C# File Operations

[gangleader]

Hi,
I am working on a method which adds a new line in a text file.
The line should be of this format.
Line name (length 15, start position 0)
Project name (length 20, start position 0 + 15)
date (length 8, start position 0+15+20 )

For example i just took 3 fields, in real i have to deal with more than 10 fields
Length is the maximum length. If the length is less then it adds spaces. if the length is greater than than required length then it should erase that entire line.

Ex:
TestLineName TestProjectName 06172009 --- This is correct line

TestLineName TestProjectNameAgain --- this is incorrect as TestProjectNameAgain exceeds max limit. Now how can i remove only the second line?



I am able to create a new line when all conditions are fine but when there is any exception then I am not sure how to delete that line. Can any one help me please?

code:
int startPosition = 0
using (FileStream fs = new FileStream(saveToPath, FileMode.Append, FileAccess.Write))
{

if (Line_Name.Length > 15)
throw new Exception();
//and delete the current line... how to implement?
else
bytesToWrite = System.Text.ASCIIEncoding().GetBytes(Line_Name);

fs.Seek(startPosition , SeekOrigin.Begin);
fs.Write(bytesToWrite, 0, bytesToWrite.Length);


if (Project_name.Length > 20)
throw new Exception();
//and delete the current line... how to implement?
else
bytesToWrite = System.Text.ASCIIEncoding().GetBytes(Project_name);
fs.Seek(startPosition + 15, SeekOrigin.Begin);
fs.Write(bytesToWrite, 0, bytesToWrite.Length);

if (createDate.Length > 8)
throw new Exception();
//and delete the current line... how to implement?
else
bytesToWrite = System.Text.ASCIIEncoding().GetBytes(createDate);
fs.Seek(startPosition + 35, SeekOrigin.Begin);
fs.Write(bytesToWrite, 0, bytesToWrite.Length);

}


I am stuck at two things.
1. Not able to delete the current line
2. Is there any better way to do entire funtionality?

Please help me.
TIA

[vcstarter]

I think you approach the problem the wrong way. You have to use the stream class to write the file line by line then read it line by line then delete specific line that you want. The way you have it now is not the way to approach it. Try to use the following

using System.IO;

//then use the following classes to read and write the file line by line
StreamWriter outputFile;
StreamReader inputFile;

You may need to declare them different than the way I declared them above

[BigEd781]

I think you approach the problem the wrong way. You have to use the stream class to write the file line by line then read it line by line then delete specific line that you want. The way you have it now is not the way to approach it. Try to use the following

using System.IO;

//then use the following classes to read and write the file line by line
StreamWriter outputFile;
StreamReader inputFile;

You may need to declare them different than the way I declared them above

As far as I am aware, you cannot modify a file in arbitrary locations. You can append to a file, or you can read the file into memory, change it, and then replace the original completely.

[gangleader]

I think you approach the problem the wrong way. You have to use the stream class to write the file line by line then read it line by line then delete specific line that you want. The way you have it now is not the way to approach it. Try to use the following

using System.IO;

//then use the following classes to read and write the file line by line
StreamWriter outputFile;
StreamReader inputFile;

You may need to declare them different than the way I declared them above

I cannot use the StreamWriter i guess. Its not like writing entire line at a time. I have to write the text at specified location.

Line name (length 15, start position 0) --- I have start writing it at position 0
Project name (length 20, start position 0 + 15) -- for this i have to start writing it at position 15
date (length 8, start position 0+15+20 ) -- for this at position 35

For that im trying this way and iam able to write it correctly.

bytesToWrite = System.Text.ASCIIEncoding().GetBytes(createDate);
fs.Seek(startPosition + 35, SeekOrigin.Begin);
fs.Write(bytesToWrite, 0, bytesToWrite.Length);

[foamy]

try this approach:

1. read the entire file into memory. This can be done either with the StreamReader or the File.ReadAllLines method.
2. Modify the string(s) you need to
3. Write the entire file to the filesystem using either a StreamWriter or File.WriteAllLines...

(vcstarter has this one figured out, I'm just saying this to strengthen his/her point)

Some sample code might look like this:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;

namespace ModifyFile
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] file = File.ReadAllLines(@"C:\MyFile.txt");
            string lineName = "line name here";
            for(int i = 0; i < file.Length; i++)
            {
                file[i] = file[i].Insert(0, lineName.PadRight(15, ' '));
            }
            File.WriteAllLines(@"C:\MyFile.txt", file);
        }
    }
}

Edit: Oh, and BigEd781 said the same thing too

[Mutant_Fruit]

Just to reiterate what was already said, but in a slightly different way. You can't easily do it the way you're trying. You have to either:

A) Read the entire file into memory, zero the existing file by setting its length to '0', then validate each line before you write it back out.

or B) Read the file into memory line by line and after each line is validated to be correct, write it to a temporary file. When all lines have been processed, delete the original file and rename the temporary file to the correct name.