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.NET Forum / .NET Framework / New Users / January 2008Char datatype does some hocus pocus
Dim B As Byte = 150 Dim C As Char C = Convert.ToChar(B) B = Asc(C) And the value of B is 63 Why?  SignatureArne Garvander Certified Geek Professional Data Dude > Dim B As Byte = 150 > Dim C As Char > C = Convert.ToChar(B) > B = Asc(C) > And the value of B is 63 > Why? Convert.ToChar will use Unicode - so you end up with Unicode 150. That character (the control character "start of guarded area") almost certainly isn't in your ANSI character encoding. Moral: avoid Asc and Chr, which implicitly use ANSI. Use the Encoding class instead, where you explicitly specify the encoding. SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk > Dim B As Byte = 150 > Dim C As Char > C = Convert.ToChar(B) > B = Asc(C) > And the value of B is 63 > Why? Because 150 isn't a valid ASCII value (ASCII is 0 to 127). 63 is the ASCII code for a question mark ('?'), and that's what Asc is returning when you pass it a character that doesn't have a valid ASCII code. Pete > > Dim B As Byte = 150 > > Dim C As Char [quoted text clipped - 6 lines] > ASCII code for a question mark ('?'), and that's what Asc is returning > when you pass it a character that doesn't have a valid ASCII code. To be strict about it, Asc is misnamed - it returns 63 when you pass it a character which doesn't have a valid *ANSI* code for the default ANSI code page on your system. Unfortunately there's a bad history of assuming that ASCII==ANSI (and that ANSI is a specific encoding, rather than a whole collection of them). <shudders> SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk > To be strict about it, Asc is misnamed - it returns 63 when you pass it > a character which doesn't have a valid *ANSI* code for the default ANSI > code page on your system. Unfortunately there's a bad history of > assuming that ASCII==ANSI (and that ANSI is a specific encoding, rather > than a whole collection of them). Ah, I see. I changed the code to use Chr(B) instead of Convert.ToChar() and it does actually convert to the appropriate Unicode character ('\u2013' in this case). I made the error of assuming that the call to Convert.ToChar() was doing something that the OP expected, but now I see that it expects Unicode values and so passing what's an ANSI value does actually allow Asc() to return the right thing. I had assumed from the name that Asc() would return only ASCII values, but looking at the doc page I see that it does return characters from the ANSI range, just as you said. I guess the moral is either to follow your original advice (use an explicit Encoding for conversion), or in VB if you are just using the default ANSI encoding then just use the appropriate function, Chr(), instead of passing an ANSI value to a function that expects Unicode (Convert.ToChar()). Of course, yet another fix is to just stop using ANSI and switch over to Unicode. :) Then if you want to specify that character by value, use 2013 instead of 150 and everything works fine. Pete > [...] I made the error of assuming that the call to Convert.ToChar() > was doing something that the OP expected, but now I see that it expects > Unicode values and so passing what's an ANSI value does actually allow > Asc() to return the right thing. I wrote that, and I'm not even sure what it means. Obviously, passing an ANSI value to a method that expects a Unicode value isn't going to do the right thing. Not then, not later. If you pass the correct Unicode value to Convert.ToChar(), you can later get the expected ANSI value from Asc(). The Unicode will be converted to ANSI for you. But only if you start with the correct, corresponding Unicode character in the first place. But this is a VB-specific thing. I agree that if you're writing .NET code, and doing character encoding conversions, that using the actual Encoding class is the appropriate solution. It makes it much more clear what's going on, and isn't tied to a specific character encoding (the code can be easily changed or generalized to use a different encoding than ANSI). Of course, it's not clear from the OP's post that he wanted or expected _any_ conversion. In which case, it's really just a matter of avoiding the .NET methods in the first place, and sticking to the VB functions that deal only in ANSI. Anyway, sorry for writing that confusing sentence. I wish I know what thought I was trying to express at the time. :) Pete If I try to put non-ANSI data into a string then I am screwed. Before I got my current contract, someone started to put EBCDIC data into strings. No it will take to much effort to clean it up. SignatureArne Garvander Certified Geek Professional Data Dude > > [...] I made the error of assuming that the call to Convert.ToChar() > > was doing something that the OP expected, but now I see that it expects [quoted text clipped - 26 lines] > > Pete
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