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* [Bug c/17253] New: Inconsistency in reading array indexes @ 2004-08-31 19:50 vanveghel at home dot nl 2004-08-31 20:03 ` [Bug c/17253] " falk at debian dot org ` (3 more replies) 0 siblings, 4 replies; 5+ messages in thread From: vanveghel at home dot nl @ 2004-08-31 19:50 UTC (permalink / raw) To: gcc-bugs Consider the following two snippets: -- snip snip -- #include <stdio.h> #include <string.h> int main (void) { char test[5][5]; int j = 3; memset (&test, ' ', 5 * 5); test[j][j++] = '!'; printf ("test[3][3] = %c\ntest[4][3] = %c\n", test[3][3], test[4][3]); return 0; } -- snip snip -- And: -- snip snip -- #include <stdio.h> #include <string.h> int main (void) { char test[5][5]; int j = 3; memset (&test, ' ', 5 * 5); test[(j == 4) ? 4 : 3][j++] = '!'; printf ("test[3][3] = %c\ntest[4][3] = %c\n", test[3][3], test[4][3]); return 0; } -- snip snip -- Running both these snippets produces the following results with GCC 3.3.4 running on Debian GNU/Linux Unstable (x86): $ ./test test[3][3] = test[4][3] = ! $ ./test2 test[3][3] = ! test[4][3] = $ It seems that j++ is evaluated first only in the second case, making the statement in the first bracket evaluate to 4. This may be a result of 'undefined behavior' caused by sequence points, and indeed, GCC does issue a warning ("warning: operation on `j' may be undefined"), but it does seem like something that can at least be improved. Kind Regards, Jasper -- Summary: Inconsistency in reading array indexes Product: gcc Version: 3.3.4 Status: UNCONFIRMED Severity: normal Priority: P2 Component: c AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: vanveghel at home dot nl CC: gcc-bugs at gcc dot gnu dot org GCC build triplet: 3.3.4 GCC host triplet: 3.3.4 GCC target triplet: 3.3.4 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17253 ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c/17253] Inconsistency in reading array indexes 2004-08-31 19:50 [Bug c/17253] New: Inconsistency in reading array indexes vanveghel at home dot nl @ 2004-08-31 20:03 ` falk at debian dot org 2004-08-31 20:44 ` pinskia at gcc dot gnu dot org ` (2 subsequent siblings) 3 siblings, 0 replies; 5+ messages in thread From: falk at debian dot org @ 2004-08-31 20:03 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From falk at debian dot org 2004-08-31 20:03 ------- Uhm, the code is invalid, and the compiler warns about it. What could possibly be improved? -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17253 ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c/17253] Inconsistency in reading array indexes 2004-08-31 19:50 [Bug c/17253] New: Inconsistency in reading array indexes vanveghel at home dot nl 2004-08-31 20:03 ` [Bug c/17253] " falk at debian dot org @ 2004-08-31 20:44 ` pinskia at gcc dot gnu dot org 2004-08-31 20:46 ` bangerth at dealii dot org 2004-08-31 20:46 ` bangerth at dealii dot org 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu dot org @ 2004-08-31 20:44 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From pinskia at gcc dot gnu dot org 2004-08-31 20:44 ------- No there is nothing which can be improved except maybe for you fixing your code not be use undefined code. -- What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution| |INVALID http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17253 ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c/17253] Inconsistency in reading array indexes 2004-08-31 19:50 [Bug c/17253] New: Inconsistency in reading array indexes vanveghel at home dot nl 2004-08-31 20:03 ` [Bug c/17253] " falk at debian dot org 2004-08-31 20:44 ` pinskia at gcc dot gnu dot org @ 2004-08-31 20:46 ` bangerth at dealii dot org 2004-08-31 20:46 ` bangerth at dealii dot org 3 siblings, 0 replies; 5+ messages in thread From: bangerth at dealii dot org @ 2004-08-31 20:46 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From bangerth at dealii dot org 2004-08-31 20:46 ------- Duplicate of PR 11751. *** This bug has been marked as a duplicate of 11751 *** -- What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution| |DUPLICATE http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17253 ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c/17253] Inconsistency in reading array indexes 2004-08-31 19:50 [Bug c/17253] New: Inconsistency in reading array indexes vanveghel at home dot nl ` (2 preceding siblings ...) 2004-08-31 20:46 ` bangerth at dealii dot org @ 2004-08-31 20:46 ` bangerth at dealii dot org 3 siblings, 0 replies; 5+ messages in thread From: bangerth at dealii dot org @ 2004-08-31 20:46 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From bangerth at dealii dot org 2004-08-31 20:46 ------- Indeed. What more than a warning do you want? -- What |Removed |Added ---------------------------------------------------------------------------- Status|RESOLVED |UNCONFIRMED Resolution|INVALID | http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17253 ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2004-08-31 20:46 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2004-08-31 19:50 [Bug c/17253] New: Inconsistency in reading array indexes vanveghel at home dot nl 2004-08-31 20:03 ` [Bug c/17253] " falk at debian dot org 2004-08-31 20:44 ` pinskia at gcc dot gnu dot org 2004-08-31 20:46 ` bangerth at dealii dot org 2004-08-31 20:46 ` bangerth at dealii dot org
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