## `io`: buffered input and output

    type in_channel
    type out_channel

  The abstract types of input channels and output channels.

    exception End_of_file

  Raised when an operation cannot complete, because the end of the file has been reached.

    value stdin : in_channel
    value std_in : in_channel
    value stdout : out_channel
    value std_out : out_channel
    value stderr : out_channel
    value std_err : out_channel

  The standard input, standard output, and standard error output for the process. `std_in`, `std_out` and `std_err` are respectively synonymous with `stdin`, `stdout` and `stderr`.

    value exit : int -> 'a

  Flush all pending writes on `std_out` and `std_err`, and terminate the process, returning the given status code to the operating system (usually 0 to indicate no errors, and a small positive integer to indicate failure.) This function should be called at the end of all standalone programs that output results on `std_out` or `std_err`; otherwise, the program may appear to produce no output, or its output may be truncated.

### Output functions on standard output

    value print_char : char -> unit

  Print the character on standard output.

    value print_string : string -> unit

  Print the string on standard output.

    value print_int : int -> unit

  Print the integer, in decimal, on standard output.

    value print_float : float -> unit

  Print the floating-point number, in decimal, on standard output.

    value print_endline : string -> unit

  Print the string, followed by a newline character, on standard output.

    value print_newline : unit -> unit

  Print a newline character on standard output, and flush standard output. This can be used to simulate line buffering of standard output.

### Output functions on standard error

    value prerr_char : char -> unit

  Print the character on standard error.

    value prerr_string : string -> unit

  Print the string on standard error.

    value prerr_int : int -> unit

  Print the integer, in decimal, on standard error.

    value prerr_float : float -> unit

  Print the floating-point number, in decimal, on standard error.

    value prerr_endline : string -> unit

  Print the string, followed by a newline character on standard error and flush standard error.

### Input functions on standard input

    value read_line : unit -> string

  Flush standard output, then read characters from standard input until a newline character is encountered. Return the string of all characters read, without the newline character at the end.

    value read_int : unit -> int

  Flush standard output, then read one line from standard input and convert it to an integer. Raise `Failure "int_of_string"` if the line read is not a valid representation of an integer.

    value read_float : unit -> float

  Flush standard output, then read one line from standard input and convert it to a floating-point number. The result is unspecified if the line read is not a valid representation of a floating-point number.

### General output functions

    value open_out : string -> out_channel

  Open the named file for writing, and return a new output channel on that file, positionned at the beginning of the file. The file is truncated to zero length if it already exists. It is created if it does not already exists. Raise `sys__Sys_error` if the file could not be opened.

    value open_out_bin : string -> out_channel

  Same as `open_out`, but the file is opened in binary mode, so that no translation takes place during writes. On operating systems that do not distinguish between text mode and binary mode, this function behaves like `open_out`.

    value open_out_gen : sys__open_flag list -> int -> string -> out_channel

  `open_out_gen mode rights filename` opens the file named `filename` for writing, as above. The extra argument `mode` specify the opening mode (see `sys__open`). The extra argument `rights` specifies the file permissions, in case the file must be created (see `sys__open`). `open_out` and `open_out_bin` are special cases of this function.

    value open_descriptor_out : int -> out_channel

  `open_descriptor_out fd` returns a buffered output channel writing to the file descriptor `fd`. The file descriptor `fd` must have been previously opened for writing, else the behavior is undefined.

    value flush : out_channel -> unit

  Flush the buffer associated with the given output channel, performing all pending writes on that channel. Interactive programs must be careful about flushing `std_out` and `std_err` at the right time.

    value output_char : out_channel -> char -> unit

  Write the character on the given output channel.

    value output_string : out_channel -> string -> unit

  Write the string on the given output channel.

    value output : out_channel -> string -> int -> int -> unit

  `output chan buff ofs len` writes `len` characters from string `buff`, starting at offset `ofs`, to the output channel `chan`. Raise `Invalid_argument "output"` if `ofs` and `len` do not designate a valid substring of `buff`.

    value output_byte : out_channel -> int -> unit

  Write one 8-bit integer (as the single character with that code) on the given output channel. The given integer is taken modulo 256.

    value output_binary_int : out_channel -> int -> unit

  Write one integer in binary format on the given output channel. The only reliable way to read it back is through the `input_binary_int` function. The format is compatible across all machines for a given version of Caml Light.

    value output_value : out_channel -> 'a -> unit

  Write the representation of a structured value of any type to a channel. Circularities and sharing inside the value are detected and preserved. The object can be read back, by the function `input_value`. The format is compatible across all machines for a given version of Caml Light.

    value output_compact_value : out_channel -> 'a -> unit

  Same as `output_value`, but uses a different format, which occupies less space on the file, but takes more time to generate and read back.

    value seek_out : out_channel -> int -> unit

  `seek_out chan pos` sets the current writing position to `pos` for channel `chan`. This works only for regular files. On files of other kinds (such as terminals, pipes and sockets), the behavior is unspecified.

    value pos_out : out_channel -> int

  Return the current writing position for the given channel.

    value out_channel_length : out_channel -> int

  Return the total length (number of characters) of the given channel. This works only for regular files. On files of other kinds, the result is meaningless.

    value close_out : out_channel -> unit

  Close the given channel, flushing all buffered write operations. The behavior is unspecified if any of the functions above is called on a closed channel.

### General input functions

    value open_in : string -> in_channel

  Open the named file for reading, and return a new input channel on that file, positionned at the beginning of the file. Raise `sys__Sys_error` if the file could not be opened.

    value open_in_bin : string -> in_channel

  Same as `open_in`, but the file is opened in binary mode, so that no translation takes place during reads. On operating systems that do not distinguish between text mode and binary mode, this function behaves like `open_in`.

    value open_in_gen : sys__open_flag list -> int -> string -> in_channel

  `open_in_gen mode rights filename` opens the file named `filename` for reading, as above. The extra arguments `mode` and `rights` specify the opening mode and file permissions (see `sys__open`). `open_in` and `open_in_bin` are special cases of this function.

    value open_descriptor_in : int -> in_channel

  `open_descriptor_in fd` returns a buffered input channel reading from the file descriptor `fd`. The file descriptor `fd` must have been previously opened for reading, else the behavior is undefined.

    value input_char : in_channel -> char

  Read one character from the given input channel. Raise `End_of_file` if there are no more characters to read.

    value input_line : in_channel -> string

  Read characters from the given input channel, until a newline character is encountered. Return the string of all characters read, without the newline character at the end. Raise `End_of_file` if the end of the file is reached at the beginning of line.

    value input : in_channel -> string -> int -> int -> int

  `input chan buff ofs len` attempts to read `len` characters from channel `chan`, storing them in string `buff`, starting at character number `ofs`. 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. A return value between 0 and `len` exclusive means that no more characters were available at that time; `input` must be called again to read the remaining characters, if desired. Exception `Invalid_argument "input"` is raised if `ofs` and `len` do not designate a valid substring of `buff`.

    value really_input : in_channel -> string -> int -> int -> unit

  `really_input chan buff ofs len` reads `len` characters from channel `chan`, storing them in string `buff`, starting at character number `ofs`. Raise `End_of_file` if the end of file is reached before `len` characters have been read. Raise `Invalid_argument "really_input"` if `ofs` and `len` do not designate a valid substring of `buff`.

    value input_byte : in_channel -> int

  Same as `input_char`, but return the 8-bit integer representing the character. Raise `End_of_file` if an end of file was reached.

    value input_binary_int : in_channel -> int

  Read an integer encoded in binary format from the given input channel. See `output_binary_int`. Raise `End_of_file` if an end of file was reached while reading the integer.

    value input_value : in_channel -> 'a

  Read the representation of a structured value, as produced by `output_value` or `output_compact_value`, and return the corresponding value. This is not type-safe. The type of the returned object is not `'a` properly speaking: the returned object has one unique type, which cannot be determined at compile-time. The programmer should explicitly give the expected type of the returned value, using the following syntax: `(input_value chan : type)`. The behavior is unspecified if the object in the file does not belong to the given type.

    value seek_in : in_channel -> int -> unit

  `seek_in 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.

    value pos_in : in_channel -> int

  Return the current reading position for the given channel.

    value in_channel_length : in_channel -> int

  Return the total length (number of characters) of the given channel. This works only for regular files. On files of other kinds, the result is meaningless.

    value close_in : in_channel -> unit

  Close the given channel. Anything can happen if any of the functions above is called on a closed channel.