For a couple of good examples, check out:
http://www.vsdotnet.be/blogs/tommer/2006/10/02/CreatingBarcodesOnTheFlyWithC.aspx
Is it possible to generate barcodes from a string using c#?
Yes, it is. There are quite a lot of frameworks that do it - either as a font or an image.
Is there any built-in classes for generating barcodes in asp.net?
No, but this c# project on github allows a string to be converted into an image (even multiple barcode types). All you need to do then is display the image in your application, just like any other image.
Is it possible to detect a barcode printer connected with a system?
Yes, in a WinForm application, for example, you could use System.Drawing.Printing.PrinterSettings.InstalledPrinters
.
to detect if you have printer installed then you may simply enumerate available printers using:
System.Drawing.Printing.PrinterSettings.InstalledPrinters
Yep. Of course it is possible. :-)
As far as I know there are two ways to generate bar codes:
In response to your updated question about detecting barcode printers:
I think a barcode printer will show up as a regular printer on your system. At least that is how the devices I have played with have worked.
This means that you can detect a specific barcode printer by enumerating the installed printers on the system and looking for the specified device, but in most cases I would suggest that you let the user specify the printer himself using either the standard print dialog or using a custom dialog.
Barcode fonts
exist in asp.net (IE web). You could draw barcode
text to an image and display that. This could be a similar implementation to a capcha
control.
For generating barcodes try http://www.codeproject.com/Articles/20823/Barcode-Image-Generation-Library
Allows saving to image with or without label and supports a number of formats.