Bug#232430: libc6: strtof is completelly broken, garbage is returned

[Daniel Jacobowitz <dan@debian.org>]

On Thu, Feb 12, 2004 at 06:44:25PM +0100, Roberto Gordo Saez wrote:
> Package: libc6
> Version: 2.3.2.ds1-11
> Severity: important
> 
> The function strtof does not work at all, it always returns garbage.
> Many programs are silently broken by this bug. This small
> example will return a random number, without using rand :-)
> 
>     #include <stdlib.h>
>     #include <stdio.h>
>     #include <stddef.h>
> 
>     int main (void)
>     {
>         printf ("%f\n", strtof ("5E+2", NULL));
>         return 0;
>     }
> 
> Actually, the value returned by strtof seems to come from a pointer
> freely walking through the stack; declaring a new, unused variable
> sometimes makes a different value returned, like in this case:

drow@nevyn:~% gcc -g -o stof stof.c -Wall
stof.c: In function `main':
stof.c:7: warning: implicit declaration of function `strtof'
stof.c:7: warning: double format, different type arg (arg 2)

Always, always use compiler warnings when looking at a problem like
this one.

According to stdlib.h strtof is only available in C99 mode.  If I add
-std=c99 the program works.  If you add -D_GNU_SOURCE, it probably will
work then also.

At most the man page needs a note.  It does already say:
CONFORMING TO
       ANSI C describes strtod, C99 describes the other two functions.


-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer