这是一篇讲解只用OCaml标准库中提供的操作来实现基本文件操作的指南。
This is a guide to basic file manipulation in OCaml using only what the standard library provides.
请看官方模块文档:Pervasives, Printf.
标准库不提供可以直接读取文件成字符串或保存字符串到文件中的函数。这样的函数可以在第三方类如Extlib找到. 请见 Std.input_file与 Std.output_file.
The normal way of opening a file in OCaml returns a channel. There are two kinds of channels:
out_channel
in_channel
For writing into a file, you would do this:
out_channel
Commonly used functions: open_out
, open_out_bin
, flush
, close_out
, close_out_noerr
Standard out_channel
s: stdout
, stderr
For reading data from a file you would do this:
in_channel
End_of_file
exception is raised. Often, this is where you want to close the channel.Commonly used functions: open_in
, open_in_bin
, close_in
, close_in_noerr
Standard in_channel
: stdin
Whenever you write or read something to or from a channel, the current position changes to the next character after what you just wrote or read. Occasionally, you may want to skip to a particular position in the file, or restart reading from the beginning. This is possible for channels that point to regular files, use seek_in
or seek_out
.
out_channel
s if you want to actually write something. This is particularly important if you are writing to non-files such as the standard output (stdout
) or a socket.Unix
module provides access to non-buffered file descriptors among other things. It provides standard file descriptors that have the same name as the corresponding standard channels: stdin
, stdout
and stderr
. Therefore if you do open Unix
, you may get type errors. If you want to be sure that you are using the stdout
channel and not the stdout
file descriptor, you can prepend it with the module name where it comes from: Pervasives.stdout
. Note that most things that don't seem to belong to any module actually belong to the Pervasives
module, which is automatically opened.
open_out
and open_out_bin
truncate the given file if it already exists! Use open_out_gen
if you want an alternate behavior.open Printf let file = "example.dat" let message = "Hello!" let _ = (* 向文件写信息 *) let oc = open_out file in (* 新建或修改文件,返回通道 *) fprintf oc "%s\n" message; (* 写一些东西 *) close_out oc; (* 写入并关闭通道 *) (* 读取文件并显示第一行 *) let ic = open_in file in try let line = input_line ic in (* 从输入通道读入一行并丢弃'\n'字符 *) print_endline line; (* 输出结果到标准输出端 *) flush stdout; (* 现在写入默认设备 *) close_in ic (* 关闭输入通道 *) with e -> (* 一些不可预见的异常发生 *) close_in_noerr ic; (* 紧急关闭 *) raise e (* 以出错的形式退出: 文件已关闭,但通道没有写入东西 *) (* 正常退出: 所有的通道都已写入且关闭 *)
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