Module Out_channel
: (moduleStdlib__Out_channel)Channelstypet = out_channel
The type of output channel.
typeopen_flag = open_flag =
| Open_rdonly (* open for reading.
*)
| Open_wronly (* open for writing.
*)
| Open_append (* open for appending: always write at end of file.
*)
| Open_creat (* create the file if it does not exist.
*)
| Open_trunc (* empty the file if it already exists.
*)
| Open_excl (* fail if Open_creat and the file already exists.
*)
| Open_binary (* open in binary mode (no conversion).
*)
| Open_text (* open in text mode (may perform conversions).
*)
| Open_nonblock (* open in non-blocking mode.
*)
Opening modes for Out_channel.open_gen .
valstdout : t
The standard output for the process.
valstderr : t
The standard error output for the process.
valopen_bin : string->t
Open the named file for writing, and return a new output channel on that file, positioned 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.
valopen_text : string->t
Same as Out_channel.open_bin , but the file is opened in text mode, so that newline translation takes
place during writes. On operating systems that do not distinguish between text mode and binary mode, this
function behaves like Out_channel.open_bin .
valopen_gen : open_flaglist->int->string->topen_genmodepermfilename opens the named file for writing, as described above. The extra argument mode
specifies the opening mode. The extra argument perm specifies the file permissions, in case the file must
be created. Out_channel.open_text and Out_channel.open_bin are special cases of this function.
valwith_open_bin : string->(t->'a)->'awith_open_binfnf opens a channel oc on file fn and returns foc . After f returns, either with a value or by raising an exception, oc is guaranteed to be closed.
valwith_open_text : string->(t->'a)->'a
Like Out_channel.with_open_bin , but the channel is opened in text mode (see Out_channel.open_text ).
valwith_open_gen : open_flaglist->int->string->(t->'a)->'a
Like Out_channel.with_open_bin , but can specify the opening mode and file permission, in case the file
must be created (see Out_channel.open_gen ).
valclose : t->unit
Close the given channel, flushing all buffered write operations. Output functions raise a Sys_error
exception when they are applied to a closed output channel, except Out_channel.close and
Out_channel.flush , which do nothing when applied to an already closed channel. Note that
Out_channel.close may raise Sys_error if the operating system signals an error when flushing or closing.
valclose_noerr : t->unit
Same as Out_channel.close , but ignore all errors.
Outputvaloutput_char : t->char->unit
Write the character on the given output channel.
valoutput_byte : t->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.
valoutput_string : t->string->unit
Write the string on the given output channel.
valoutput_bytes : t->bytes->unit
Write the byte sequence on the given output channel.
Advancedoutputvaloutput : t->bytes->int->int->unitoutputocbufposlen writes len characters from byte sequence buf , starting at offset pos , to the
given output channel oc .
RaisesInvalid_argument if pos and len do not designate a valid range of buf .
valoutput_substring : t->string->int->int->unit
Same as Out_channel.output but take a string as argument instead of a byte sequence.
valoutput_bigarray : t->('a,Bigarray.int8_unsigned_elt,Bigarray.c_layout)Bigarray.Array1.t->int->int->unit
Same as Out_channel.output but take the data from a bigarray.
Since 5.2
Flushingvalflush : t->unit
Flush the buffer associated with the given output channel, performing all pending writes on that channel.
Interactive programs must be careful about flushing standard output and standard error at the right time.
valflush_all : unit->unit
Flush all open output channels; ignore errors.
Seekingvalseek : t->int64->unitseekchanpos 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.
valpos : t->int64
Return the current writing position for the given channel. Does not work on channels opened with the
Open_append flag (returns unspecified results).
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 Out_channel.pos , then going back to this
position using Out_channel.seek will not work. For this programming idiom to work reliably and portably,
the file must be opened in binary mode.
Attributesvallength : 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.
valset_binary_mode : t->bool->unitset_binary_modeoctrue sets the channel oc to binary mode: no translations take place during output.
set_binary_modeocfalse sets the channel oc to text mode: depending on the operating system, some
translations may take place during output. For instance, under Windows, end-of-lines will be translated
from \n to \r\n .
This function has no effect under operating systems that do not distinguish between text mode and binary
mode.
valis_binary_mode : t->boolis_binary_modeoc returns whether the channel oc is in binary mode (see Out_channel.set_binary_mode ).
Since 5.2
valset_buffered : t->bool->unitset_bufferedoctrue sets the channel oc to buffered mode. In this mode, data output on oc will be
buffered until either the internal buffer is full or the function Out_channel.flush or
Out_channel.flush_all is called, at which point it will be sent to the output device.
set_bufferedocfalse sets the channel oc to unbuffered mode. In this mode, data output on oc will be
sent to the output device immediately.
All channels are open in buffered mode by default.
valis_buffered : t->boolis_bufferedoc returns whether the channel oc is buffered (see Out_channel.set_buffered ).
valisatty : t->boolisattyoc is true if oc refers to a terminal or console window, false otherwise.
Since 5.1
Examples
Writing the contents of a file:
letwrite_filefiles=Out_channel.with_open_binfile(funoc->Out_channel.output_stringocs))
OCamldoc 2025-06-12 Stdlib.Out_channel(3o)
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