I use this code to write a string to a file.
var fs = File.Open(path, FileMode.OpenOrCreate, FileAccess.Write);
var sw = new StreamWriter(fs, Encoding.UTF8);
sw.Write(dataString);
fs.Flush();
sw.Flush();
sw.Close();
When I debug it, I see the dataString correct. However, after writing to a file, there are some strings have wrong orders. Should I add a thread Sleep after writing data to the file because right after writing data to the file, I read it back for other process.
OR probably there is better way to write a string to a file?
Thanks in advance.
OR probably there is better way to write a string to a file?
Yes, there's a simpler way. Use File.WriteAllText or File.AppendAllText.
File.WriteAllText("output.txt", text, Encoding.UTF8);
Apart from being more concise, another advantage is that the file will be correctly closed even if there is an exception. However, I doubt that it will change the order in which the data is written to the file.
Related
What is the best way to replace text in a text file?
I do not want to give the file a new name
I do not want the text to become one long string which is what happens when I use File.ReadAllText because this is stored as a string and I loose carriage returns etc...
Also, I guess I will run into issues using a StreamReader/StreamWriter because you cannot read and write to the same file?
Thanks
You can do it with a stream opened for both reading and writing:
FileStream fileStream = new FileStream(#"c:\myFile.txt", FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.None);
var streamWriter = new StreamWriter(fileStream);
var streamReader = new StreamReader(fileStream);
...
fileStream .Close();
But the most easy way is still to read all file, edit the text and write it back to the file:
var text = File.ReadAllText(#"c:\myFile.txt");
...
File.WriteAllText(#"c:\myFile.tx", text);
Depending on your file format, you could also read your files line by line (using File.ReadLines) and perform the text replacements for each line.
You can also refer to this answer for a variant based on streams, which is the preferred way if your file is large.
How to read a large (1 GB) txt file in .NET?
I have a few files in \AppData\Roaming that my app is writing to. I create the files when the application starts like this:
private void Form1_Load(object sender, EventArgs e)
{
DirectoryInfo _File = new DirectoryInfo(Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), #"MyApp\myfile.txt"));
}
Later, when I write to the file with a button click, I get an error saying that the file is already in use and cannot be accessed. How would I fix this?
The code to write to the file is correct because when I remove the code above and make the files myself, the application writes to them without any issues. Therefore, I dont think the problem is with the code I use to write to the files. But, here it is for reference:
var myfile = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), #"MyApp\myfile.txt"));
StreamWriter sw = new StreamWriter(myfile);
sw.WriteLine(textBox1.text);
sw.Close();
Thanks in advance for any help!
There are a few concepts at play here and I am not sure that we have enough information to definitively address the root problem, but I will give you a few pointers.
You need to be aware of the FileMode, FileAccess and FileShare enumerations.
The first, FileMode, specifies what you intend to do with regard to the file's existence. There are various options, documented in the link above. mI don't think that you have a problem here, but it bears mentioning.
The second, FileAccess, concerns your intended interaction with the file (read, write, or both). If you ask for access to read, then anyone else who opens the file or had it open already (including that web browser control) must have allowed sharing with other readers.
The final one, FileShare, defines who you are willing to share access to the file with. You can specify that others can read it, others can write to it, both, or neither.
The code that you are using is accessing the file using the very simplest defaults, which may be incompatible with the WebBrowser's access mode. Here's what I'd suggest instead:
var myfile = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), #"MyApp\myfile.txt"));
using (var fs = new FileStream(myfile, FileMode.OpenOrCreate, FileAccess.Write, FileShare.ReadWrite)) {
using (var sw = new StreamWriter(fs)) {
// You probably want to move to the end of the file before writing...
fs.Seek(0, SeekOrigin.End);
sw.WriteLine(textBox1.text);
sw.Close();
}
}
This very clearly expresses your intent, as well as the fact that you are willing to share with others who might read or write (we know the webbrowser will not write to the file, but for some reason maybe it is trying to open it with write intent anyway).
For file operations (as well as anytime your are accessing unmanaged resources) your best bet is to only grab a handle to the file long enough to perform the operation you want and then release it.
In your case, you are opening the resource, then trying to open it again later. Change this. Don't create the files until you are actually going to do something with it. Also, look into the USING clause. You want to release it as soon as you are done reading or writing from it.
Try to Access the FileInfo object to create/append/write files as follows, the file is already been taken by FileInfo class,
use as following,
FileInfo fi1 = new FileInfo(path);
//Create a file to write to.
using (StreamWriter sw = fi1.CreateText())
{
sw.WriteLine("Hello");
sw.WriteLine("And");
sw.WriteLine("Welcome");
}
//Open the file to read from.
using (StreamReader sr = fi1.OpenText())
{
string s = "";
while ((s = sr.ReadLine()) != null)
{
Console.WriteLine(s);
}
}
Try using using.
using (StreamWriter sw = new StreamWriter(myfile))
{
sw.Write(textBox1.text);
}
I wanna to have the ability to write an XML file with XmlTextWriter or LINQ to XML but by the way I don't want the file to be locked completely. I wanna the other processes to be able to read the Xml file. It should be locked only in write mode so that the others may not modify the file.
What is the best way to achieve this ?
You need to set this when you open the FileStream. Try this:
var fs = new FileStream(path, FileMode.OpenOrCreate, FileAccess.Write, FileShare.Read);
var xmlWriter = XmlWriter.Create(fs);
As Yahia mentions, there is no guarantee that the data written at any point will be meaningful to a reader.
I need to create a large text document. I currently use StringBuilder to make the document and then call File.WriteallText(filename,sb.ToString). Unfortunately, this is now starting to throw out of memory exceptions.
Is there a better way to stream a StringBuilder to file or is there some other technique I should be using?
Instead of using StringBuilder, try using TextWriter (which has a broadly similar API, but which can write to a number of underlying destinations, including files) - i.e.
using(TextWriter writer = File.CreateText(path))
{
// loop etc
writer.Write(...);
}
More generally, it is worth separating the code that knows about files from the code that knows about how to write the data, i.e.
using(var writer = File.CreateText(path))
{
Serialize(writer);
}
...
void Serialize(TextWriter writer)
{
...
}
this makes it easier to write to different targets. For example, you can now do in-memory too:
var sw = new StringWriter();
Serialize(sw);
string text = sw.ToString();
The point being: your Serialize code didn't need to change to accomodate a different target. This could also be writing directly to a network, or writing through a compression/encryption stream. Very versatile.
Just use a StreamWriter that writes to a FileStream:
using (StreamWriter writer = new StreamWriter("filename.txt")) {
...
}
This will of course mean that you can't change the text that is already written, like you can do in a StringBuilder, but I assume that you are not using that anyway.
Why not streaming directly into the stream?
You could use the TextWriter.
You can use StreamWriter and write to the file directly.
How does one clear the contents of a file?
You can use the File.WriteAllText method.
System.IO.File.WriteAllText(#"Path/foo.bar",string.Empty);
This is what I did to clear the contents of the file without creating a new file as I didn't want the file to display new time of creation even when the application just updated its contents.
FileStream fileStream = File.Open(<path>, FileMode.Open);
/*
* Set the length of filestream to 0 and flush it to the physical file.
*
* Flushing the stream is important because this ensures that
* the changes to the stream trickle down to the physical file.
*
*/
fileStream.SetLength(0);
fileStream.Close(); // This flushes the content, too.
Use FileMode.Truncate everytime you create the file. Also place the File.Create inside a try catch.
The easiest way is:
File.WriteAllText(path, string.Empty)
However, I recommend you use FileStream because the first solution can throw UnauthorizedAccessException
using(FileStream fs = File.Open(path,FileMode.OpenOrCreate, FileAccess.ReadWrite))
{
lock(fs)
{
fs.SetLength(0);
}
}
Try using something like
File.Create
Creates or overwrites a file in the
specified path.
The simplest way to do this is perhaps deleting the file via your application and creating a new one with the same name... in even simpler way just make your application overwrite it with a new file.