How to implement “appendFile” function?

Question

I can use the following function to overwrite a text file:

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


        

Answer 1

This is what I do:

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

Answer 2

You could pass additional mode flag Open_append to open_out_gen function:

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