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Date: Fri, 09 Jul 2010 04:57:42 +0000
From: Greg Chicares <gchicares AT sbcglobal DOT net>
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To: cygwin AT cygwin DOT com
Subject: Re: Interesting discovery in the C library that Cygwin uses
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On 2010-07-08 23:34Z, Gregg Levine wrote:
> I made this discovery whilst building the urjtag program from its SVN trunk:
> make[3]: Entering directory `/usr/local/urjtag/urjtag/trunk/urjtag/src/tap'
>  CC     tap.lo
>  CC     register.lo
>  CC     state.lo
>  CC     chain.lo
>  CC     detect.lo
> detect.c: In function `find_record':
> detect.c:89: warning: array subscript has type `char'

http://urjtag.svn.sourceforge.net/viewvc/urjtag/trunk/urjtag/src/tap/detect.c?annotate=1799
    char *p;
    ...
    while (*p && isspace (*p))

The problem is that 'char' can be signed, and a signed quantity can
be negative. But values passed to <ctype.h> functions like isspace()
have to be in the (nonnegative) range of an unsigned char (or be
equal to EOF); otherwise, the behavior is undefined. Consider using
    unsigned char *p;
instead of
    char *p;
in the example above.

Here's some discussion:

https://www.securecoding.cert.org/confluence/display/seccode/STR37-C.+Arguments+to+character+handling+functions+must+be+representable+as+an+unsigned+char

http://old.nabble.com/warnings-from-use-of-ctype.h-methods-td27865685.html

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