Module Stdlib.Buffer

Extensible buffers.

This module implements buffers that automatically expand as necessary. It provides accumulative concatenation of strings in linear time (instead of quadratic time when strings are concatenated pairwise). For example:

let concat_strings ss =
  let b = Buffer.create 16 in
    List.iter (Buffer.add_string b) ss;
    Buffer.contents b

Unsynchronized accesses

Unsynchronized accesses to a buffer may lead to an invalid buffer state. Thus, concurrent accesses to a buffer must be synchronized (for instance with a Mutex.t).

type t;

The abstract type of buffers.

let create: int => t;

create n returns a fresh buffer, initially empty. The n parameter is the initial size of the internal byte sequence that holds the buffer contents. That byte sequence 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.

let contents: t => string;

Return a copy of the current contents of the buffer. The buffer itself is unchanged.

let to_bytes: t => bytes;

Return a copy of the current contents of the buffer. The buffer itself is unchanged.

  • since 4.02
let sub: t => int => int => string;

Buffer.sub b off len returns a copy of len bytes from the current contents of the buffer b, starting at offset off.

  • raises Invalid_argument

    if off and len do not designate a valid range of b.

let blit: t => int => bytes => int => int => unit;

Buffer.blit src srcoff dst dstoff len copies len characters from the current contents of the buffer src, starting at offset srcoff to dst, starting at character dstoff.

  • raises Invalid_argument

    if srcoff and len do not designate a valid range of src, or if dstoff and len do not designate a valid range of dst.

  • since 3.11.2
let nth: t => int => char;

Get the n-th character of the buffer.

  • raises Invalid_argument

    if index out of bounds

let length: t => int;

Return the number of characters currently contained in the buffer.

let clear: t => unit;

Empty the buffer.

let reset: t => unit;

Empty the buffer and deallocate the internal byte sequence holding the buffer contents, replacing it with the initial internal byte sequence of length n that was allocated by Buffer.create n. For long-lived buffers that may have grown a lot, reset allows faster reclamation of the space used by the buffer.

let output_buffer: out_channel => t => unit;

output_buffer oc b writes the current contents of buffer b on the output channel oc.

let truncate: t => int => unit;

truncate b len truncates the length of b to len Note: the internal byte sequence is not shortened.

  • raises Invalid_argument

    if len < 0 or len > length b.

  • since 4.05

Appending

Note: all add_* operations can raise Failure if the internal byte sequence of the buffer would need to grow beyond Sys.max_string_length.

let add_char: t => char => unit;

add_char b c appends the character c at the end of buffer b.

let add_string: t => string => unit;

add_string b s appends the string s at the end of buffer b.

let add_bytes: t => bytes => unit;

add_bytes b s appends the byte sequence s at the end of buffer b.

  • since 4.02
let add_substring: t => string => int => int => unit;

add_substring b s ofs len takes len characters from offset ofs in string s and appends them at the end of buffer b.

  • raises Invalid_argument

    if ofs and len do not designate a valid range of s.

let add_subbytes: t => bytes => int => int => unit;

add_subbytes b s ofs len takes len characters from offset ofs in byte sequence s and appends them at the end of buffer b.

  • raises Invalid_argument

    if ofs and len do not designate a valid range of s.

  • since 4.02
let add_substitute: t => (string => string) => string => unit;

add_substitute b f s appends the string pattern s at the end of buffer b with substitution. The substitution process looks for variables into the pattern and substitutes each variable name by its value, as obtained by applying the mapping f to the variable name. Inside the string pattern, a variable name immediately follows a non-escaped $ character and is one of the following:

  • a non empty sequence of alphanumeric or _ characters,
  • an arbitrary sequence of characters enclosed by a pair of matching parentheses or curly brackets. An escaped $ character is a $ that immediately follows a backslash character; it then stands for a plain $.
  • raises Not_found

    if the closing character of a parenthesized variable cannot be found.

let add_buffer: t => t => unit;

add_buffer b1 b2 appends the current contents of buffer b2 at the end of buffer b1. b2 is not modified.

let add_channel: t => in_channel => int => unit;

add_channel b ic n reads at most n characters from the input channel ic and stores them at the end of buffer b.

  • raises End_of_file

    if the channel contains fewer than n characters. In this case, the characters are still added to the buffer, so as to avoid loss of data.

  • raises Invalid_argument

    if len < 0 or len > Sys.max_string_length.

Buffers and Sequences

let to_seq: t => Seq.t(char);

Iterate on the buffer, in increasing order.

The behavior is not specified if the buffer is modified during iteration.

  • since 4.07
let to_seqi: t => Seq.t((int, char));

Iterate on the buffer, in increasing order, yielding indices along chars.

The behavior is not specified if the buffer is modified during iteration.

  • since 4.07
let add_seq: t => Seq.t(char) => unit;

Add chars to the buffer

  • since 4.07
let of_seq: Seq.t(char) => t;

Create a buffer from the generator

  • since 4.07

Binary encoding of integers

The functions in this section append binary encodings of integers to buffers.

Little-endian (resp. big-endian) encoding means that least (resp. most) significant bytes are stored first. Big-endian is also known as network byte order. Native-endian encoding is either little-endian or big-endian depending on Sys.big_endian.

32-bit and 64-bit integers are represented by the int32 and int64 types, which can be interpreted either as signed or unsigned numbers.

8-bit and 16-bit integers are represented by the int type, which has more bits than the binary encoding. Functions that encode these values truncate their inputs to their least significant bytes.

let add_uint8: t => int => unit;

add_uint8 b i appends a binary unsigned 8-bit integer i to b.

  • since 4.08
let add_int8: t => int => unit;

add_int8 b i appends a binary signed 8-bit integer i to b.

  • since 4.08
let add_uint16_ne: t => int => unit;

add_uint16_ne b i appends a binary native-endian unsigned 16-bit integer i to b.

  • since 4.08
let add_uint16_be: t => int => unit;

add_uint16_be b i appends a binary big-endian unsigned 16-bit integer i to b.

  • since 4.08
let add_uint16_le: t => int => unit;

add_uint16_le b i appends a binary little-endian unsigned 16-bit integer i to b.

  • since 4.08
let add_int16_ne: t => int => unit;

add_int16_ne b i appends a binary native-endian signed 16-bit integer i to b.

  • since 4.08
let add_int16_be: t => int => unit;

add_int16_be b i appends a binary big-endian signed 16-bit integer i to b.

  • since 4.08
let add_int16_le: t => int => unit;

add_int16_le b i appends a binary little-endian signed 16-bit integer i to b.

  • since 4.08
let add_int32_ne: t => int32 => unit;

add_int32_ne b i appends a binary native-endian 32-bit integer i to b.

  • since 4.08
let add_int32_be: t => int32 => unit;

add_int32_be b i appends a binary big-endian 32-bit integer i to b.

  • since 4.08
let add_int32_le: t => int32 => unit;

add_int32_le b i appends a binary little-endian 32-bit integer i to b.

  • since 4.08
let add_int64_ne: t => int64 => unit;

add_int64_ne b i appends a binary native-endian 64-bit integer i to b.

  • since 4.08
let add_int64_be: t => int64 => unit;

add_int64_be b i appends a binary big-endian 64-bit integer i to b.

  • since 4.08
let add_int64_le: t => int64 => unit;

add_int64_ne b i appends a binary little-endian 64-bit integer i to b.

  • since 4.08