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.
type t = Caml.out_channel
include sig ... end
val sexp_of_t : t -> Stdio__.Import.Ppx_sexp_conv_lib.Sexp.t
val stdout : t
val stderr : t
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
EIO -- I don't recall seeing this. I think it's rare.
See "man 2 close" for details.
Outputs a list of lines, each terminated by a newline character
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
t as argument and must print to it instead of returning a string.
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.
print_endline str outputs
stdout followed by a newline then flushes
prerr_endline str outputs
stderr followed by a newline then flushes
The first argument of these is the file name to write to.