[Freeciv-Dev] Re: Compiler-warnings

[Raimar Falke <hawk@xxxxxxxxxxxxxxxxxxxxxxx>]

On Wed, Jan 24, 2001 at 11:05:26PM +0100, Stepan Roh wrote:
> 
> 
> On Wed, 24 Jan 2001, Tony Stuckey wrote:
> 
> >     It's probably a style error to use signed chars as array
> > subscripts.  Explicitly adding unsigned to silence these warnings should be
> > an acceptable patch, once that has been verified to not add any
> > out-of-range issues.
> >
> > int has_capability(const char *cap, const char *capstr)
> > {
> >   char *capstr_, *token, *next;
> >   int res=0, finished=0;
> >
> >   token = capstr_ = mystrdup(capstr);
> >   do {
> >     /* skip leading whitespace */
> >     while (isspace(*token))
> >       token++;
> >
> >     Compiling on a sparc running Solaris 8 using GCC, I get this style
> > of error on the while (isspace(*token)) line above, which does not have any
> > obvious array subscripting going on, though.
> 
> I finally recalled what's the point here (I had this problem last year
> when testing Allegro lib on IRIX). There are two kinds of libcs (which I
> know): traditional and GNU. Traditional libcs (such as those on Solaris
> and IRIX - both have their roots on AT&T Unix) have ctype.h functions
> #defined as (taken from Solaris's libc - (c) Sun Microsystems Inc.) :
> 
> #define isspace(c)      ((_ctype + 1)[c] & _S)
> 
> (they are inlined when using C++ with argument type of int, but not when
> using C).  This causes warning if c is of type signed char (which (for
> some reason I don't know - maybe tradition?)  char is defined as on every
> C compiler I know). And it should cause crash (in most cases) when using
> value of signed char outside <-1,127> - for example accented chars in some
> encodings.
> 
> GNU libc has this macro :
> 
> #define __isctype(c, type) \
>   (__ctype_b[(int) (c)] & (unsigned short int) type)
> 
> which recasts c to type int. And they also have __ctype_b starting at
> negative subscript values, so it won't crash with signed chars.

[ Negative subscript values? Is this a gnu extension? What are the
semantics?  What would you expect from:
-------
#include <stdio.h>

int main()
{
    int x,arr[10],y,i;

    for(i=0;i<10;i++)
        arr[i]=i;
    x=42;
    y=43;
    printf("[-1]=%d\n",arr[-1]);
    printf("[10]=%d\n",arr[10]);

    return 0;
}
-------

I expected 42 and 43 and missed. Now please add -O and test again. ]

So we can add a wrapper for is* or make the strings unsigned char *?!

        Raimar

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