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[C#] C# reading a text file - Printable Version

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+---- Thread: [C#] C# reading a text file (/showthread.php?tid=6006547)

C# reading a text file - DeadShot32 - Sep 9, 2019

I am looking how to read from a file search for the word then from that word put it in a textbox to a end word
like from date end paragraph

ty

RE: C# reading a text file - Bunnyslippers69 - Sep 10, 2019

You could do something similar to this:

Code
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;

namespace hfHelp1
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] lines = File.ReadAllLines("E:/Desktop/passwords.txt");
            foreach (var line in lines)
            {
                if (line.Contains("b"))
                {
                    Console.WriteLine(line);
                }
            }
        }
    }
}


RE: C# reading a text file - vaiperboy - Sep 10, 2019

(Sep 10, 2019 12:06 AM)Bunnyslippers69 Wrote:  You could do something similar to this:

Code
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;

namespace hfHelp1
{
   class Program
   {
       static void Main(string[] args)
       {
           string[] lines = File.ReadAllLines("E:/Desktop/passwords.txt");
           foreach (var line in lines)
           {
               if (line.Contains("b"))
               {
                   Console.WriteLine(line);
               }
           }
       }
   }
}
well thats not really a good way since it loads all of the lines into the memory, which sometimes can be useless (imagine if the word was found in the first line?) ,slow and being able to crash

also if I understood correctly you want to find where line a contains a certain word and return that line? if so,

@OP, you could load one line at a memory and checking that. This can be done by
Code
foreach (var line in File.ReadLines("path")) {
                if (line.Contains("word"))
                    break;
            }

or if you feeling linqy
Code
var lines = File.ReadLines("path")
                .Where(line => line.Contains("word"));

but thats just real basic. All depends on how big your file is, if you need faster stuff to handle bigger stuff look at https://github.com/pdonald/aho-corasick
FYI, the linq version searches for all occurrences

RE: C# reading a text file - MavenGradle - Sep 10, 2019

(Sep 10, 2019 12:06 AM)Bunnyslippers69 Wrote:  You could do something similar to this:

Code
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;

namespace hfHelp1
{
   class Program
   {
       static void Main(string[] args)
       {
           string[] lines = File.ReadAllLines("E:/Desktop/passwords.txt");
           foreach (var line in lines)
           {
               if (line.Contains("b"))
               {
                   Console.WriteLine(line);
               }
           }
       }
   }
}

No error handling and like vaiperboy pointed out this is very inefficient when dealing with very large files. Same goes for the LINQ method vaiperboy posted. It's just a prettier way to write all that code.

(Sep 10, 2019 09:42 AM)vaiperboy Wrote:  
Code
foreach (var line in File.ReadLines("path")) {
               if (line.Contains("word"))
                   break;
           }

If it's important that these files remain accessible while you're doing your thing, you might not want to use the File.ReadLines method because it will place a full on write block handle on the file. You might be more inclined to use a StreamReader like so:
Code
var fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
using (var sr = new StreamReader(fs))
{
   // etc...
}


RE: C# reading a text file - riu41776 - Sep 11, 2019

I suggest you to skip the comments above me as they're suggesting you primitive ways to search for a substring.

If you want to go professional, use regular expressions.

RE: C# reading a text file - DeadShot32 - Sep 14, 2019

Thank you much :) for your help

RE: C# reading a text file - riu41776 - Sep 15, 2019

I'm LMFAO'ing so hard from the usage of ".contains", you serious?

@OP use Regular expressions.

RE: C# reading a text file - n0s1eep - Sep 20, 2019

string.Contains is perfectly fine for this use case. Use of regexp is overkill, a professional programmer knows when to use the right tool for the right job.

RE: C# reading a text file - 0xDEAD10CC - Sep 21, 2019

(Sep 20, 2019 02:43 PM)n0s1eep Wrote:  string.Contains is perfectly fine for this use case. Use of regexp is overkill, a professional programmer knows when to use the right tool for the right job.

The above user has no clue what he's talking about so just ignore his idea to use regex. The guy can't even build a regex pattern to match duplicate words.

Use IndexOf and specify the appropriate string comparison enum value.

RE: C# reading a text file - max_int - Oct 3, 2019

Code
using System;
using System.IO;

namespace MyNullSpace
{
   class MyTextFinder
   {
       public static void IsStringInText(string fileName, string someText)
       {
               bool found = false;
               //the StreamReader class does not lock the file
               //-- so other processes can still access file-
               using (StreamReader sr = new StreamReader(fileName))
              {
                   while (!sr.EndOfStream)
                   {
                       string line = sr.ReadLine();
                        //for more complex match
                        //change the lines below to use regex
                        var comparer = StringComparer.InvariantCultureIgnoreCase;
                       if(line.Contains(someText, comparer))
                        {
                              found=true;
                              break;
                         }
                 }
              }
                return found;
            }
       }
}
This may help

RE: C# reading a text file - vaiperboy - Oct 4, 2019

(Oct 3, 2019 03:02 PM)max_int Wrote:  
Code
using System;
using System.IO;

namespace MyNullSpace
{
   class MyTextFinder
   {
       public static void IsStringInText(string fileName, string someText)
       {
              bool found = false;
              //the StreamReader class does not lock the file
              //-- so other processes can still access file-
              using (StreamReader sr = new StreamReader(fileName))
              {
                   while (!sr.EndOfStream)
                   {
                       string line = sr.ReadLine();
                       //for more complex match
                       //change the lines below to use regex
                       var comparer = StringComparer.InvariantCultureIgnoreCase;
                       if(line.Contains(someText, comparer))
                       {
                             found=true;
                             break;
                        }
                 }
              }
               return found;
           }
      }
}
This may help

I stopped reading when i saw found=true

RE: C# reading a text file - max_int - Oct 4, 2019

(Oct 4, 2019 06:53 AM)vaiperboy Wrote:  I stopped reading when i saw found=true
Can you explain please ?
I didn't pretend it was the most efficient way to do it.

RE: C# reading a text file - vaiperboy - Oct 4, 2019

(Oct 4, 2019 07:02 AM)max_int Wrote:  Can you explain please ?
I didn't pretend it was the most efficient way to do it.
I mean for one, its a void. How you returning a boolean to it?
secondly, for this piece of code
Code
if (line.Contains(someText, comparer)) {
                        found = true;
                        break;
                    }
                }
            }
            return found;
it doesnt make sense. Let's assume that this function is simply a function that returns true if it finds the 1st occurrence piece of word we're looking for, you just gotta return the true inside the while there.

Code
[code]
if (line.Contains(someText, comparer)) {
                        return true;
                    }
                }
            }
return false;
no need for any unnecessary code

RE: C# reading a text file - max_int - Oct 4, 2019

(Oct 4, 2019 07:16 AM)vaiperboy Wrote:  I mean for one, its a void. How you returning a boolean to it?
secondly, for this piece of code
Code
if (line.Contains(someText, comparer)) {
                       return true;
                   }
               }
           }
return false;
no need for any unnecessary code
I agree with the idea of returning immediately  when the string is found.
Anyway, in some cases, it may not be the best option
1. you need to do some computations inside this function before returning.
2. In case you use an unmanaged resource inside the loop, i may be very bad to exit without cleaning.

The code i posted is from a bigger class where i face the both cases, that's why i'm not exiting in the loop.
Cheers

RE: C# reading a text file - MavenGradle - Oct 4, 2019

(Oct 4, 2019 07:45 AM)max_int Wrote:  I agree with the idea of returning immediately  when the string is found.
Anyway, in some cases, it may not be the best option
1. you need to do some computations inside this function before returning.
2. In case you use an unmanaged resource inside the loop, i may be very bad to exit without cleaning.

The code i posted is from a bigger class where i face the both cases, that's why i'm not exiting in the loop.
Cheers

You have no reason not to return immediately inside the function that you shared with us, which by the way will not compile due to an incorrect return value and because the string.Contains method has NO OVERLOAD for a StringComparer. You're using a using statement which means the StreamReader will be disposed of correctly no matter how you look at it. If an exception is thrown at any point (including evaluating the return value) Dispose will still be called too. Even if this is part of a larger code base, what you're doing is still incredibly bad practice because it adds more steps in the chain which are simply unnecessary.

I agree that any resources should be disposed of properly because the .NET GC is not perfect, has been known to let certain things linger in memory etc. In such cases, you'd be better of using a using statement inside a using statement to make sure that the dispose method will be called correctly or dispose of it yourself in the right manner by calling the IDisposable.Dispose() method.