Module Stdlib.In_channel

Input channels.

This module provides functions for working with input channels.

See the example section below.

Channels

type t = in_channel;

The type of input channel.

type open_flag = open_flag =
  1. | Open_rdonly
    /*

    open for reading.

    */
  2. | Open_wronly
    /*

    open for writing.

    */
  3. | Open_append
    /*

    open for appending: always write at end of file.

    */
  4. | Open_creat
    /*

    create the file if it does not exist.

    */
  5. | Open_trunc
    /*

    empty the file if it already exists.

    */
  6. | Open_excl
    /*

    fail if Open_creat and the file already exists.

    */
  7. | Open_binary
    /*

    open in binary mode (no conversion).

    */
  8. | Open_text
    /*

    open in text mode (may perform conversions).

    */
  9. | Open_nonblock
    /*

    open in non-blocking mode.

    */
;

Opening modes for open_gen.

let stdin: t;

The standard input for the process.

let open_bin: string => t;

Open the named file for reading, and return a new input channel on that file, positioned at the beginning of the file.

let open_text: string => t;

Same as open_bin, but the file is opened in text mode, so that newline translation takes place during reads. On operating systems that do not distinguish between text mode and binary mode, this function behaves like open_bin.

let open_gen: list(open_flag) => int => string => t;

open_gen mode perm filename opens the named file for reading, as described above. The extra arguments mode and perm specify the opening mode and file permissions. open_text and open_bin are special cases of this function.

let with_open_bin: string => (t => 'a) => 'a;

with_open_bin fn f opens a channel ic on file fn and returns f ic. After f returns, either with a value or by raising an exception, ic is guaranteed to be closed.

let with_open_text: string => (t => 'a) => 'a;

Like with_open_bin, but the channel is opened in text mode (see open_text).

let with_open_gen: list(open_flag) => int => string => (t => 'a) => 'a;

Like with_open_bin, but can specify the opening mode and file permission, in case the file must be created (see open_gen).

let close: t => unit;

Close the given channel. Input functions raise a Sys_error exception when they are applied to a closed input channel, except close, which does nothing when applied to an already closed channel.

let close_noerr: t => unit;

Same as close, but ignore all errors.

Input

let input_char: t => option(char);

Read one character from the given input channel. Returns None if there are no more characters to read.

let input_byte: t => option(int);

Same as input_char, but return the 8-bit integer representing the character. Returns None if the end of file was reached.

let input_line: t => option(string);

input_line ic reads characters from ic until a newline or the end of file is reached. Returns the string of all characters read, without the newline (if any). Returns None if the end of the file has been reached. In particular, this will be the case if the last line of input is empty.

A newline is the character \n unless the file is open in text mode and Sys.win32 is true in which case it is the sequence of characters \r\n.

let really_input_string: t => int => option(string);

really_input_string ic len reads len characters from channel ic and returns them in a new string. Returns None if the end of file is reached before len characters have been read.

If the same channel is read concurrently by multiple threads, the returned string is not guaranteed to contain contiguous characters from the input.

let input_all: t => string;

input_all ic reads all remaining data from ic.

If the same channel is read concurrently by multiple threads, the returned string is not guaranteed to contain contiguous characters from the input.

let input_lines: t => list(string);

input_lines ic reads lines using input_line until the end of file is reached. It returns the list of all lines read, in the order they were read. The newline characters that terminate lines are not included in the returned strings. Empty lines produce empty strings.

  • since 5.1

Advanced input

let input: t => bytes => int => int => int;

input ic buf pos len reads up to len characters from the given channel ic, storing them in byte sequence buf, starting at character number pos. It returns the actual number of characters read, between 0 and len (inclusive). A return value of 0 means that the end of file was reached.

Use really_input to read exactly len characters.

let really_input: t => bytes => int => int => option(unit);

really_input ic buf pos len reads len characters from channel ic, storing them in byte sequence buf, starting at character number pos.

Returns None if the end of file is reached before len characters have been read.

If the same channel is read concurrently by multiple threads, the bytes read by really_input are not guaranteed to be contiguous.

let fold_lines: ('acc => string => 'acc) => 'acc => t => 'acc;

fold_lines f init ic reads lines from ic using input_line until the end of file is reached, and successively passes each line to function f in the style of a fold. More precisely, if lines l1, ..., lN are read, fold_lines f init ic computes f (... (f (f init l1) l2) ...) lN. If f has no side effects, this is equivalent to List.fold_left f init (In_channel.input_lines ic), but is more efficient since it does not construct the list of all lines read.

  • since 5.1

Seeking

let seek: t => int64 => unit;

seek chan pos sets the current reading position to pos for channel chan. This works only for regular files. On files of other kinds, the behavior is unspecified.

let pos: t => int64;

Return the current reading position for the given channel. For files opened in text mode under Windows, the returned position is approximate (owing to end-of-line conversion); in particular, saving the current position with pos, then going back to this position using seek will not work. For this programming idiom to work reliably and portably, the file must be opened in binary mode.

Attributes

let length: t => int64;

Return the size (number of characters) of the regular file on which the given channel is opened. If the channel is opened on a file that is not a regular file, the result is meaningless. The returned size does not take into account the end-of-line translations that can be performed when reading from a channel opened in text mode.

let set_binary_mode: t => bool => unit;

set_binary_mode ic true sets the channel ic to binary mode: no translations take place during input.

set_binary_mode ic false sets the channel ic to text mode: depending on the operating system, some translations may take place during input. For instance, under Windows, end-of-lines will be translated from \r\n to \n.

This function has no effect under operating systems that do not distinguish between text mode and binary mode.

let is_binary_mode: t => bool;

is_binary_mode ic returns whether the channel ic is in binary mode (see set_binary_mode).

  • since 5.2
let isatty: t => bool;

isatty ic is true if ic refers to a terminal or console window, false otherwise.

  • since 5.1

Examples

Reading the contents of a file:

let read_file file = In_channel.with_open_bin file In_channel.input_all

Reading a line from stdin:

let user_input () = In_channel.input_line In_channel.stdin