# Module Stdlib.Buffer

    module Buffer: Buffer

    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 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.

    val contents : t -> string

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

    val to_bytes : t -> bytes

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

- Since 4.02

    val 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`.

    val 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`.

- Since 3.11.2
- 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`.

    val nth : t -> int -> char

Get the n-th character of the buffer.

- Raises `Invalid_argument` if index out of bounds

    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 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.

    val output_buffer : out_channel -> t -> unit

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

    val truncate : t -> int -> unit

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

- Since 4.05.0
- Raises `Invalid_argument` if `len < 0` or `len > length b`.

## 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`.

    val add_char : t -> char -> unit

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

    val add_utf_8_uchar : t -> Uchar.t -> unit

`add_utf_8_uchar b u` appends the UTF-8 encoding of `u` at the end of buffer `b`.

- Since 4.06.0

    val add_utf_16le_uchar : t -> Uchar.t -> unit

`add_utf_16le_uchar b u` appends the UTF-16LE encoding of `u` at the end of buffer `b`.

- Since 4.06.0

    val add_utf_16be_uchar : t -> Uchar.t -> unit

`add_utf_16be_uchar b u` appends the UTF-16BE encoding of `u` at the end of buffer `b`.

- Since 4.06.0

    val add_string : t -> string -> unit

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

    val add_bytes : t -> bytes -> unit

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

- Since 4.02

    val 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`.

    val 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`.

- Since 4.02
- Raises `Invalid_argument` if `ofs` and `len` do not designate a valid range of `s`.

    val 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.

    val 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.

    val 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.
  - `Invalid_argument` if `len < 0` or `len > Sys.max_string_length`.

## Buffers and Sequences

    val to_seq : t -> char Seq.t

Iterate on the buffer, in increasing order.

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

- Since 4.07

    val to_seqi : t -> (int * char) Seq.t

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

    val add_seq : t -> char Seq.t -> unit

Add chars to the buffer

- Since 4.07

    val of_seq : char Seq.t -> 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.

    val add_uint8 : t -> int -> unit

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

- Since 4.08

    val add_int8 : t -> int -> unit

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

- Since 4.08

    val 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

    val 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

    val 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

    val 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

    val 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

    val 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

    val 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

    val 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

    val 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

    val 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

    val 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

    val 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