如何实现"appendFile“函数？

Question

我可以使用以下函数覆盖文本文件：

let writeFile ~filename:fn s =
let oc = open_out fn in
    output_string oc s;
    close_out oc ;;

但是，我不知道如何在文本文件中添加一行？

Answer 1

您可以将额外的模式标志Open_append传递给open_out_gen函数：

let _ =
    let oc = open_out_gen [Open_creat; Open_text; Open_append] 0o640 "a.txt" in
    output_string oc "append\n";
    close_out oc

Answer 2

这就是我要做的：

let append_string path s =
    let chan = open_out_gen [Open_wronly; Open_creat] 0o666 path
    in let len = out_channel_length chan
    in
        begin
        seek_out chan len;
        output_string chan s;
        close_out chan;
        end