Reading from a Text File in C#

Reading and parsing from a text file

Based on What's the fastest way to read a text file line-by-line? using a StreamReader to read line by line to minimize memory usage.

private void LoadSaveData()
{
    string fileName = @"c:\test.txt";
    const int BufferSize = 128;
    using (var fileStream = File.OpenRead(fileName))
    using (var streamReader = new StreamReader(fileStream, Encoding.UTF8, true, BufferSize))
    {
        string line;
        while ((line = streamReader.ReadLine()) != null)
        {
            // Process line
            string[] numberStrings = line.Split( );
            if(numberStrings.Length == 3
                && float.TryParse(numberStrings[0], out float f1)
                && float.TryParse(numberStrings[1], out float f2)
                && float.TryParse(numberStrings[2].TrimEnd(';'), out float f3))
            {
                // do something with your floats
            }
        }
    }
}

Reading a text file with c#

Hi Gailen use the following method:

File.ReadAllLines(@"location");

If location is correct then this will work
Assign to variable, for example

C# reading a string from text file, splitting and putting into tabstring

Your problem is here:

while (srListOfObjects.ReadLine() != null)
{
    string myString= (srListOfObjects.ReadLine();

You are entering the loop on the condition that srListOfObjects.ReadLine() returns something other than null but then you are immediately reading a new line form srListOfObjects and storing the returned reference in myString. This has obviously two problems:

The second call to ReadLine can return null and you are not checking if it is. The error you are getting is due to this reason.
You are losing information. You are ignoring the line you are reading when checking the while condition. Until your program crashes or runs to the end (depends on wether the input file has even or odd number of lines), you will process only half of the data.

Update:
You should only read one line per iteration. One way to do it is declaring and initializing myString before entering the loop and updating it on every iteration:

var myString = srListOfObjects.ReadLine();

while (myString != null)
{
    //do your stuff
    myString = srListOfObjects.ReadLine();
}

Read numbers from a text file in C#

Brannon's answer explains how to read binary data. If you want to read text data, you should be reading strings and then parsing them - for which there are built-in methods, of course.

For example, to read a file with data:

10
10.5
hello

You might use:

using (TextReader reader = File.OpenText("test.txt"))
{
    int x = int.Parse(reader.ReadLine());
    double y = double.Parse(reader.ReadLine());
    string z = reader.ReadLine();
}

Note that this has no error handling. In particular, it will throw an exception if the file doesn't exist, the first two lines have inappropriate data, or there are less than two lines. It will leave a value of null in z if the file only has two lines.

For a more robust solution which can fail more gracefully, you would want to check whether reader.ReadLine() returned null (indicating the end of the file) and use int.TryParse and double.TryParse instead of the Parse methods.

That's assuming there's a line separator between values. If you actually want to read a string like this:

10 10.5 hello

then the code would be very similar:

using (TextReader reader = File.OpenText("test.txt"))
{
    string text = reader.ReadLine();
    string[] bits = text.Split(' ');
    int x = int.Parse(bits[0]);
    double y = double.Parse(bits[1]);
    string z = bits[2];
}

Again, you'd want to perform appropriate error detection and handling. Note that if the file really just consisted of a single line, you may want to use File.ReadAllText instead, to make it slightly simpler. There's also File.ReadAllLines which reads the whole file into a string array of lines.

EDIT: If you need to split by any whitespace, then you'd probably be best off reading the whole file with File.ReadAllText and then using a regular expression to split it. At that point I do wonder how you represent a string containing a space.

In my experience you generally know more about the format than this - whether there will be a line separator, or multiple values in the same line separated by spaces, etc.

I'd also add that mixed binary/text formats are generally unpleasant to deal with. Simple and efficient text handling tends to read into a buffer, which becomes problematic if there's binary data as well. If you need a text section in a binary file, it's generally best to include a length prefix so that just that piece of data can be decoded.

c# read a text file. How to avoid reading it again

Like I said in my comment, just read the entire file once and save it into a List<string> using File.ReadAllLines() (Cast the output to a list). Once you have that, then you can just use the List<string> directly without having to go back to read the file each time. See below.

public class Program
{
    private static List<string> lines;
    public static void Main()
    {
        // At this point lines will have the entire file. Each line in a different index in the list
        lines = File.ReadAllLines("..path to file").ToList();

        useList(); // Use it however
    }

    // Just use the List which has the same data as the file
    public static string readFromList(int num)
    {
        return lines[num];
    } 

    public static void useList()
    {
        string line1 = readFromList(1); // Could even be string line1 = lines[SomeNum];
        string line2 = readFromList(2);
    }
}

Can not read from the text file specified in c#.net

The problem here is that your docPath variable doesn't hold the path to a single file, but instead the path of a folder. (C:\{User}\Documents)

So the File.Exists check will always fail, because you're targeting the folder.
Try combining your docPath with the actual file name and it should work.