How do I write a text file from within a C# ASP.NET page?

Question

I'm coming to C# ASP.NET from Ruby and PHP, and I'm enjoying some elements of it but am finding certain things difficult to achieve. It's a bit different to get my head around, and I'd really appreciate it if someone could help me get this bit up and running.

I am trying to take some text sent in a POST request, HTML-escape it, and then write it to a text file.

So I look it up, read a little, and try:

<% 
    System.IO.StreamWriter file = new System.IO.StreamWriter(Server.MapPath(@"./messager.txt"));
    file.WriteLine(Request.Form["message"]);
    file.Close();
%>

Not doing the HTML-escaping yet, just trying to actually write to the text file.

This doesn't work, though; it throws no error that I can see, but just does nothing, the text file isn't written to at all. I've researched the methods and can't really figure out why. I would really love some help.

If it helps, here is working Ruby code for what I am trying to do:

File.open "messager.txt", "w" {|f| f.puts h params[:message]}

Did you try a backslash (\) in the path instead of forward slash (/)? — dotNET
– dotNET, Commented Dec 18, 2014 at 7:36
@FabrizioAccatino I'm not getting an error; the text file simply isn't being written to. — GreenTriangle
– GreenTriangle, Commented Dec 18, 2014 at 8:26
@dotNET I've just tried that, unfortunately with no change. It's worth pointing out that System.IO.File.ReadAllText(Server.MapPath(@"~\messager.txt")) does work so I don't think the path ist he problem. — GreenTriangle
– GreenTriangle, Commented Dec 18, 2014 at 8:27
I would recommend to do that in code behind since it is not ruby or php or asp. asp.net isn't meant to be used like this. — Ktt
– Ktt, Commented Dec 18, 2014 at 9:25

Community · Accepted Answer · 2020-06-20 09:12:55Z

2

You have to provide a virtual path relative to the web app when using Server.MapPath using the special character ~ which is a shortcut to the web app root directory. Now, the simplest way to do it is a follows...

System.IO.File.WriteAllText(Server.MapPath("~\messager.txt"), Request.Form["message"]);

this is assuming that the request actually contains the "message" form variable. Note that this approach will create a new file if it doesn't exist or will override it if it does exist.

However, in ASP.NET Web Forms we usually use server controls such as a TextBox, if when posting the page the message is set to a text box, then a better way to retrieve this message in OOP-style would be...

TextBox_ID.Text;

where TextBox_ID is the id of the TextBox

Edit

if Request.Form["message"] is coming in empty. Make sure that:

there's a text input element named message
there's no other element with the same name attribute
the input element is inside the form tag with runat=server attribute
you are posting back the page instead of issuing a GET request

edited Jun 20, 2020 at 9:12

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answered Dec 18, 2014 at 7:41

Leo

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1 Comment

GreenTriangle Over a year ago

Thanks for your reply, I appreciate it. I've tried using the code sample you provided, but it doesn't work; nothing is written to the text file. This makes me think something is wrong with the way I'm posting data. I am sending a simple HTML form, where a text input element named 'message' is submitted to the page this ASP.NET code is embedded on. Is Request.Form["message"] not the correct way to access information sent in this way?

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