Develop Reference

C# How do I compare a string to a specific line in a file?

Let's say I have a string "Toast" and I want to check to see if line "n" of a text file contains that string. How do I go about this? I know "n"

Simple solution:
using(var reader = new StreamReader("MyFile.txt"))
{
string line;
int lineNumber = 0;
while((line = reader.ReadLine()) != null)
{
lineNumber++;
if (line.Contains("Toast"))
{
Console.WriteLine($"Found 'Toast' on line {lineNumber}");
}
}
}

Read text file and split it over

So, I know my headline is a bit confusing, I will explain.
My code looks like this:
string filename = "C:\\C#\\maplist.txt"; // please put the text file path.
string filename2 = "C:\\C#\\zemaplist.txt";
string map;
StreamReader sr = new StreamReader(filename);
StreamWriter sw = new StreamWriter(filename2);
List<string> maps = new List<string> { };
while ((map = sr.ReadLine()) != null)
{
maps.Add(map);
}
sr.Close();
for (int i = 0; i < maps.Count; i++)
{
Console.WriteLine(maps[i]);
sw.WriteLine(maps[i]);
}
sw.Close();
and what i need to do is when the code read a new line, in my line there is
"Hey,Hey"
I want to split the , from each other so I can take both of them as other parameters, so that the first Hey will be added to maps and the other hey will be maps2,
How can I do that?

You can use Split() function to Split the given String based on delimiter.
Try This:
while ((map = sr.ReadLine()) != null)
{
maps.Add(map.Split(',')[0].Trim());
maps2.Add(map.Split(',')[1].Trim());
}
Simple Code:
using System.IO;
string filename = "C:\\C#\\maplist.txt"; // please put the text file path.
string filename2 = "C:\\C#\\zemaplist.txt";
string map;
StreamWriter sw = new StreamWriter(filename2);
List<string> maps = new List<string> { };
List<string> maps2 = new List<string> { };
String [] allLines = File.ReadAllLines(filename);
foreach(String line in allLines)
{
maps.Add(line.Split(',')[0].Trim());
maps2.Add(line.Split(',')[1].Trim());
}
for (int i = 0; i < maps.Count; i++)
{
Console.WriteLine(maps[i]);
sw.WriteLine(maps[i]);
}
sw.Close();
Solution 2:
String mapItem1="";
String mapItem2="";
if(maps.Count == maps2.Count)
{
for(int i=0;i<maps.Count;i++)
{
mapItem1=maps[i];
mapItem2=maps2[i];
}
}

while ((map = sr.ReadLine()) != null)
{
string[] split = map.Split(',');
//First Hey would be split[0], second Hey would be split[1]
maps.Add(split[0].Trim());
maps2.Add(split[1].Trim());
}
The Split method should help you out with that.
If you want to trim leading whitespace characters, you can use the .Trim() method on a string.

Use Split().
string heys = "Hey,Hey";
string[] splitArray = heys.Split(',');
Then you have:
splitArray[0] = "Hey";
splitArray[1] = "Hey";

Why even bother reading line by line? Read the entire file, replace the new line chars for a "," (to prevent last and first elements from different lines to be treated as one), and loop through a clean string.
string fileContent = Regex.Replace(File.ReadAllText("test.txt"), #"\r", ",");
List<string> mapList = new List<string>();
foreach (string map in Regex.Split(fileContent.Replace(#"\s+", ""), ","))
{
mapList.Add(map.Trim());
}

Extract data from text file

I need to extract some data from a text file and insert to columns in excel sheet. I know how to do this if the rows and the length of the string is known.
try
{
using (System.IO.StreamReader sr = new System.IO.StreamReader("test.txt")
{
string line;
while ((line = sr.ReadLine()) != null)
{
listSNR.Items.Add(line.Substring (78,4));
}
}
}
But the particular text file is complex and the starting index or the length cannot be provided. But the starting word (PCPU01) of the row is known.
Eg: PCPU01,T2716,0.00,0.01,0.00,0.00
output:
T2716 0 0.01 0 0
In that case can somebody please let me know how to extract the texts?

using(System.IO.StreamReader sr = new System.IO.StreamReader("test.txt"))
{
string line;
while((line = sr.ReadLine()) != null)
{
string[] split = line.Split(',');
//...
}
}
split[0] will return "PCPU01", split[1] "T2716" and so on.

You can split one string into an array of strings, separated by a given character. This way, you could split the source string by a comma and use the resulting strings to build your output. Example:
string source = "PCPU01,T2716,0.00,0.01,0.00,0.00";
string[] parts = source.Split(',');
StringBuilder result = new StringBuilder();
result.Append(parts[1]); // The second element in the array, i.e. T2716
result.Append(" ");
result.Append(parts[2]); // 0.00
... // And so on...
return result.ToString() // return a string, not a StringBuilder

I hope this helps a little bit. You might have to tweak it to your needs. But this is a higher level code that gives you general idea of extracting data off a notepad.
DialogResult result = openFileDialog.ShowDialog();
Collection<Info> _infoCollection = new Collection<Info>();
Collection<string> listOfSubDomains = new Collection<string>();
string[] row;
string line;
// READ THE FILE AND STORE IT IN INFO OBJECT AND STORE TAHT INFO OBJECT IN COLLECTION
try
{
using (StreamReader reader = new StreamReader(openFileDialog.FileName))
{
while((line = reader.ReadLine()) != null)
{
Info _info = new Info();
row = line.Split(' ');
_info.FirstName = row[0];
_info.LastName = row[1];
_info.Email = row[2];
_info.Id = Convert.ToInt32(row[3]);
_infoCollection.Add(_info);
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}

thanks for the answers. What i wanted is to identify the particular line in the text file and split the line into columns. So i was able to do this by calling a GetLine method:
string line15=GetLine(#"test.txt",15);
public string GetLine(string fileName, int line)
{
using (System.IO.StreamReader ssr = new System.IO.StreamReader("test.txt"))
//using (var ssr = new StreamReader("test.txt"))
{
for (int i = 1; i < line; i++)
ssr.ReadLine();
return ssr.ReadLine();
}
}
Then i splitted this line by using the delimiter (,)

This was my approach in C#. It takes a string input (which you can get out of a text file) and an int with which line you want to get. It then separates the string at a given seperator char to a list which in turn is then read out. If the given line number is lower than the count of the created list, the entry is given back.
public string GetLine(string multiline,int line)
{
List<string> lines = new List<string>();
lines = multiline.Split('\n').ToList<string>();
return lines.Count >= line ? lines[line] : "";
}

Reading and changing a file

I'm reading a file using C# and class TextReader
TextReader reader = new StreamReader(stream);
string line;
while ((line = reader.ReadLine()) != null)
{
if (someCondition)
{
// I want to change "line" and save it into the file I'm reading from
}
}
In a code there is a question: how do I save a changed line to a file I'm reading from and continue reading?

Fast and dirty solution would be:
TextReader reader = new StreamReader(stream);
string line;
StringBuilder sb = new StringBuilder();
while ((line = reader.ReadLine()) != null)
{
if (someCondition)
{
//Change variable line as you wish.
}
sb.Append(line);
}
using (StreamWriter sw = new StreamWriter("filePath"))
{
sw.Write(sb.ToString());
}
or
TextReader reader = new StreamReader(stream);
string line;
String newLines[];
int index = 0;
while ((line = reader.ReadLine()) != null)
{
if (someCondition)
{
//Change variable line as you wish.
}
newLines[index] = line;
index++;
}
using (StreamWriter sw = new StreamWriter("filePath"))
{
foreach (string l in newLines)
{
sw.WriteLine(l);
}
}
If memory is too important you can try this too:
TextReader reader = new StreamReader(stream);
string line;
while ((line = reader.ReadLine()) != null)
{
if (someCondition)
{
//Change variable line as you wish.
}
using (StreamWriter sw = new StreamWriter("filePath"))
{
sw.WriteLine(line);
}
}

The easiest thing is to write a new file, then when finished, replace the old file with the new file. This way you only do writes in one file.
If you try to read/write in the same file, you will run into problems when the content you want to insert is not the exact same size as the content it is replacing.
There is nothing magic about text files. They are just a stream of bytes representing characters in a text encoding. There are no line concept in the file, just separators in the form of newline characters.

If the file is not too large, you should simply rewrite the whole file:
var lines = File.ReadAllLines(path)
.Where(l => someCondition);
File.WriteAllLines(path, lines);

A very simple solution
void Main()
{
var lines = File.ReadAllLines("D:\\temp\\file.txt");
for(int x = 0; x < lines.Length; x++)
{
// Of course this is an example of the condtion
// you should implement your checks
if(lines[x].Contains("CONDITION"))
{
lines[x] = lines[x].Replace("CONDITION", "CONDITION2");
}
}
File.WriteAllLines("D:\\temp\\file.txt", lines);
}
The drawback is the memory usage caused by the in memory lines, but, if we stay around 50MB, it should be handled effortlessly by modern PC.

Writing a specific line from one text file to other text file using c#

I Am using sharp develop. I am making a Win App using C# . I want my program check a text file named test in drive c: and find the line which contains "=" and then write this line to other newly created text file in drive c: .

Try this one-liner:
File.WriteAllLines(destinationFileName,
File.ReadAllLines(sourceFileName)
.Where(x => x.Contains("=")));

Here's another simple way using File.ReadLines, Linq's Where and File.AppendAllLines
var path1 = #"C:\test.txt";
var path2 = #"C:\test_out.txt";
var equalLines = File.ReadLines(path1)
.Where(l => l.Contains("="));
File.AppendAllLines(path2, equalLines.Take(1));

using(StreamWriter sw = new StreamWriter(#"C:\destinationFile.txt"))
{
StreamReader sr = new StreamReader(#"C:\sourceFile.txt");
string line = String.Empty;
while ((line = sr.ReadLine()) != null)
{
if (line.Contains("=")) { sw.WriteLine(line)); }
}
sr.Close();
}

Have you tried something?
Here are two ways to read a file:
Use static methods available in File class. ReadAllLines to be specific. This is good enough if you are dealing with small files. Next, once you have the array, just find the item with "=" using LINQ or by any other iteration method. Once you got the line, again use File class to create and write data to the file.
If you are dealing with large files, use Stream. Rest remains fairly same.

if (File.Exists(txtBaseAddress.Text))
{
StreamReader sr = new StreamReader(txtBaseAddress.Text);
string line;
string fileText = "";
while ((line = sr.ReadLine()) != null)
{
if (line.Contains("="))
{
fileText += line;
}
}
sr.Close();
if (fileText != "")
{
try
{
StreamWriter sw = new StreamWriter(txtDestAddress.Text);
sw.Write(fileText);
sw.Close();
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
}

a bit edited Furqan's answer
using (StreamReader sr = new StreamReader(#"C:\Users\Username\Documents\a.txt"))
using (StreamWriter sw = new StreamWriter(#"C:\Users\Username\Documents\b.txt"))
{
int counter = 0;
string line = String.Empty;
while ((line = sr.ReadLine()) != null)
{
if (line.Contains("="))
{
sw.WriteLine(line);
if (++counter == 4)
{
sw.WriteLine();
counter = 0;
}
}
}
}