# Module IO

    module IO: sig .. end

High-order abstract I/O.

IO module simply deals with abstract inputs/outputs. It provides a set of methods for working with these IO as well as several constructors that enable to write to an underlying channel, buffer, or enum.

    type input

The abstract input type.

    type 'a output

The abstract output type, `'a` is the accumulator data, it is returned when the `close_out` function is called.

    exception No_more_input

This exception is raised when reading on an input with the `read` or `nread` functions while there is no available token to read.

    exception Input_closed

This exception is raised when reading on a closed input.

    exception Output_closed

This exception is raised when reading on a closed output.

Standard API

    val read : input -> char

Read a single char from an input or raise `No_more_input` if no input available.

    val nread : input -> int -> ExtBytes.Bytes.t

`nread i n` reads a byte sequence of size up to `n` from an input. The function will raise `No_more_input` if no input is available. It will raise `Invalid_argument` if `n` < 0.

    val really_nread : input -> int -> ExtBytes.Bytes.t

`really_nread i n` reads a byte sequence of exactly `n` characters from the input. Raises `No_more_input` if at least `n` characters are not available. Raises `Invalid_argument` if `n` < 0.

    val nread_string : input -> int -> string

as `nread`, but reads a string.

    val really_nread_string : input -> int -> string

as `really_nread`, but reads a string.

    val input : input -> ExtBytes.Bytes.t -> int -> int -> int

`input i b p l` reads up to `l` characters from the given input, storing them in buffer `b`, starting at character number `p`. It returns the actual number of characters read or raise `No_more_input` if no character can be read. It will raise `Invalid_argument` if `p` and `l` do not designate a valid subsequence of `b`.

    val really_input : input -> ExtBytes.Bytes.t -> int -> int -> int

`really_input i b p l` reads exactly `l` characters from the given input, storing them in the buffer `b`, starting at position `p`. For consistency with `IO.input` it returns `l`. Raises `No_more_input` if at `l` characters are not available. Raises `Invalid_argument` if `p` and `l` do not designate a valid subsequence of `b`.

    val close_in : input -> unit

Close the input. It can no longer be read from.

    val write : 'a output -> char -> unit

Write a single char to an output.

    val nwrite : 'a output -> ExtBytes.Bytes.t -> unit

Write a byte sequence to an output.

    val nwrite_string : 'a output -> string -> unit

Write a string to an output.

    val output : 'a output -> ExtBytes.Bytes.t -> int -> int -> int

`output o b p l` writes up to `l` characters from byte sequence `b`, starting at offset `p`. It returns the number of characters written. It will raise `Invalid_argument` if `p` and `l` do not designate a valid subsequence of `b`.

    val really_output : 'a output -> ExtBytes.Bytes.t -> int -> int -> int

`really_output o b p l` writes exactly `l` characters from byte sequence `b` onto the the output, starting with the character at offset `p`. For consistency with `IO.output` it returns `l`. Raises `Invalid_argument` if `p` and `l` do not designate a valid subsequence of `b`.

    val flush : 'a output -> unit

Flush an output.

    val close_out : 'a output -> 'a

Close the output and return its accumulator data. It can no longer be written.

Creation of IO Inputs/Outputs

    val input_string : string -> input

Create an input that will read from a string.

    val input_bytes : ExtBytes.Bytes.t -> input

Create an input that will read from a byte sequence.

    val output_string : unit -> string output

Create an output that will write into a string in an efficient way. When closed, the output returns all the data written into it.

    val output_bytes : unit -> ExtBytes.Bytes.t output

Create an output that will write into a byte sequence in an efficient way. When closed, the output returns all the data written into it.

    val output_strings : unit -> string list output

Create an output that will write into a string in an efficient way. When closed, the output returns all the data written into it. Several strings are used in case the output size excess max_string_length

    val input_channel : Stdlib.in_channel -> input

Create an input that will read from a channel.

    val output_channel : Stdlib.out_channel -> unit output

Create an output that will write into a channel.

    val input_enum : char Enum.t -> input

Create an input that will read from an `enum`.

    val output_enum : unit -> char Enum.t output

Create an output that will write into an `enum`. The final enum is returned when the output is closed.

    val create_in : read:(unit -> char) ->
           input:(ExtBytes.Bytes.t -> int -> int -> int) ->
           close:(unit -> unit) -> input

Fully create an input by giving all the needed functions.

    val create_out : write:(char -> unit) ->
           output:(ExtBytes.Bytes.t -> int -> int -> int) ->
           flush:(unit -> unit) -> close:(unit -> 'a) -> 'a output

Fully create an output by giving all the needed functions.

Utilities

    val scanf : input -> ('a, 'b, 'c, 'd) Stdlib.Scanf.scanner

The scanf function works for any input.

    val printf : 'a output -> ('b, unit, string, unit) Stdlib.format4 -> 'b

The printf function works for any output.

    val read_all : input -> string

read all the contents of the input until `No_more_input` is raised.

    val pipe : unit -> input * unit output

Create a pipe between an input and an ouput. Data written from the output can be read from the input.

    val pos_in : input -> input * (unit -> int)

Create an input that provide a count function of the number of Bytes.t read from it.

    val pos_out : 'a output -> 'a output * (unit -> int)

Create an output that provide a count function of the number of Bytes.t written through it.

    val cast_output : 'a output -> unit output

You can safely transform any output to an unit output in a safe way by using this function.

Binary files API

Here is some API useful for working with binary files, in particular binary files generated by C applications. By default, encoding of multibyte integers is low-endian. The BigEndian module provide multibyte operations with other encoding.

    exception Overflow of string

Exception raised when a read or write operation cannot be completed.

    val read_byte : input -> int

Read an unsigned 8-bit integer.

    val read_signed_byte : input -> int

Read an signed 8-bit integer.

    val read_ui16 : input -> int

Read an unsigned 16-bit word.

    val read_i16 : input -> int

Read a signed 16-bit word.

    val read_i31 : input -> int

Read a signed 32-bit integer. Raise `Overflow` if the read integer cannot be represented as an OCaml 31-bit integer.

    val read_i32 : input -> int

Deprecated, same as read_i31

    val read_i32_as_int : input -> int

Read a signed 32-bit integer, represented as OCaml integer, wrapping around 31-bit int on 32-bit architecture

    val read_real_i32 : input -> int32

Read a signed 32-bit integer as an OCaml int32.

    val read_i64 : input -> int64

Read a signed 64-bit integer as an OCaml int64.

    val read_float32 : input -> float

Read an IEEE single precision floating point value (32 bits).

    val read_double : input -> float

Read an IEEE double precision floating point value (64 bits).

    val read_string : input -> string

Read a null-terminated string.

    val read_bytes : input -> ExtBytes.Bytes.t

Read a null-terminated byte sequence.

    val read_line : input -> string

Read a LF or CRLF terminated string.

    val write_byte : 'a output -> int -> unit

Write an unsigned 8-bit byte.

    val write_ui16 : 'a output -> int -> unit

Write an unsigned 16-bit word.

    val write_i16 : 'a output -> int -> unit

Write a signed 16-bit word.

    val write_i31 : 'a output -> int -> unit

Write a signed 31-bit integer as 4 bytes.

    val write_i32 : 'a output -> int -> unit

Write a signed 32-bit integer.

    val write_real_i32 : 'a output -> int32 -> unit

Write an OCaml int32.

    val write_i64 : 'a output -> int64 -> unit

Write an OCaml int64.

    val write_float32 : 'a output -> float -> unit

Write an IEEE single precision floating point value (32 bits).

    val write_double : 'a output -> float -> unit

Write an IEEE double precision floating point value (64 bits).

    val write_string : 'a output -> string -> unit

Write a string and append an null character.

    val write_bytes : 'a output -> ExtBytes.Bytes.t -> unit

Write a byte sequence and append an null character.

    val write_line : 'a output -> string -> unit

Write a line and append a LF (it might be converted to CRLF on some systems depending on the underlying IO).

    module BigEndian: sig .. end

Same as operations above, but use big-endian encoding

Bits API

This enable you to read and write from an IO bit-by-bit or several bits at the same time.

    type in_bits

    type out_bits

    exception Bits_error

    val input_bits : input -> in_bits

Read bits from an input

    val output_bits : 'a output -> out_bits

Write bits to an output

    val read_bits : in_bits -> int -> int

Read up to 31 bits, raise Bits_error if n < 0 or n > 31

    val write_bits : out_bits -> nbits:int -> int -> unit

Write up to 31 bits represented as a value, raise Bits_error if nbits < 0 or nbits > 31 or the value representation excess nbits.

    val flush_bits : out_bits -> unit

Flush remaining unwritten bits, adding up to 7 bits which values 0.

    val drop_bits : in_bits -> unit

Drop up to 7 buffered bits and restart to next input character.

Generic IO Object Wrappers

Theses OO Wrappers have been written to provide easy support of ExtLib IO by external librairies. If you want your library to support ExtLib IO without actually requiring ExtLib to compile, you can should implement the classes `in_channel`, `out_channel`, `poly_in_channel` and/or `poly_out_channel` which are the common IO specifications established for ExtLib, OCamlNet and Camomile.

(see http://www.ocaml-programming.de/tmp/IO-Classes.html for more details).

    class in_channel : input -> object .. end

    class out_channel : 'a output -> object .. end

    class in_chars : input -> object .. end

    class out_chars : 'a output -> object .. end

    val from_in_channel : #in_channel -> input

    val from_out_channel : #out_channel -> unit output

    val from_in_chars : #in_chars -> input

    val from_out_chars : #out_chars -> unit output