🚀 go-pugleaf

I have just spent a long time tracking down a mysterious bug (the
heap-trashing variety of bug) in my program caused by a syntactic trap
in C++.  The troubling thing about this trap is that none of the unix
compilers I tried (gcc-2.7.2, Sun SC3.0.1, HP-UX cfront 3.0.3) issued
a warning about the mistake, even on the highest warning level.  Only
Visual C++4.0 observed that there might be a problem.  Here is an
example of the trap.  This program asks the user how many asterisks,
and then prints out that many asterisks.

#include <iostream.h>
int main() {
  cout << " How many *'s? ";
  int sz; cin >> sz;
  char* a = new char(sz + 1); // bug is here, but syntax is legal.
  for (int i = 0; i < sz; i++)
    a[i] = '*';
  a[sz] = 0;
  cout << a << endl;
  delete[] a;
  return 0;
}

(Does everyone see the error?  I did not, even after staring at my
code for a long time.  The point is that the marked statement is an
unintended cast from int to char because I used () instead of [].)

I would like to make a plea to the compiler-writers who read this
group: please issue warnings for syntactic trouble spots!  Implicit
type conversion probably creates other traps that I haven't thought
of.  C++ programmers like me need help from the compiler to navigate
the traps!

-- Steve Vavasis (vavasis@cs.cornell.edu)
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