Module Stdio.Out_channel

An output channel for doing blocking writes to destinations like files and sockets.

Note that an Out_channel.t is a custom block with a finalizer, and so is allocated directly to the major heap. Creating a lot of out_channels can result in many major collections and poor performance.

Note that this is simply another interface on the out_channel type in the OCaml standard library.

As for the output functions in the standard library, all the functions in this module, unless otherwise specified, can raise Sys_error when the system calls they invoke fail.

type t = Caml.out_channel
val sexp_of_t : t -> Base.Sexp.t
include Base.Equal.S with type t := t
type t
val equal : t Base.Equal.equal
val stdout : t
val stderr : t
type 'a with_create_args = ?⁠binary:Base.bool -> ?⁠append:Base.bool -> ?⁠fail_if_exists:Base.bool -> ?⁠ -> 'a
val create : (Base.string -> t) with_create_args
val with_file : (Base.string -> f:(t -> 'a) -> 'a) with_create_args
val close : t -> Base.unit

close t flushes and closes t, and may raise an exception. close returns () and does not raise if t is already closed. close raises an exception if the close() system call on the underlying file descriptor fails (i.e. returns -1), which would happen in the following cases:

EBADF -- this would happen if someone else did close() system call on the underlying fd, which I would think a rare event.

EINTR -- would happen if the system call was interrupted by a signal, which would be rare. Also, I think we should probably just catch EINTR and re-attempt the close. Unfortunately, we can't do that in OCaml because the OCaml library marks the out_channel as closed even if the close syscall fails, so a subsequent call close_out_channel will be a no-op. This should really be fixed in the OCaml library C code, having it restart the close() syscall on EINTR. I put a couple CRs in fixed_close_channel, our rework of OCaml's caml_ml_close_channel,

EIO -- I don't recall seeing this. I think it's rare.

See "man 2 close" for details.

val close_no_err : t -> Base.unit

close_no_err tries to flush and close t. It does not raise.

val set_binary_mode : t -> Base.bool -> Base.unit
val flush : t -> Base.unit
val output : t -> buf:Base.bytes -> -> -> Base.unit
val output_string : t -> Base.string -> Base.unit
val output_substring : t -> buf:Base.string -> -> -> Base.unit
val output_bytes : t -> Base.Bytes.t -> Base.unit
val output_char : t -> Base.char -> Base.unit
val output_byte : t -> -> Base.unit
val output_binary_int : t -> -> Base.unit
val output_buffer : t -> Base.Buffer.t -> Base.unit
val output_value : t -> _ -> Base.unit

OCaml's internal Marshal format

val newline : t -> Base.unit
val output_lines : t -> Base.string Base.list -> Base.unit

Outputs a list of lines, each terminated by a newline character

val fprintf : t -> ('atBase.unit) Base.format -> 'a

Formatted printing to an out channel. This is the same as Printf.sprintf except that it outputs to t instead of returning a string. Similarly, the function arguments corresponding to conversions specifications such as %a or %t takes t as argument and must print to it instead of returning a string.

val printf : ('atBase.unit) Base.format -> 'a

printf fmt is the same as fprintf stdout fmt

val print_s : ?⁠mach:Base.unit -> Base.Sexp.t -> Base.unit

print_s sexp outputs sexp on stdout, by default using Sexp.to_string_hum, or, with ~mach:(), Sexp.to_string_mach.

val eprint_s : ?⁠mach:Base.unit -> Base.Sexp.t -> Base.unit

eprint_s sexp outputs sexp on stderr, by default using Sexp.to_string_hum, or, with ~mach:(), Sexp.to_string_mach.

val eprintf : ('atBase.unit) Base.format -> 'a

eprintf fmt is the same as fprintf stderr fmt

val kfprintf : (t -> 'a) -> t -> ('btBase.unit'a) Base.format4 -> 'b

kfprintf k t fmt is the same as fprintf t fmt, but instead of returning immediately, passes the out channel to k at the end of printing.

val print_string : Base.string -> Base.unit

print_string s = output_string stdout s

val print_endline : Base.string -> Base.unit

print_endline str outputs str to stdout followed by a newline then flushes stdout

val prerr_endline : Base.string -> Base.unit

prerr_endline str outputs str to stderr followed by a newline then flushes stderr

val seek : t -> Base.int64 -> Base.unit
val pos : t -> Base.int64
val length : t -> Base.int64
val write_lines : Base.string -> Base.string Base.list -> Base.unit

The first argument of these is the file name to write to.

val write_all : Base.string -> data:Base.string -> Base.unit