How to read an entire file to a string using C#?

Question

What is the quickest way to read a text file into a string variable?

I understand it can be done in several ways, such as read individual bytes and then convert those to string. I was looking for a method with minimal coding.

Legging

Check this #2855835 – Syllogistic

Check this: codingfusion.com/Post/How-to-Read-a-Text-File-in-ASP-NET-MVC – Isopropyl

Answer 1

How about File.ReadAllText:

string contents = File.ReadAllText(@"C:\temp\test.txt");

Cardcarrying

Not the best function to use, though. As Devendra D. Chavan points out in his answer, StreamReader.ReadToEnd is more efficient. – Luger

@OwenBlacker It depends on whether "quickest" means "least time to execute" or "least time to understand." – Raft

File.ReadAllText is definitively the easiest one to use, but as "Devendra D. Chavan" points out, it is not the fastest. So if you are reading small files, then it would be a better choice to use File.ReadAllText.it really depends on how big the textfiles are that you are reading. – Estellestella

To read from the server check this, hope helps someone. – Jilleen

When developing and you need to load some data, this is good enough. It's easy to use for something temporary that will be removed eventually. – Raddie

@OwenBlacker -- are you sure? The benchmark shows that StreamReader.ReadToEnd is more efficient than ReadAllLines. Which is to be expected, as the latter also splits the text into lines. But we are talking about a different method, ReadAllText. Indeed the answer you mention shows that ReadAllText just calls StreamReader.ReadToEnd internally. – Ogre

Answer 2

A benchmark comparison of File.ReadAllLines vs StreamReader ReadLine from C# file handling

Results. StreamReader is much faster for large files with 10,000+ lines, but the difference for smaller files is negligible. As always, plan for varying sizes of files, and use File.ReadAllLines only when performance isn't critical.

StreamReader approach

As the File.ReadAllText approach has been suggested by others, you can also try the quicker (I have not tested quantitatively the performance impact, but it appears to be faster than File.ReadAllText (see comparison below)). The difference in performance will be visible only in case of larger files though.

string readContents;
using (StreamReader streamReader = new StreamReader(path, Encoding.UTF8))
{
     readContents = streamReader.ReadToEnd();
}

Comparison of File.Readxxx() vs StreamReader.Readxxx()

Viewing the indicative code through ILSpy I have found the following about File.ReadAllLines, File.ReadAllText.

• File.ReadAllText - Uses StreamReader.ReadToEnd internally
• File.ReadAllLines - Also uses StreamReader.ReadLine internally with the additionally overhead of creating the List<string> to return as the read lines and looping till the end of file.

So both the methods are an additional layer of convenience built on top of StreamReader. This is evident by the indicative body of the method.

File.ReadAllText() implementation as decompiled by ILSpy

public static string ReadAllText(string path)
{
    if (path == null)
    {
        throw new ArgumentNullException("path");
    }
    if (path.Length == 0)
    {
        throw new ArgumentException(Environment.GetResourceString("Argument_EmptyPath"));
    }
    return File.InternalReadAllText(path, Encoding.UTF8);
}   

private static string InternalReadAllText(string path, Encoding encoding)
{
    string result;
    using (StreamReader streamReader = new StreamReader(path, encoding))
    {
        result = streamReader.ReadToEnd();
    }
    return result;
}

Violet

Did you compare against File.ReadAllText, too ?? – Cardcarrying

ILSpy suggests that File.ReadAllText() is simply a wrapper over StreamReader.ReadToEnd(). I am guessing that the additional layer should perform slightly slower than StreamReader.ReadToEnd(). – Violet

Great answer. Perhaps a little bit much explanation for those just looking for the fix, but it deserves at least as many votes as the chosen answer. – Overshoe

@Devendra D. Chavan: Offtopic, but where can I find reference or documentation for ILSpy? – Tucana

You can also find the code here: referencesource.microsoft.com/#mscorlib/system/io/…. What I don't get, is why there is this significant difference in speed if ReadAllText is just a wrapper for streamReader.ReadToEnd();? – Cavafy

Answer 3

string contents = System.IO.File.ReadAllText(path)

Here's the MSDN documentation

Ademption

Answer 4

For the noobs out there who find this stuff fun and interesting, the fastest way to read an entire file into a string in most cases (according to these benchmarks) is by the following:

using (StreamReader sr = File.OpenText(fileName))
{
        string s = sr.ReadToEnd();
}
//you then have to process the string

However, the absolute fastest to read a text file overall appears to be the following:

using (StreamReader sr = File.OpenText(fileName))
{
        string s = String.Empty;
        while ((s = sr.ReadLine()) != null)
        {
               //do what you have to here
        }
}

Put up against several other techniques, it won out most of the time, including against the BufferedReader.

Japonica

Comment is late I know, but a little confused on your benchmarks here and on the linked page. It appears to be testing read speeds only and not loading into an entire string. The second code snippet is reading a line at a time and not doing any appending so the "do what you have to here" would need to have a string builder or string to hold the data. At which point the memory used to add more data would change the test results. So s will usually be the same size assuming a fixed width file so the memory will be set for the size of a line and data won't need to be copied to new memory. – Mayhap

I downvoted this comparison because they're looking at two different things. The first one gets the whole file into a string. The second one reads line-by-line, never having the whole file in a single string -- and not matching the "how to read an entire file to a string" question. – Anagrammatize

Answer 5

Take a look at the File.ReadAllText() method

Some important remarks:

This method opens a file, reads each line of the file, and then adds each line as an element of a string. It then closes the file. A line is defined as a sequence of characters followed by a carriage return ('\r'), a line feed ('\n'), or a carriage return immediately followed by a line feed. The resulting string does not contain the terminating carriage return and/or line feed.

This method attempts to automatically detect the encoding of a file based on the presence of byte order marks. Encoding formats UTF-8 and UTF-32 (both big-endian and little-endian) can be detected.

Use the ReadAllText(String, Encoding) method overload when reading files that might contain imported text, because unrecognized characters may not be read correctly.

The file handle is guaranteed to be closed by this method, even if exceptions are raised

Constitute

Answer 6

string text = File.ReadAllText("Path"); you have all text in one string variable. If you need each line individually you can use this:

string[] lines = File.ReadAllLines("Path");

Digitalize

Answer 7

System.IO.StreamReader myFile =
   new System.IO.StreamReader("c:\\test.txt");
string myString = myFile.ReadToEnd();

Dunghill

Answer 8

if you want to pick file from Bin folder of the application then you can try following and don't forget to do exception handling.

string content = File.ReadAllText(Path.Combine(System.IO.Directory.GetCurrentDirectory(), @"FilesFolder\Sample.txt"));

Tetter

Answer 9

@Cris sorry .This is quote MSDN Microsoft

Methodology

In this experiment, two classes will be compared. The StreamReader and the FileStream class will be directed to read two files of 10K and 200K in their entirety from the application directory.

StreamReader (VB.NET)

sr = New StreamReader(strFileName)
Do
  line = sr.ReadLine()
Loop Until line Is Nothing
sr.Close()

FileStream (VB.NET)

Dim fs As FileStream
Dim temp As UTF8Encoding = New UTF8Encoding(True)
Dim b(1024) As Byte
fs = File.OpenRead(strFileName)
Do While fs.Read(b, 0, b.Length) > 0
    temp.GetString(b, 0, b.Length)
Loop
fs.Close()

Result

FileStream is obviously faster in this test. It takes an additional 50% more time for StreamReader to read the small file. For the large file, it took an additional 27% of the time.

StreamReader is specifically looking for line breaks while FileStream does not. This will account for some of the extra time.

Recommendations

Depending on what the application needs to do with a section of data, there may be additional parsing that will require additional processing time. Consider a scenario where a file has columns of data and the rows are CR/LF delimited. The StreamReader would work down the line of text looking for the CR/LF, and then the application would do additional parsing looking for a specific location of data. (Did you think String. SubString comes without a price?)

On the other hand, the FileStream reads the data in chunks and a proactive developer could write a little more logic to use the stream to his benefit. If the needed data is in specific positions in the file, this is certainly the way to go as it keeps the memory usage down.

FileStream is the better mechanism for speed but will take more logic.

Ampliate

But what about StreamReader.ReadToEnd ? – Luger

Answer 10

well the quickest way meaning with the least possible C# code is probably this one:

string readText = System.IO.File.ReadAllText(path);

Latreshia

Answer 11

you can use :

 public static void ReadFileToEnd()
{
    try
    {
    //provide to reader your complete text file
        using (StreamReader sr = new StreamReader("TestFile.txt"))
        {
            String line = sr.ReadToEnd();
            Console.WriteLine(line);
        }
    }
    catch (Exception e)
    {
        Console.WriteLine("The file could not be read:");
        Console.WriteLine(e.Message);
    }
}

Ronnie

Answer 12

string content = System.IO.File.ReadAllText( @"C:\file.txt" );

Thyself

Answer 13

You can use like this

public static string ReadFileAndFetchStringInSingleLine(string file)
    {
        StringBuilder sb;
        try
        {
            sb = new StringBuilder();
            using (FileStream fs = File.Open(file, FileMode.Open))
            {
                using (BufferedStream bs = new BufferedStream(fs))
                {
                    using (StreamReader sr = new StreamReader(bs))
                    {
                        string str;
                        while ((str = sr.ReadLine()) != null)
                        {
                            sb.Append(str);
                        }
                    }
                }
            }
            return sb.ToString();
        }
        catch (Exception ex)
        {
            return "";
        }
    }

Hope this will help you.

Gerdy

Answer 14

you can read a text from a text file in to string as follows also

string str = "";
StreamReader sr = new StreamReader(Application.StartupPath + "\\Sample.txt");
while(sr.Peek() != -1)
{
  str = str + sr.ReadLine();
}

Handkerchief

Answer 15

I made a comparison between a ReadAllText and StreamBuffer for a 2Mb csv and it seemed that the difference was quite small but ReadAllText seemed to take the upper hand from the times taken to complete functions.

Angelangela

Answer 16

I'd highly recommend using the File.ReadLines(path) compare to StreamReader or any other File reading methods. Please find below the detailed performance benchmark for both small-size file and large-size file. I hope this would help.

File operations read result:

For small file (just 8 lines)

For larger file (128465 lines)

Readlines Example:

public void ReadFileUsingReadLines()
{
    var contents = File.ReadLines(path);
}

Note : Benchmark is done in .NET 6.

Crescint

Answer 17

This comment is for those who are trying to read the complete text file in winform using c++ with the help of C# ReadAllText function

using namespace System::IO;

String filename = gcnew String(charfilename);
if(System::IO::File::Exists(filename))
{
     String ^ data = gcnew String(System::IO::File::RealAllText(filename)->Replace("\0", Environment::Newline));
     textBox1->Text = data;
}

Pandect