i >= String.length sfmt then (0, neg) else
+    match String.unsafe_get sfmt i with
     | '1'..'9' ->
-        (int_of_string (String.sub fmt i (String.length fmt - i - 1)),
+        (int_of_string
+           (String.sub sfmt i (String.length sfmt - i - 1)),
          neg)
     | '-' ->
         parse true (succ i)
     | _ ->
         parse neg (succ i) in
-  try parse false 1 with Failure _ -> bad_conversion fmt 0 's'
+  try parse false 1 with Failure _ -> bad_conversion sfmt 0 's'
 
 (* Pad a (sub) string into a blank string of length [p],
    on the right if [neg] is true, on the left otherwise. *)
@@ -68,18 +92,19 @@ let pad_string pad_char p neg s i len =
 
 (* Format a string given a %s format, e.g. %40s or %-20s.
    To do: ignore other flags (#, +, etc)? *)
-let format_string fmt s =
-  let (p, neg) = parse_format fmt in
-  pad_string ' ' p neg s 0 (String.length s)
+let format_string sfmt s =
+  let (p, neg) = parse_format sfmt in
+  pad_string ' ' p neg s 0 (String.length s);;
 
-(* Extract a %format from [fmt] between [start] and [stop] inclusive.
-   '*' in the format are replaced by integers taken from the [widths] list. *)
+(* Extract a format string out of [fmt] between [start] and [stop] inclusive.
+   '*' in the format are replaced by integers taken from the [widths] list.
+   extract_format returns a string. *)
 let extract_format fmt start stop widths =
   let skip_positional_spec start =
-    match String.unsafe_get fmt start with
+    match Sformat.unsafe_get fmt start with
     | '0'..'9' ->
       let rec skip_int_litteral i =
-        match String.unsafe_get fmt i with
+        match Sformat.unsafe_get fmt i with
         | '0'..'9' -> skip_int_litteral (succ i)
         | '$' -> succ i
         | _ -> start in
@@ -90,7 +115,7 @@ let extract_format fmt start stop widths =
   Buffer.add_char b '%';
   let rec fill_format i widths =
     if i <= stop then
-      match (String.unsafe_get fmt i, widths) with
+      match (Sformat.unsafe_get fmt i, widths) with
       | ('*', h :: t) ->
         Buffer.add_string b (string_of_int h);
         let i = skip_positional_spec (succ i) in
@@ -102,10 +127,13 @@ let extract_format fmt start stop widths =
   fill_format start (List.rev widths);
   Buffer.contents b;;
 
-let format_int_with_conv conv fmt i =
+let extract_format_int conv fmt start stop widths =
+   let sfmt = extract_format fmt start stop widths in
    match conv with
-   | 'n' | 'N' -> fmt.[String.length fmt - 1] <- 'u'; format_int fmt i
-   | _ -> format_int fmt i
+   | 'n' | 'N' ->
+     sfmt. [String.length sfmt - 1] <- 'u';
+     sfmt
+   | _ -> sfmt;;
 
 (* Returns the position of the last character of the meta format
    string, starting from position [i], inside a given format [fmt].
@@ -114,34 +142,36 @@ let format_int_with_conv conv fmt i =
    %) (when [conv = '(']). Hence, [sub_format] returns the index of
    the character ')' or '}' that ends the meta format, according to
    the character [conv]. *)
-let sub_format incomplete_format bad_conversion conv fmt i =
-  let len = String.length fmt in
+let sub_format incomplete_format bad_conversion_format conv fmt i =
+  let len = Sformat.length fmt in
   let rec sub_fmt c i =
     let close = if c = '(' then ')' else (* '{' *) '}' in
     let rec sub j =
        if j >= len then incomplete_format fmt else
-       match fmt.[j] with
+       match Sformat.get fmt j with
        | '%' -> sub_sub (succ j)
        | _ -> sub (succ j)
     and sub_sub j =
        if j >= len then incomplete_format fmt else
-       match fmt.[j] with
+       match Sformat.get fmt j with
        | '(' | '{' as c ->
          let j = sub_fmt c (succ j) in sub (succ j)
        | '}' | ')' as c ->
-         if c = close then j else bad_conversion fmt i c
+         if c = close then j else bad_conversion_format fmt i c
        | _ -> sub (succ j) in
     sub i in
   sub_fmt conv i;;
 
-let sub_format_for_printf = sub_format incomplete_format bad_conversion;;
+let sub_format_for_printf conv =
+  sub_format incomplete_format bad_conversion_format conv;;
 
 let iter_on_format_args fmt add_conv add_char =
-  let lim = String.length fmt - 1 in
+
+  let lim = Sformat.length fmt - 1 in
 
   let rec scan_flags skip i =
     if i > lim then incomplete_format fmt else
-    match String.unsafe_get fmt i with
+    match Sformat.unsafe_get fmt i with
     | '*' -> scan_flags skip (add_conv skip i 'i')
     | '$' -> scan_flags skip (succ i)
     | '#' | '-' | ' ' | '+' -> scan_flags skip (succ i)
@@ -151,7 +181,7 @@ let iter_on_format_args fmt add_conv add_char =
     | _ -> scan_conv skip i
   and scan_conv skip i =
     if i > lim then incomplete_format fmt else
-    match String.unsafe_get fmt i with
+    match Sformat.unsafe_get fmt i with
     | '%' | '!' -> succ i
     | 's' | 'S' | '[' -> add_conv skip i 's'
     | 'c' | 'C' -> add_conv skip i 'c'
@@ -162,7 +192,7 @@ let iter_on_format_args fmt add_conv add_char =
     | 'l' | 'n' | 'L' as conv ->
         let j = succ i in
         if j > lim then add_conv skip i 'i' else begin
-          match fmt.[j] with
+          match Sformat.get fmt j with
           | 'd' | 'i' | 'o' | 'x' | 'X' | 'u' ->
             add_char (add_conv skip i conv) 'i'
           | c -> add_conv skip i 'i' end
@@ -172,7 +202,7 @@ let iter_on_format_args fmt add_conv add_char =
       let j = sub_format_for_printf conv fmt i in
       (* Add the meta specification anyway. *)
       let rec loop i =
-        if i < j - 1 then loop (add_char i fmt.[i]) in
+        if i < j - 1 then loop (add_char i (Sformat.get fmt i)) in
       loop i;
       scan_conv skip j
     | '(' as conv ->
@@ -181,11 +211,11 @@ let iter_on_format_args fmt add_conv add_char =
          anyway. *)
       scan_fmt (add_conv skip i conv)
     | '}' | ')' as conv -> add_conv skip i conv
-    | conv -> bad_conversion fmt i conv
+    | conv -> bad_conversion_format fmt i conv
 
   and scan_fmt i =
     if i < lim then
-     if fmt.[i] = '%'
+     if Sformat.get fmt i = '%'
      then scan_fmt (scan_flags false (succ i))
      else scan_fmt (succ i)
     else i in
@@ -197,7 +227,7 @@ let iter_on_format_args fmt add_conv add_char =
    It also checks the well-formedness of the format string.
    For instance, [summarize_format_type "A number %d\n"] is "%i". *)
 let summarize_format_type fmt =
-  let len = String.length fmt in
+  let len = Sformat.length fmt in
   let b = Buffer.create len in
   let add_char i c = Buffer.add_char b c; succ i in
   let add_conv skip i c =
@@ -278,10 +308,10 @@ type param_spec = Spec_none | Spec_index of index;;
    problems: the type would be dependant of the {\em value} of an integer
    argument to printf. *)
 let scan_positional_spec fmt got_pos n i =
-  match String.unsafe_get fmt i with
+  match Sformat.unsafe_get fmt i with
   | '0'..'9' as d ->
     let rec get_int_litteral accu j =
-      match String.unsafe_get fmt j with
+      match Sformat.unsafe_get fmt j with
       | '0'..'9' as d ->
         get_int_litteral (10 * accu + (int_of_char d - 48)) (succ j)
       | '$' ->
@@ -320,8 +350,8 @@ let get_index spec n =
    "next pos" is the position in [fmt] of the first character following
    the %format in [fmt]. *)
 
-(* Note: here, rather than test explicitly against [String.length fmt]
-   to detect the end of the format, we use [String.unsafe_get] and
+(* Note: here, rather than test explicitly against [Sformat.length fmt]
+   to detect the end of the format, we use [Sformat.unsafe_get] and
    rely on the fact that we'll get a "nul" character if we access
    one past the end of the string.  These "nul" characters are then
    caught by the [_ -> bad_conversion] clauses below.
@@ -335,7 +365,7 @@ let scan_format fmt args n pos cont_s cont_a cont_t cont_f cont_m =
     scan_positional_spec fmt got_pos n i
 
   and scan_flags spec n widths i =
-    match String.unsafe_get fmt i with
+    match Sformat.unsafe_get fmt i with
     | '*' ->
       let got_pos wspec i =
         let (width : int) = get_arg wspec n in
@@ -346,7 +376,7 @@ let scan_format fmt args n pos cont_s cont_a cont_t cont_f cont_m =
     | _ -> scan_conv spec n widths i
 
   and scan_conv spec n widths i =
-    match String.unsafe_get fmt i with
+    match Sformat.unsafe_get fmt i with
     | '%' ->
       cont_s n "%" (succ i)
     | 's' | 'S' as conv ->
@@ -364,7 +394,8 @@ let scan_format fmt args n pos cont_s cont_a cont_t cont_f cont_m =
       cont_s (next_index spec n) s (succ i)
     | 'd' | 'i' | 'o' | 'x' | 'X' | 'u' | 'N' as conv ->
       let (x : int) = get_arg spec n in
-      let s = format_int_with_conv conv (extract_format fmt pos i widths) x in
+      let s =
+        format_int (extract_format_int conv fmt pos i widths) x in
       cont_s (next_index spec n) s (succ i)
     | 'f' | 'e' | 'E' | 'g' | 'G' | 'F' as conv ->
       let (x : float) = get_arg spec n in
@@ -387,7 +418,7 @@ let scan_format fmt args n pos cont_s cont_a cont_t cont_f cont_m =
       let printer = get_arg spec n in
       cont_t (next_index spec n) printer (succ i)
     | 'l' | 'n' | 'L' as conv ->
-      begin match String.unsafe_get fmt (succ i) with
+      begin match Sformat.unsafe_get fmt (succ i) with
       | 'd' | 'i' | 'o' | 'x' | 'X' | 'u' ->
         let s =
           match conv with
@@ -403,10 +434,8 @@ let scan_format fmt args n pos cont_s cont_a cont_t cont_f cont_m =
         cont_s (next_index spec n) s (i + 2)
       | _ ->
         let (x : int) = get_arg spec n in
-        cont_s
-          (next_index spec n)
-          (format_int_with_conv 'n' (extract_format fmt pos i widths) x)
-          (succ i)
+        let s = format_int (extract_format_int 'n' fmt pos i widths) x in
+        cont_s (next_index spec n) s (succ i)
       end
     | '!' -> cont_f n (succ i)
     | '{' | '(' as conv (* ')' '}' *) ->
@@ -417,31 +446,31 @@ let scan_format fmt args n pos cont_s cont_a cont_t cont_f cont_m =
         (* Just print the format argument as a specification. *)
         cont_s
           (next_index spec n)
-          (summarize_format_type (format_to_string xf))
+          (summarize_format_type xf)
           j else
         (* Use the format argument instead of the format specification. *)
         cont_m (next_index spec n) xf j
     | (* '(' *) ')' ->
       cont_s n "" (succ i)
     | conv ->
-      bad_conversion fmt i conv in
+      bad_conversion_format fmt i conv in
 
   scan_positional n [] (succ pos);;
 
 let mkprintf str get_out outc outs flush k fmt =
 
-  let fmt = format_to_string fmt in
+(*  let fmt = Sformat.length fmt in*)
   (* out is global to this invocation of pr, and must be shared by all its
      recursive calls (fif) any. *)
   let out = get_out fmt in
 
   let rec pr k n fmt v =
 
-    let len = String.length fmt in
+    let len = Sformat.length fmt in
 
     let rec doprn n i =
        if i >= len then Obj.magic (k out) else
-       match String.unsafe_get fmt i with
+       match Sformat.unsafe_get fmt i with
        | '%' -> scan_format fmt v n i cont_s cont_a cont_t cont_f cont_m
        |  c  -> outc out c; doprn n (succ i)
      and cont_s n s i =
@@ -461,8 +490,8 @@ let mkprintf str get_out outc outs flush k fmt =
      and cont_f n i =
        flush out; doprn n i
      and cont_m n xf i =
-       let m = add_int_index (nargs_of_format_type (format_to_string xf)) n in
-       pr (Obj.magic (fun _ -> doprn m i)) n (format_to_string xf) v in
+       let m = add_int_index (nargs_of_format_type xf) n in
+       pr (Obj.magic (fun _ -> doprn m i)) n xf v in
 
      doprn n 0 in
 
@@ -481,7 +510,7 @@ let kbprintf k b =
 let bprintf b = kbprintf ignore b
 
 let get_buff fmt =
-  let len = 2 * String.length fmt in
+  let len = 2 * Sformat.length fmt in
   Buffer.create len;;
 
 let get_contents b =
diff --git a/stdlib/printf.mli b/stdlib/printf.mli
index fe4b8b2f8..d612f4ad3 100644
--- a/stdlib/printf.mli
+++ b/stdlib/printf.mli
@@ -142,15 +142,34 @@ type index;;
 
 external index_of_int : int -> index = "%identity";;
 
-val scan_format : string -> 'a array -> index -> int ->
-  (index -> string -> int -> 'b) ->
-  (index -> 'c -> 'd -> int -> 'b) ->
-  (index -> 'e -> int -> 'b) ->
-  (index -> int -> 'b) ->
-  (index -> ('h, 'i, 'j, 'k) format4 -> int -> 'b) -> 'b
+module Sformat : sig
+  external unsafe_to_string : ('a, 'b, 'c, 'd) format4 -> string
+    = "%identity"
+  external length : ('a, 'b, 'c, 'd) format4 -> int
+    = "%string_length"
+  external get : ('a, 'b, 'c, 'd) format4 -> int -> char
+    = "%string_safe_get"
+  external unsafe_get : ('a, 'b, 'c, 'd) format4 -> int -> char
+    = "%string_unsafe_get"
+  val sub : ('a, 'b, 'c, 'd) format4 -> int -> int -> string
+  val to_string : ('a, 'b, 'c, 'd) format4 -> string
+end
+
+val scan_format : ('a, 'b, 'c, 'd) format4 ->
+    'e array ->
+    index ->
+    int ->
+    (index -> string -> int -> 'f) ->
+    (index -> 'g -> 'h -> int -> 'f) ->
+    (index -> 'i -> int -> 'f) ->
+    (index -> int -> 'f) ->
+    (index -> ('j, 'k, 'l, 'm) format4 -> int -> 'f) -> 'f
 
 val sub_format :
-  (string -> int) -> (string -> int -> char -> int) ->
-  char -> string -> int -> int
-val summarize_format_type : string -> string
-val kapr : (string -> Obj.t array -> 'a) -> string -> 'a
+    (('a, 'b, 'c, 'd) format4 -> int) ->
+    (('a, 'b, 'c, 'd) format4 -> int -> char -> int) ->
+    char -> ('a, 'b, 'c, 'd) format4 -> int -> int
+val summarize_format_type : ('a, 'b, 'c, 'd) format4 -> string
+val kapr :
+    (('a, 'b, 'c, 'd) format4 -> Obj.t array -> 'e) ->
+    ('a, 'b, 'c, 'd) format4 -> 'e
diff --git a/stdlib/scanf.ml b/stdlib/scanf.ml
index 030075ba3..a0a49c061 100644
--- a/stdlib/scanf.ml
+++ b/stdlib/scanf.ml
@@ -217,7 +217,11 @@ let from_function = create "function input";;
 (* Perform bufferized input to improve efficiency. *)
 let file_buffer_size = ref 1024;;
 
-let from_file_channel fname ic =
+(* To close a channel at end of input. *)
+let scan_close_at_end ic = close_in ic; raise End_of_file;;
+
+(* Scan from an input channel. *)
+let from_ic scan_close_ic fname ic =
   let len = !file_buffer_size in
   let buf = String.create len in
   let i = ref 0 in
@@ -225,29 +229,90 @@ let from_file_channel fname ic =
   let next () =
     if !i < !lim then begin let c = buf.[!i] in incr i; c end else begin
       lim := input ic buf 0 len;
-      if !lim = 0 then raise End_of_file else begin
+      if !lim = 0 then scan_close_ic ic else begin
         i := 1;
         buf.[0]
       end
     end in
   create fname next;;
 
-let from_file fname = from_file_channel fname (open_in fname);;
-let from_file_bin fname = from_file_channel fname (open_in_bin fname);;
+let from_ic_close_at_end = from_ic scan_close_at_end;;
 
-let from_input_channel fname ic =
-  let next () = input_char ic in
-  create fname next;;
+let from_file fname = from_ic_close_at_end fname (open_in fname);;
+let from_file_bin fname = from_ic_close_at_end fname (open_in_bin fname);;
 
-let from_channel = from_input_channel "input channel";;
+(* Input channel [ic] is not allocated here, hence it may be shared (two
+   functions of the program may successively read from it). Furthermore, the
+   user may define more than one scanning buffer reading from the same [ic]
+   channel.
 
-(* The scanning buffer reading from [stdin].*)
-let stdib = from_input_channel "stdin" stdin;;
+   However, we cannot prevent scanf to use one lookahead character if needed;
+   this implies that multiple functions alternatively scanning the same [ic]
+   channel will miss characters from time to time, due to unnoticed look ahead
+   characters, silently read from [ic] (hence no more available for reading)
+   and retained inside the scanning buffer for correct scanning from the same
+   scanning buffer. This phenomenon is even worse in case of multiple
+   definition of scanning buffers from the same [ic].
+
+   Hence, we do bufferize characters to create a scnning buffer from an input
+   channel in order to preserve the same semantics as other from_* functions
+   above: two successive calls to the scanner will work appropriately, since
+   the bufferized character (if any) will be retained inside the scanning
+   buffer from a call to the next one.
+
+   Otherwise, if we do not bufferize characters, we will loose the clearly
+   correct scanning behaviour even for the simple regular case, when we scan
+   the (possibly shared) channel [ic] using a unique function, while not
+   gaining anything for multiple functions reading from [ic] or multiple
+   allocation of scanning buffers reading from the same [ic].
+
+   A more ambitious fix could be to have a memo scanning buffer allocation
+   for reading from input channel not allocated from within Scanf. *)
+
+let scan_at_end ic = raise End_of_file;;
+
+let from_channel = from_ic scan_at_end "input channel";;
+
+(* The scanning buffer reading from [stdin].
+   One could try to define stdib as from_channel stdin,
+   but unfortunately the toplevel interaction would be wrong.
+   This is due to some kind of ``race condition'' when reading from stdin,
+   since the interactive compiler and scanf will simultaneously read the
+   material they need from stdin; then, confusion will result from what should
+   be read by the toplevel and what should be read by scanf.
+   This is even more complicated by the one character lookahead that scanf
+   is sometimes obliged to maintain: the lookahead character will be available
+   for the next (scanf) entry, seamingly coming from nowhere.
+   Also no End_of_file is raised when reading from stdin: if not enough
+   characters have been read, we simply ask to read more. *)
+(*let stdib =
+  let buf = ref ""
+  and len = ref 0 in
+  let mk_buff l =
+    buf := String.create l;
+    len := l in
+  let i = ref 0 in
+  let rec next () =
+    if !i < !len then begin let c = !buf.[!i] in incr i; c end else
+    let s = input_line stdin in
+    let ls = String.length s in
+    if ls > !len then mk_buff ls;
+    String.blit s 0 !buf 0 ls;
+    i := 0;
+    next () in
+  create "stdin" next;;
+*)
+let stdib = from_ic scan_at_end "stdin" stdin;;
 
 end;;
 
 (* Formatted input functions. *)
 
+module Sformat = Printf.Sformat;;
+
+external string_to_format :
+ string -> ('a, 'b, 'c, 'd) format4 = "%identity";;
+
 (* Reporting errors. *)
 exception Scan_failure of string;;
 
@@ -267,11 +332,12 @@ let bad_conversion fmt i c =
   invalid_arg
     (Printf.sprintf
        "scanf: bad conversion %%%c, at char number %i \
-        in format string ``%s''" c i fmt);;
+        in format string ``%s''" c i (Sformat.to_string fmt));;
 
 let incomplete_format fmt =
   invalid_arg
-    (Printf.sprintf "scanf: premature end of format string ``%s''" fmt);;
+    (Printf.sprintf "scanf: premature end of format string ``%s''"
+       (Sformat.to_string fmt));;
 
 let bad_float () = bad_input "no dot or exponent part found in float token";;
 
@@ -283,7 +349,8 @@ let format_mismatch fmt1 fmt2 ib =
 
 (* Checking that 2 format string are type compatible. *)
 let compatible_format_type fmt1 fmt2 =
-  Printf.summarize_format_type fmt1 = Printf.summarize_format_type fmt2;;
+  Printf.summarize_format_type (string_to_format fmt1) =
+  Printf.summarize_format_type (string_to_format fmt2);;
 
 (* Checking that [c] is indeed in the input, then skips it.
    In this case, the character c has been explicitely specified in the
@@ -347,9 +414,12 @@ let token_float ib = float_of_string (Scanning.token ib);;
    since those modules are not available to Scanf.
    However, we can bind and use the corresponding primitives that are
    available in the runtime. *)
-external nativeint_of_string: string -> nativeint = "caml_nativeint_of_string";;
-external int32_of_string : string -> int32 = "caml_int32_of_string";;
-external int64_of_string : string -> int64 = "caml_int64_of_string";;
+external nativeint_of_string : string -> nativeint
+  = "caml_nativeint_of_string";;
+external int32_of_string : string -> int32
+  = "caml_int32_of_string";;
+external int64_of_string : string -> int64
+  = "caml_int64_of_string";;
 
 let token_nativeint conv ib = nativeint_of_string (token_int_literal conv ib);;
 let token_int32 conv ib = int32_of_string (token_int_literal conv ib);;
@@ -648,29 +718,29 @@ type char_set =
 
 (* Char sets are read as sub-strings in the format string. *)
 let read_char_set fmt i =
-  let lim = String.length fmt - 1 in
+  let lim = Sformat.length fmt - 1 in
 
   let rec find_in_set j =
     if j > lim then incomplete_format fmt else
-    match fmt.[j] with
+    match Sformat.get fmt j with
     | ']' -> j
     | c -> find_in_set (j + 1)
 
   and find_set i =
     if i > lim then incomplete_format fmt else
-    match fmt.[i] with
+    match Sformat.get fmt i with
     | ']' -> find_in_set (i + 1)
     | c -> find_in_set i in
 
   if i > lim then incomplete_format fmt else
-  match fmt.[i] with
+  match Sformat.get fmt i with
   | '^' ->
      let i = i + 1 in
      let j = find_set i in
-     j, Neg_set (String.sub fmt i (j - i))
+     j, Neg_set (Sformat.sub fmt i (j - i))
   | _ ->
      let j = find_set i in
-     j, Pos_set (String.sub fmt i (j - i));;
+     j, Pos_set (Sformat.sub fmt i (j - i));;
 
 (* Char sets are now represented as bitvects that are represented as
    byte strings. *)
@@ -874,11 +944,6 @@ let rec skip_whites ib =
     | _ -> ()
   end;;
 
-external format_to_string :
- ('a, 'b, 'c, 'd) format4 -> string = "%identity";;
-external string_to_format :
- string -> ('a, 'b, 'c, 'd) format4 = "%identity";;
-
 (* The [kscanf] main scanning function.
    It takes as arguments:
      - an input buffer [ib] from which to read characters,
@@ -899,8 +964,8 @@ external string_to_format :
    aborts and applies the scanning buffer and a string that explains
    the error to the error handling function [ef] (the error continuation). *)
 let kscanf ib ef fmt f =
-  let fmt = format_to_string fmt in
-  let lim = String.length fmt - 1 in
+
+  let lim = Sformat.length fmt - 1 in
 
   let return v = Obj.magic v () in
   let delay f x () = f x in
@@ -909,7 +974,7 @@ let kscanf ib ef fmt f =
 
   let rec scan_fmt f i =
     if i > lim then f else
-    match fmt.[i] with
+    match Sformat.get fmt i with
     | ' ' -> skip_whites ib; scan_fmt f (i + 1)
     | '%' ->
         if i > lim then incomplete_format fmt else
@@ -917,13 +982,13 @@ let kscanf ib ef fmt f =
     | '@' ->
         let i = i + 1 in
         if i > lim then incomplete_format fmt else begin
-        check_char ib fmt.[i];
+        check_char ib (Sformat.get fmt i);
         scan_fmt f (i + 1) end
     | c -> check_char ib c; scan_fmt f (i + 1)
 
   and scan_conversion skip max f i =
     let stack = if skip then no_stack else stack in
-    match fmt.[i] with
+    match Sformat.get fmt i with
     | '%' as conv ->
         check_char ib conv; scan_fmt f (i + 1)
     | 'c' when max = 0 ->
@@ -961,14 +1026,14 @@ let kscanf ib ef fmt f =
     | 'l' | 'n' | 'L' as conv ->
         let i = i + 1 in
         if i > lim then scan_fmt (stack f (get_count conv ib)) i else begin
-        match fmt.[i] with
+        match Sformat.get fmt i with
         (* This is in fact an integer conversion (e.g. %ld, %ni, or %Lo). *)
         | 'd' | 'i' | 'o' | 'u' | 'x' | 'X' as conv ->
             let _x = scan_int_conv conv max ib in
             (* Look back to the character that triggered the integer conversion
                (this character is either 'l', 'n' or 'L'), to find the
                conversion to apply to the integer token read. *)
-            begin match fmt.[i - 1] with
+            begin match Sformat.get fmt (i - 1) with
             | 'l' -> scan_fmt (stack f (token_int32 conv ib)) (i + 1)
             | 'n' -> scan_fmt (stack f (token_nativeint conv ib)) (i + 1)
             | _ -> scan_fmt (stack f (token_int64 conv ib)) (i + 1) end
@@ -985,14 +1050,14 @@ let kscanf ib ef fmt f =
     | '0' .. '9' as conv ->
         let rec read_width accu i =
           if i > lim then accu, i else
-          match fmt.[i] with
+          match Sformat.get fmt i with
           | '0' .. '9' as c ->
              let accu = 10 * accu + int_value_of_char c in
              read_width accu (i + 1)
           | _ -> accu, i in
         let max, i = read_width (int_value_of_char conv) (i + 1) in
         if i > lim then incomplete_format fmt else begin
-        match fmt.[i] with
+        match Sformat.get fmt i with
         | '.' ->
           let p, i = read_width 0 (i + 1) in
           scan_conversion skip (max + p + 1) f i
@@ -1001,7 +1066,7 @@ let kscanf ib ef fmt f =
         let i = succ i in
         let j =
           Printf.sub_format incomplete_format bad_conversion conv fmt i + 1 in
-        let mf = String.sub fmt i (j - i - 2) in
+        let mf = Sformat.sub fmt i (j - i - 2) in
         let _x = scan_String max ib in
         let rf = token_string ib in
         if not (compatible_format_type mf rf)
@@ -1013,8 +1078,8 @@ let kscanf ib ef fmt f =
 
   and scan_fmt_stoppers i =
     if i > lim then i - 1, [] else
-    match fmt.[i] with
-    | '@' when i < lim -> let i = i + 1 in i, [fmt.[i]]
+    match Sformat.get fmt i with
+    | '@' when i < lim -> let i = i + 1 in i, [Sformat.get fmt i]
     | '@' when i = lim -> incomplete_format fmt
     | _ -> i - 1, [] in
 
@@ -1035,7 +1100,7 @@ let sscanf s = bscanf (Scanning.from_string s);;
 let scanf fmt = bscanf Scanning.stdib fmt;;
 
 let bscanf_format ib fmt f =
-  let fmt = format_to_string fmt in
+  let fmt = Sformat.unsafe_to_string fmt in
   let fmt1 = ignore (scan_String max_int ib); token_string ib in
   if not (compatible_format_type fmt1 fmt) then
     format_mismatch fmt1 fmt ib else
@@ -1044,4 +1109,4 @@ let bscanf_format ib fmt f =
 
 let sscanf_format s fmt f = bscanf_format (Scanning.from_string s) fmt f;;
 
-let scan_format s fmt = sscanf_format s fmt (fun x -> x);;
+let format_from_string s fmt = sscanf_format s fmt (fun x -> x);;
diff --git a/stdlib/scanf.mli b/stdlib/scanf.mli
index 646fcccdb..14cd949ed 100644
--- a/stdlib/scanf.mli
+++ b/stdlib/scanf.mli
@@ -269,7 +269,7 @@ val sscanf_format :
     (('a, 'b, 'c, 'd) format4 -> 'e) -> 'e;;
 (** Same as {!Scanf.bscanf}, but inputs from the given string. *)
 
-val scan_format :
+val format_from_string :
   string -> ('a, 'b, 'c, 'd) format4 -> ('a, 'b, 'c, 'd) format4;;
 (** Same as {!Scanf.sscanf_format}, but converts the given string to a format
   string. *)
diff --git a/stdlib/sys.ml b/stdlib/sys.ml
index ab8694733..7ed1a5071 100644
--- a/stdlib/sys.ml
+++ b/stdlib/sys.ml
@@ -78,4 +78,4 @@ let catch_break on =
 
 (* OCaml version string, must be in the format described in sys.mli. *)
 
-let ocaml_version = "3.10+dev5 (2006-04-05)";;
+let ocaml_version = "3.10+dev6 (2006-04-05)";;