Re: [gnugo-devel] cygwin sscanf problem in gtp.c

[Dave Denholm]

Trevor Morris <address@hidden> writes:

> Here's a test file that shows how gtp.c fails.
> In short, the " %s %n" construct isn't working as expected.  In the
> last sscanf, 1 is returned, but n is not set.  This causes very

Is the before %n intentional - it's saying match a string as %s,
then if it can match some whitespace, put the number of characers
consumed into %n. Since scanf stops as soon as the match fails,
it could satisfy the %s, but then if it fails to match the whitespace
it will return 1 without filling in the %n.

(Or maybe this is implementation dependent ?)

dd



> bad behavior in gtp.c (line 97, etc.) [specifically p += n].
> Is this specific to cygwin, or do other platforms have this problem
> too?
> 
> const char *db = "dragon_data black\n";
> const char *d1 = "dragon_data\n";
> 
> char command[1024];
> int n=-1,r;
> 
> dump(const char *s, char*command) {
>   printf("%d %d '%s' '%s'\n", r, n, command, s);
>   n = -1 ;
> }
> 
> 
> main() {
>   r = sscanf(d1, " %s%n", command, &n);
>   dump(d1, command);
>   r = sscanf(db, " %s%n", command, &n);
>   dump(db, command);
>   r = sscanf(d1, " %s%n", command, &n);
>   dump(d1, command);
> 
>   r = sscanf(d1, " %s %n", command, &n);
>   dump(d1, command);
>   r = sscanf(db, " %s %n", command, &n);
>   dump(db, command);
>   r = sscanf(d1, " %s %n", command, &n);
>   dump(d1, command);
> }
> 
> cygwin (gcc) output:
> 1 11 'dragon_data' 'dragon_data
> '
> 1 11 'dragon_data' 'dragon_data black
> '
> 1 11 'dragon_data' 'dragon_data
> '
> 1 -1 'dragon_data' 'dragon_data
> '
> 1 12 'dragon_data' 'dragon_data black
> '
> 1 -1 'dragon_data' 'dragon_data
> '
> 
> 
> VC output:
> 1 11 'dragon_data' 'dragon_data
> '
> 1 11 'dragon_data' 'dragon_data black
> '
> 1 11 'dragon_data' 'dragon_data
> '
> 1 12 'dragon_data' 'dragon_data
> '
> 1 12 'dragon_data' 'dragon_data black
> '
> 1 12 'dragon_data' 'dragon_data
> '
> 
> 
> 
> 
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dd
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