Re: array size 1 ? All headers

["Luiz Fernando N. Capitulino" <lcapitulino@terra.com.br>]

Em Tue, 20 Jul 2004 22:17:43 -0500
Eric Bambach <eric@cisu.net> screveu:

| >  The program:
| >
| >  char tst[1];
| >  tst[0]='g';
| >  tst[1]='r';
| >
| >  printf("%c %c\n", tst[0], tst[1]);
| >
| >  compiles and works here! but to be honest, I don't why. I can prove it is
| > an odd case, becase this also works (here):
| >
| >  char tst[1];
| >  tst[0]='g';
| >  tst[1]='r';
| >  tst[2]='z';
| >
| >  printf("%c %c %c\n", tst[0], tst[1], tst[2]);
| >
| > PS: GCC compiled.
| 
| 
| I think small overflows like this will work because arrays are allocated in 
| multiples of the word size for the artitecture. So char 
| ar[1];
| gets 4 bytes as does char ar[2], char ar[3] and char ar[4].
| char ar[5] will get 8 bytes. So  with ar[1] and ar[5] you can stuff up to 3 
| more charaters until you overwrite critical parts of the stack. Its not an 
| error per se, because the space is given to the array, but its a horrible 
| thing to do in practice.

 Oh yeah, the best pratice is to write right code. :-)


-- 
Luiz Fernando