Module Buffer

module Buffer: sig .. end

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
  • Alert unsynchronized_access. Unsynchronized accesses to buffers are a programming error.

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.

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