19.3 Module Buffer: extensible string buffers

This module implements string buffers that automatically expand as necessary. It provides accumulative concatenation of strings in quasi-linear time (instead of quadratic time when strings are concatenated pairwise).
type t
The abstract type of buffers.
val create : int -> t
create n returns a fresh buffer, initially empty. The n parameter is the initial size of the internal string that holds the buffer contents. That string is automatically reallocated when more than n characters are stored in the buffer, but shrinks back to n characters when reset is called. For best performance, n should be of the same order of magnitude as the number of characters that are expected to be stored in the buffer (for instance, 80 for a buffer that holds one output line). Nothing bad will happen if the buffer grows beyond that limit, however. In doubt, take n = 16 for instance. If n is not between 1 and Sys.max_string_length, it will be clipped to that interval.
val contents : t -> string
Return a copy of the current contents of the buffer. The buffer itself is unchanged.
val length : t -> int
Return the number of characters currently contained in the buffer.
val clear : t -> unit
Empty the buffer.
val reset : t -> unit
Empty the buffer and deallocate the internal string holding the buffer contents, replacing it with the initial internal string of length n that was allocated by create n. For long-lived buffers that may have grown a lot, reset allows faster reclaimation of the space used by the buffer.
val add_char : t -> char -> unit
add_char b c appends the character c at the end of the buffer b.
val add_string : t -> string -> unit
add_string b s appends the string s at the end of the buffer b.
val add_substring : t -> string -> pos:int -> len:int -> unit
add_substring b s ofs len takes len characters from offset ofs in string s and appends them at the end of the buffer b.
val add_buffer : t -> src:t -> unit
add_buffer b1 b2 appends the current contents of buffer b2 at the end of buffer b1. b2 is not modified.
val add_channel : t -> in_channel -> len:int -> unit
add_channel b ic n reads exactly n character from the input channel ic and stores them at the end of buffer b. Raise End_of_file if the channel contains fewer than n characters.
val output_buffer : out_channel -> t -> unit
output_buffer oc b writes the current contents of buffer b on the output channel oc.