http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57853
Bug ID: 57853
Summary: pointer arithmetic on arrays
Product: gcc
Version: 4.6.3
Status: UNCONFIRMED
Severity: critical
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: brodhow at all2easy dot net
This C code:
#include <stdio.h>
int main() {
char *arr [2][3]={{"as","df","ce"},{"me","yu","we"}};
char *arr2 = NULL;
puts(*arr[0]);//works fine
puts(*arr[1]);//works fine
printf("%c\n",*++arr[0][0]);//works fine and prints s
printf("%s\n", *arr[0]);
int i = 0, j = 0;
for (i=0; i<2; ++i)
for (j=0; j<3; ++j)
printf("%s ", arr[i][j]);
printf("\n");
}
outputs:
as
me
s
s
s df ce me yu we
where the 'a' in "as" (arr[0]) is being wiped out! After the
"printf("%c\n",*++arr[0][0]);" statement! Or, the string arr's head is being
reassigned to the new value after the "*++arr[0][0]" operation which is 's'!
the output should be:
as
me
s
as
as df ce me yu we
where the 'a' in "as" is present, afterwards!
The pointer arithmetic here to get 's' to output is producing this side effect
of wiping out the 'a' in "as", arr[0]. Is "*++arr[0][0]" valid for getting 's'
in "as"? If so, then this side effect is happening! For real in any legacy C
code with similar syntax! When said C code is recompiled by the current gcc
compiler! Note that g++ does the same thing here too, on this code.
