added Buffer.sub & Buffer.nth

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@6203 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02

stdlib/buffer.ml

@@ -27,6 +27,22 @@ let create n =
 
 let contents b = String.sub b.buffer 0 b.position
 
+let sub b ofs len =
+  if ofs < 0 || len < 0 || ofs > b.position - len 
+  then invalid_arg "Buffer.sub"
+  else begin
+    let r = String.create len in
+    String.blit b.buffer ofs r 0 len;
+    r
+  end
+;;
+
+let nth b ofs = 
+  if ofs < 0 || ofs >= b.position then 
+   invalid_arg "Buffer.nth"
+  else String.get b.buffer ofs
+;;
+
 let length b = b.position
 
 let clear b = b.position <- 0

stdlib/buffer.mli

@@ -40,6 +40,16 @@ val contents : t -> string
 (** Return a copy of the current contents of the buffer.
    The buffer itself is unchanged. *)
 
+val sub : t -> int -> int -> string
+(** [Buffer.sub b off len] returns (a copy of) the substring of the
+current contents of the buffer [b] starting at offset [off] of length
+[len] bytes. May raise {!Invalid_arg} if out of bounds request. The
+buffer itself is unaffected. *)
+
+val nth : t -> int -> char
+(** get the n-th character of the buffer. Raise {!Invalid_arg} if
+index out of bounds *)
+
 val length : t -> int
 (** Return the number of characters currently contained in the buffer. *)