Re: question about c-lang.c

Andrew Cagney
2002-09-12T21:44:43Z

> Today I happened to read c-lang.c:c_emit_char().
>
> Suppose a string contains the characters \0 (nul), `0' and finally `1'.
> (See appended source.)
>
> Now print this string:
>
> (gdb) p *c @ 4
> $2 = "\001"
>
> This output is ambiguous, as \001 has another meaning.

Isn't it simply wrong? A C parser would treat that as '\1'.

> I believe this is a problem for programs using MI. They can't
> correctly parse this output (should they want to).
>
>
> I've appended one possible fix. This isn't ideal since it also
> changes how char literals are printed. Perhaps that is acceptable?

How are char literals changed? Anyway, check this:

(gdb) cagney@b1$ gdb a.out
GNU gdb 4.18
Copyright 1998 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain
conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty" for details.
This GDB was configured as "i386-unknown-freebsd"...
(gdb) b main
Breakpoint 1 at 0x80483e3: file c.c, line 7.
(gdb) run
Starting program: /tmp/a.out

Breakpoint 1, main () at c.c:7
7 printf ("%s\n", c);
(gdb) print c
$1 = 0x8048407 ""
(gdb) print *c@4
$3 = "\00001"
(gdb)

So regardless you've got a regression! The patch is approved.

Can you also add to a testcase?

Andrew

> Tom
>
>
> #include <stdio.h>
>
> char *c = "\00001";
>
> int main ()
> {
> printf ("%s\n", c);
> return 0;
> }
>
>
> Index: ChangeLog
> from Tom Tromey <tromey@redhat.com>
>
> * c-lang.c (c_emit_char): Don't treat \0 specially.
>
> Index: c-lang.c
> ===================================================================
> RCS file: /cvs/src/src/gdb/c-lang.c,v
> retrieving revision 1.13
> diff -u -r1.13 c-lang.c
> --- c-lang.c 11 Jul 2002 13:50:49 -0000 1.13
> +++ c-lang.c 10 Sep 2002 23:26:06 -0000
> @@ -78,9 +78,6 @@
> case '\007':
> fputs_filtered ("\\a", stream);
> break;
> - case '\0':
> - fputs_filtered ("\\0", stream);
> - break;
> default:
> fprintf_filtered (stream, "\\%.3o", (unsigned int) c);
> break;
>