C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  7 bit char          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message TK Guest Posted: Sat Feb 28, 2004 9:24 pm    Post subject: 7 bit char I have encountered a very strange bug. I am using a variable defined as: char ch; If I assigned a character like 'Ö' (ascii 153) with a statement like: ch = 'Ö'; It gets the value -103. It's as if char now is a signed datatype, which it has never been before. I am developing in MS DevStudio 6.0. Is there a setting somewhere that could have been changed? I have never seen this before, and I have coded for about 10 years. I have even run the code I have problems with now before without this problem (most recently just a few days ago). Can anything else I have installed screwed up this? When researching the problem on the web, I did find some references to a file called limits.h that deals with this, and it does exist on my computer, but I have not added any referencees to it my code. Any help is much appreciated, Thanks, TK Back to top Alf P. Steinbach Guest Posted: Sat Feb 28, 2004 9:35 pm    Post subject: Re: 7 bit char * [email]t_karlsson72 (AT) hotmail (DOT) com[/email] (TK) schriebt: Quote: I have encountered a very strange bug. I am using a variable defined as: char ch; If I assigned a character like 'Ö' (ascii 153) with a statement like: Incorrect. The ASCII code does not define code points above 127. Also, 'Ö' is not an ASCII character. Possibly you mean ISO 8859-1? Quote: ch = 'Ö'; It gets the value -103. It's as if char now is a signed datatype, Yep, and from 153 - 256 = -103 you can deduce that this implementation's char type is most probably eight bits. Hence the subject line about "7 bit char" is most probably incorrect, and in any event misleading. Quote: which it has never been before. Incorrect. Neither C nor C++ has ever defined whether 'char' is signed or unsigned. That's up to the implementation. On the other hand, 'signed char' is signed, and 'unsigned char' is unsigned. Many compilers have some means of forcing 'char' to be signed or unsigned. Quote: I am developing in MS DevStudio 6.0. Is there a setting somewhere that could have been changed? I have never seen this before, and I have coded for about 10 years. Incorrect. MSVC 6.0 isn't 10 years old. Also, the default in MSVC 6.0 was, as I recall, that 'char' mapped to 'signed char'. Back to top Alberto Barbati Guest Posted: Sun Feb 29, 2004 1:47 am    Post subject: Re: 7 bit char TK wrote: Quote: It's as if char now is a signed datatype, which it has never been before. I am developing in MS DevStudio 6.0. Is there a setting somewhere that could have been changed? I have never seen this before, and I have coded for about 10 years. Which compiler did you use before? As far as I remember, char has always been a signed datatype by default on Microsoft compilers as well as many other C/C++ compilers I happened to work with in the last 17 years. BTW, you can tell MSVC to make char unsigned by using the /J option. Regards, Alberto Barbati Back to top Ivan Vecerina Guest Posted: Sun Feb 29, 2004 11:38 am    Post subject: Re: 7 bit char "TK" <t_karlsson72 (AT) hotmail (DOT) com> wrote Quote: ... It's as if char now is a signed datatype, which it has never been before. I am developing in MS DevStudio 6.0. Is there a setting somewhere that could have been changed? Note that, according to the C++ standard, the integral type 'char' may be either signed or unsigned. Unlike other integral types (short, int, long), 'char', 'signed char' and 'unsigned char' are tree distinct types. Rather than changing compiler settings, it would be wiser to write code that can work with both signed and unsigned variants of 'char': replace 'char' with 'unsigned char', or cast values to 'unsigned char' when needed. Regards, Ivan -- http://ivan.vecerina.com/contact/?subject=NG_POST <- e-mail contact form Back to top Mike Wahler Guest Posted: Sun Feb 29, 2004 8:42 pm    Post subject: Re: 7 bit char "TK" <t_karlsson72 (AT) hotmail (DOT) com> wrote Quote: Re: 7 bit char I have encountered a very strange bug. I am using a variable defined as: char ch; If I assigned a character like 'Ö' (ascii 153) with a statement like: ch = 'Ö'; 1. Please explain how you can represent the number 153 with only seven bits. 2. The ASCII character set only defines character encodings with values from zero through 127. Quote: It gets the value -103. You're seeing implementation-specific behavior. Quote: It's as if char now is a signed datatype, It can be, and often is. Quote: which it has never been before. The language does not specify whether type 'char' is signed or unsigned. It must be one or the other, but which is left to the implementation. Quote: I am developing in MS DevStudio 6.0. All Microsoft compilers I've ever used for the last two decades or so, *all* have type 'char' which is signed. (but all offered an 'option' to change it to unsigned if desired). Quote: Is there a setting somewhere that could have been changed? Yes. See above. Quote: I have never seen this before, and I have coded for about 10 years. In 10 years, you never noticed that MS compilers' type 'char' is signed by default? Quote: I have even run the code I have problems with now before without this problem (most recently just a few days ago). A common situation with C is the existence of 'problems' often for a long time, that don't visibly manifest themselves. Quote: Can anything else I have installed screwed up this? That's a possiblity. Quote: When researching the problem on the web, I did find some references to a file called limits.h that deals with this, The standard header <limits.h> defines the characteristics of many language entities whose exact specifications are left to the implementation (but subject to certain restrictions and requirements). E.g. the macro 'CHAR_BIT' tells how many bits comprise a character (the language mandates that this value be at least eight, but allows it to be greater). Quote: and it does exist on my computer, but I have not added any referencees to it my code. You don't need the header unless you need to refer to any symbols it defines. Quote: Any help is much appreciated, Try changing the default 'signedness' of char (see the documentation to learn how), or change your type in your source code to 'unsigned char' specifically. In any event, is it really necessary to be concerned with the actual numerical values of your characters? Why not specify them with character (or string) literals, e.g. 'A', "ABC". -Mike Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         C++Talk.NET Forum Index -> C++ language (comp.lang.c++) All times are GMT Page 1 of 1   Jump to: Select a forum C/C++----------------C LanguageC Language (Moderated)C++ Language (Moderated)C++ language (comp.lang.c++)C++ language, library and standards Non-English C/C++ Newsgroups----------------C++ (German)C++ (French)  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.