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.NET Forum / .NET Framework / New Users / December 2005how do i create a new file -- in memory?
hello, i have what i would guess to be a relatively "newbie" question: how do i create & write to a new text file? i have found plenty of articles (MSDN & other) on how to do this in conjuction w/ the *file system*, but i do not wish to touch the client's hard drive. rather, id like to build up a .txt file in memory, then Response.WriteFile() it back to the user (ASP.NET plaform). there are so many streams it's somewhat confusing. a high-level point or link to an article would be most helpful. thanks! matt > id like to build up a .txt file in memory > > there are so many streams it's somewhat confusing. a high-level point > or link to an article would be most helpful. MemoryStream? are you asking a question? ok, so i can use this syntax to write: MemoryStream ms = new MemoryStream(); StreamWriter sw = new StreamWriter(ms); foreach (DataRow row in _dtResults.Rows) { sw.WriteLine("foo"); } ..got that part. but then what do to change that memorystream into a file? the Response.WriteFile() method takes in either a file, or a "IntPtr fileHandler", which i am not familar with. is there a way to convert a stream into a new file? the File constructor doesnt seem to take a stream as a parameter. thanks! ah.. ok, i dont think the memorystream is really needed. atleast in my case... since i am return this to the web user, i can do so: //build file's contents StrinbBuilder sb = new StringBuilder(50); foreach (DataRow row in _dtResults.Rows) { sb.Append("foo"); sb.Append("\n"); } //send file to user Response.Clear(); Response.ContentType = "application/octet-stream"; Response.AppendHeader("content-disposition", "attachment; filename=foo.text"); Response.Flush(); Response.Write(fileContents); Response.End(); (tho i am still curious about how one takes a memorystream and turns it into a file object) matt It's a bit difficult, the beta WinFX SDK completely messed my C# express & WebExpress documentation... :-( basically you should use HttpResponse.Write (String) and build the string with an in memory stream. How to do that? here is some pseudo code (caution: name of the actors could have been modified) // 1st create the memory stream to write to MemoryStream ms = new MemoryStream(); StreamWriter sw = new StreamWriter(ms, Encoding.UTF8); // 2nd fill it up sw.WriteLine("blah blah blah"); sw.WriteLine("foo bar foo bar foo bar foo bar"); // 3rd get its content! ms.Position = 0; StreamReader sr = new StreamReader(ms, Encoding.UTF8); string content = sr.ReadToEnd(); // 4th write it to the user HttpResponse.Write(content); > ah.. ok, i dont think the memorystream is really needed. atleast in my > case... since i am return this to the web user, i can do so: [quoted text clipped - 22 lines] > > matt yeah, psuedo code is great, thanks. now looking at that.. doesnt it seem much heavier than the above (stringbuilder, response.write)...? thanks, matt ho, oops.... 1st. I missed the part with the StringBuilder. You keep changing variable names, that confuses me! just to make it clear: yep, you could write StringBuilder sb; Response.Write(sb.ToString()) it's even better in this case in your case!. 2dn: I was addressing your question about MemoryStream. Showing you how to work with them. Of course my pseudo-code is much heavier than your StringBuilder version but it's also much more extensible / flexible. On top of that, as you seems to be not very knowledgeable in the Stream area, it shows some usage of Stream chaining, which is a powerfull lego concept. > yeah, psuedo code is great, thanks. > [quoted text clipped - 3 lines] > thanks, > matt doh! i put my example together from two different tests, thus the mis-named variables. sorry. ah.. yes. thanks for the pointers on the stream. thats good to know about the memorywriter & streamreader. but, what about working w/ a File obj -- does a File *have* to be linked to the file system (ie, harddrive)? i wonder if one can build-up a text file via the MemoryStream as in your example, and then convert it somehow into a File, say if that's what some other function requires for further manipulation. (this is not my present scenario, but is interesting nonetheless). thanks again for the tips. matt > doh! i put my example together from two different tests, thus the > mis-named variables. sorry. Oki doki! > but, what about working w/ a File obj -- does a File *have* to be > linked to the file system (ie, harddrive)? i wonder if one can build-up > a text file via the MemoryStream as in your example, and then convert > it somehow into a File, say if that's what some other function requires > for further manipulation. (this is not my present scenario, but is > interesting nonetheless). You get me lost here. It's very confusing the way you say "only File".... Here is a list of what you could call a file and their possible source. I think I get most of them, but I might have missed what you were thinking about, who knows? .NET: System.IO.Stream: could be anything, including a MemoryStream as shown .NET: System.IO.FileStream: typically only a file system file .NET / C: string: filename: has to be a file system file in most case. (well could be a pipe or a printer port, etc... but it's seldom the case) C: HANDLE: many thing (socket, pipe, memoy mapped file, file system file, com port, printer port, etc...) but typically, when created by the user, a file system file. However, with some effort, could be a memory mapped file with no file system representation. .NET: IntPtr (point to a Handle): as above. So, look at the various signature of your methods/functions and you get your answer. if you don't know what you're speaking about, you can't tell! > It's very confusing the way you say "only File".... ...now im confused: there is no reference to "only File" except in your message.. :) in all the examples ive seen of working w/ the System.IO.File class, it's linked to a file residing on the file system. what im saying is, i wonder if it's possible to instantiate a File object that does *not* use the file system, but rather, uses something youve built-up in a memorystream. for example, say Function A works takes in a System.IO.File and does some processing with it. im wondering if Function B can *make* a System.IO.File (without a file on the file system. just using a memory stream), and then pass it to Function A. make sense? matt >> It's very confusing the way you say "only File".... > > ...now im confused: there is no reference to "only File" except in your > message.. :) > > in all the examples ive seen of working w/ the System.IO.File class, I told you it was confusing! You can't instantiate "System.IO.File"! So what do you want to do with it? > I told you it was confusing! yes! hmmm...totally not following you -- i instantiate (System.IO.)File objects all the time. based off of text files from the file system... i was just wondering if an in-memory stream can be turned into a System.IO.File object, but im begining to think no it cannot -- i think the System.IO.File is tied to the filesystem, and cannot be used w/ an im-memory-only file you created w/ a stream. thanks! matt I don't believe you! Post me a code sample! For exemple here is a compilable sample -- BUG.cs -- using System; class Foo { static void Main() { System.IO.File f = new System.IO.File(); Console.WriteLine(f); } } -- If I try csc /nologo BUG.cs => BUG.cs(6,9): error CS0723: Cannot declare variable of static type 'System.IO.File' BUG.cs(6,28): error CS0712: Cannot create an instance of the static class 'System.IO.File' -- Where you could see that CSC (the C# compiler) agree me (can't instantiate File). Are you using Java? if it does...... here is CSC version: C:\temp>csc Microsoft (R) Visual C# 2005 Compiler version 8.00.50215.44 for Microsoft (R) Windows (R) 2005 Framework version 2.0.50215 Copyright (C) Microsoft Corporation 2001-2005. All rights reserved. >> I told you it was confusing! > [quoted text clipped - 10 lines] > thanks! > matt BTW, here is what the documentation says: -- [ComVisibleAttribute(true)] public sealed abstract class File--So I'm curious as to how you instantiate an abstract class.... >> I told you it was confusing! > [quoted text clipped - 10 lines] > thanks! > matt my mistake. i was confusing FileInfo & File; Directory.GetFiles actually enumerates FileInfo, not File (i usually name the enum "file" so i forgot it wasnt the actual file). matt Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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