Re: Two questions on arrays with size defined by variables

On Mon, 10 Feb 2025 02:44:26 +0100
Opus <ifonly@youknew.org> wrote:

On 09/02/2025 19:19, Michael S wrote:

On Sun, 9 Feb 2025 18:46:44 +0100
Janis Papanagnou <janis_papanagnou+ng@hotmail.com> wrote:
 

wrong! - assignment to 'a[99]' produced also no compiler
complaints, 

 
gcc produces warning in this case, but only at optimization level
of 2 or higher. 

 
Which version of gcc?

14.1

My test code is:

void bar(char*[]);
int foo(void)
{
  int n = 10;
  char *a[n];
  bar(a);
  a[99] = "42";
  return a[3][2];
}

Tried with gcc 14.2 (x86-64) with -Wall -O3 (or -O2, same), it
doesn't give any warning whatsoever. (And yes, same with clang.)
 

May be, in your test arr[] is not used later, so compiler silently
optimizes away all accesses?

Cppcheck does spot it properly though:
 
error: Array 'arr[5]' accessed at index 99, which is out of bounds.
[arrayIndexOutOfBounds]
   arr[99] = "foobar";
 
I highly recommend using Cppcheck as a static analyzer (at the bare
minimum, there are better out there). Compilers are pretty basic in
terms of static analysis.