When inside a constructor a multidimensional array is declared whose size
depends on a variable, e.g. int n = 5; int a[n][n];, address calculation for
accessing the array elements is wrong. Example code:
--- snip ---
int result;
class A {
public:
A();
};
void remember(int i) {
result = i;
}
void test() {
int n = 5;
int a[n][n];
a[0][4] = 42;
a[4][0] = 43;
remember(a[0][4]); // a[0][4] still is 42
}
A::A() {
int n = 5;
int a[n][n];
a[0][4] = 42;
a[4][0] = 43; // overwrites a[0][4]!
remember(a[0][4]); // a[0][4] is 43
}
int main(int argc, char** argv) {
A* object = new A();
return result;
}
--- snip ---
In the above code, the constructor will set result to 43. The identical code of
test() will set result to 42.
The assembler code of test() and the constructor differs slightly: in test(), n
is stored in %ecx, moved to %eax for some computation, and is later moved to
%eax a second time. In the constructor, however, n is moved to %eax directly and
later, where test() would movl %ecx, %eax, the constructor does movl 0, %eax
instead.
$gcc --version
gcc (GCC) 3.3.5 (Debian 1:3.3.5-5)
--
Summary: Dynamically sized static multidimensional array access
in constructor uses wrong address
Product: gcc
Version: 3.3.5
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: lathander at gmx dot de
CC: gcc-bugs at gcc dot gnu dot org
GCC build triplet: i486-linux ?
GCC host triplet: i486-linux ?
GCC target triplet: i486-linux ?
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19254
