File I/O - C# Discussion Boards

Re: function pointer in C#?

8-Jun-02 13:05

Yes, use \\ or put an @ before the start of the string (@"c:\sierra5\logs\").

James

Re: Use \ in string?

Brian Olej8-Jun-02 14:22

Brian Olej

8-Jun-02 14:22

Thank you

Re: Use \ in string?

Nick Parker8-Jun-02 18:43

Nick Parker

8-Jun-02 18:43

I know JTJ has already answered your question, but just in case you are interested Dr. GUI.NET has written a very good article on the string objects on MSDN. Here is the link.

Strings in the .NET Framework

Nick Parker

function pointer in C#?

Todd Smith7-Jun-02 14:36

Todd Smith

7-Jun-02 14:36

I want to create a Hashtable of strings and function pointers. How can I do that in C#/ASP.NET?

I'm just guessing here...

public string MyFunc(string instr)
{
    return instr + "blah";
}

Hashtable table = new Hashtable;
table.Add("myfunc", MyFunc);
string str = "blah";
string blahblah = (table["myfunc"])(str);

something like that? But I'm not sure how to store the function in the hashtable and how to retrieve it and use it.

Todd Smith

James T. Johnson7-Jun-02 14:59

Re: function pointer in C#?

7-Jun-02 14:59

In C# a function pointer is a delegate, so you'll be storing a delegate in the hashtable, and using the string as the key.

The delegate that can be used for MyFunc above would be:

public delegate string FunctionDelegate(string instr);

To add that to the hashtable you would do something like this.

Hashtable table = new Hashtable();

table["myfunc"] = new FunctionDelegate(MyFunc); (you could also use the Add method, but I prefer the array-like access).

Now to get it back out and use it;

// Remember the Hashtable works with objects, so you need to cast back
// to the original type
FunctionDelegate d = table["myfunc"] as FunctionDelegate;
 
// Call the method pointed to by the delegate
d(str);

I found understanding delegates the hardest part for me to learn; once you get it though you'll wonder why you didn't get it sooner Smile | :)

Good luck,

James

Todd Smith7-Jun-02 15:12

Todd Smith

7-Jun-02 15:12

Sweet. Now I'll be able to pull specific fields out of an ASP.NET form and convert the values before they get updated into the database.

public delegate string HoursToSecsCallbackType(string hours);
HoursToSecsCallbackType fp = new HoursToSecsCallbackType(Utils.HoursToSecs);
Hashtable table = new Hashtable();
table.Add("hours", fp);

string column = "hours";
TextBox textbox = (TextBox)objArgs.Item.FindControl(column);
if (table.ContainsKey(column))
{
    HoursToSecsCallbackType fp = (HoursToSecsCallbackType) table[column];
    textbox.Text = fp(textbox.Text);
}

Todd Smith

File I/O

7-Jun-02 13:36

Is there a good tutorial somewhere that includes basic file i/o?

I've found this:

// Create a text file C:\temp\mcb.txt
FileStream fs = new FileStream(@"c:\mcb.txt" , FileMode.OpenOrCreate, FileAccess.Write);
StreamWriter filef = new StreamWriter(fs);

// Write to the file using StreamWriter class
filef.BaseStream.Seek(0, SeekOrigin.End);
filef.Write(" File Write Operation Starts : ");
filef.WriteLine("{0} {1}", DateTime.Now.ToLongTimeString(),
DateTime.Now.ToLongDateString());
filef.WriteLine(" First Line : Data is first line \n");
filef.WriteLine(" This is next line in the text file. \n ");
filef.Flush();

but it doesn't work... I guess I'm looking for a basic explanation of what each one does and how to use them. A simple working example would be great, a tutorial would be great. Any help would be great Big Grin | :-D

Thanks for the help.

James T. Johnson7-Jun-02 14:03

7-Jun-02 14:03

Aside from missing a call to the Close() method on the stream that should work; what errors are you getting?

James

Nish Nishant7-Jun-02 14:11

Nish Nishant

7-Jun-02 14:11

http://www.codeproject.com/useritems/csfilestuff01.asp

Nish

Author of the romantic comedy

Summer Love and Some more Cricket [New Win]

Buy it, read it and admire me Smile | :)

8-Jun-02 9:30

This is the error I get(in runtime):

Application has generated an exception that could not be handled.

Then it gave me the process id and thread id (do you want those?).

Well anyways, here is my script. I an very new to C# so chances are I am making some stupid error where you wouldn't expect it (which is why I include the whole source).

using System; 
using System.IO;




class functions
{


	public static void writefile()
	{
		//Create a file 'nish.txt' in the current directory 
		FileStream fs = new FileStream("data.txt" , FileMode.Create, FileAccess.ReadWrite); 		
		
		//Now let's put some text into the file using the StreamWriter
		StreamWriter sw = new StreamWriter(fs); 		
		sw.WriteLine("Testing\n TESTING!\n yay!"); 

		sw.Flush();
	}	
		
}

class app
{

	public static void Main()
	{
	
		Console.WriteLine("Before writefile()");
		
		functions.writefile();
		
		Console.WriteLine("After writefile()");

	}



}

Humpo8-Jun-02 10:12

Humpo

8-Jun-02 10:12

I was able execute the code you gave with no errors, file was created and contained the expected text.

Try putting sw.Close(); after sw.Flush() and see if that has any effect.

Try debuging the project to identify which line causes the problem- use "step over"(F10) and "step into"(F11), found under the debug menu in Visual studio.

Sorry this isn't much help, maybe the problem lies somewhere else- OS related maybe?

James T. Johnson8-Jun-02 10:43

8-Jun-02 10:43

As Humpo said the code works fine here.

The error you stated doesn't help us, that error message is just saying some error happened. You should see something that says 'BlahBlahException'; that is the part we need to know so we know what error occured.

James

8-Jun-02 15:51

Sorry, using the command line compiler... thanks anyways for the help though.

I'll keep plowing through it.

8-Jun-02 16:23

Well i fixed it, Im not sure how- but i did.

Could you guys tell me how to move the file pointer around? My only real programming experience before this has been php. I know a open file has a internal pointer of some sort, i just dont know how to access it with c#.

Thanks

I'm confused, what exactly is C#

Humpo9-Jun-02 1:26

Humpo

9-Jun-02 1:26

Think this is what you are looking for

FileStream objects support random access to files using the Seek method. The Seek method allows the read/write position to be moved to any position within the file.

here's an example of using seek to move to the last 128 bytes of a file...

System.IO.FileStream istream = theFile.Open(FileMode.Open);
long fileLength = istream.Length;
if(fileLength > MP3_LENGTH)
{
	byte[] ba = new byte[MP3_LENGTH];
	istream.Seek(fileLength-MP3_LENGTH, SeekOrigin.Begin); 
	istream.Read(ba, 0 , MP3_LENGTH);
	GetFields(ba);
}

No doubt, as with all my code, there is a more efficient way Smile | :)

Nnamdi Onyeyiri7-Jun-02 12:58

Nnamdi Onyeyiri

7-Jun-02 12:58

I would like to know what C# is, its not c++, ive worked that out, looks to me like a cross between c++ and vb.

==================================================
Homepage: www.onyeyiri.co.uk
Email: theeclypse@hotmail.com
"I think Microsoft has invented A.I. My computer has a mind of its own!"

James T. Johnson7-Jun-02 14:08

7-Jun-02 14:08

I would classify it as a cross between C++, Java, and VB (C# borrows the VB construct for enumeration).

In the end though, language matters not because it is the .NET class libraries that do all of the work.

James

Nish Nishant7-Jun-02 14:13

Nish Nishant

7-Jun-02 14:13

While it was inherited from C++, inspired by Java/VB, it does have it's own nice little features I guess.

Nish

Author of the romantic comedy

Summer Love and Some more Cricket [New Win]

Buy it, read it and admire me Smile | :)

Christian Graus7-Jun-02 14:40

Christian Graus

7-Jun-02 14:40

It'sa basically a reworking of the J++ code, with some code from VB I'd guess and it's purpose in life is to annoy Scott McNeally.

Christian

I am completely intolerant of stupidity. Stupidity is, of course, anything that doesn't conform to my way of thinking. - Jamie Hale - 29/05/2002

James T. Johnson7-Jun-02 15:02