Ridiculous Runtime Errors

Question

Write programs that produce crazy, obscure, ridiculous, or just plain nutty runtime errors. Obfuscation and golfitude (shortness) not required.

• solutions that look like they should work fine are better.
• solutions that look like they should break one way but break another are better.
• solutions that are nondeterministic are better as long as they are reproducible sometimes.
• solutions with long distance between error cause and manifestation are better.
• bonus points for producing errors that should be impossible.
• bonus points for errors that crash the runtime (like making python segment fault) or operating system. *

The unit of score shall be upvotes.

Addendum 1

Compiler misbehaviors are fine too.

Answer 1

The obligatory PHP one (which still hasn't been fixed as of 5.4):

<?::

Outputs:

Parse error: syntax error, unexpected T_PAAMAYIM_NEKUDOTAYIM on line 1

Whaa?

Answer 2

C(++)

If compile-time errors count here's one (assuming a file named "crash.c").

#include "crash.c"

int main(){ return 0; }

It fills the screen with this upon compilation (have Ctrl-C ready)

                 from crash.c:1,
                 from crash.c:1:
crash.c:3:1: error: redefinition of ‘main’
crash.c:3:1: note: previous definition of ‘main’ was here
In file included from crash.c:1:0,
                 from crash.c:1,
                 from crash.c:1,

Another snippet which compiles perfectly well (no warnings under -Wall and illustrates the beautiful type safety of C </s>

#include <stdio.h>
int i;

int main(){
  sprintf(NULL, "%s", (char *) (void *) (1/i));
  return 0;
}

Running it gives:

Floating point exception (core dumped)

Answer 3

I'll start:

#include <iostream>

using namespace std;

class A
{
public:
    A()
    {
    }

    void doSomethingDiabolical()
    {
        delete this;
    }

    virtual void breakHorribly()
    {
        cout << "still alive" << endl;
        doSomethingDiabolical();
        cout << "still alive" << endl;
    }
};

class B : public A
{
public:
    B() : A()
    {
    }

    void breakHorribly()
    {
        cout << "still alive" << endl;
        ((A *) this)->breakHorribly();
        cout << "still alive" << endl;
        doSomethingDiabolical();
        cout << "still alive" << endl;
        breakHorribly();
        cout << "dead" << endl;
    }
};

int main()
{
    jane();
}

void jane()
{
    cout << "still alive" << endl;
    A * o = new B;
    cout << "still alive" << endl;
    o->breakHorribly();
}

Any guesses why this program crashes? :D

See jane run: http://ideone.com/gtaZ3

Answer 4

How about compiler optimisation errors:

#include <stdio.h>

#define N 4

int main(void)
{
    int sum;
    int i;
    int arr[N];

    for (i = 0, sum = 0; i < N; i++, arr[i] = sum) {
        sum += arr[i];
    }
    printf("%d\n", sum);
    return 0;
}

This is specific to gcc >= 4.7. Compiles and runs fine with gcc -O0 -Wall. Compiles with gcc -O2 -Wall but results in an inf-loop.

Also note, how gcc does see the problem for smaller N, e.g. N = 3:

test.c:11:38: warning: array subscript is above array bounds [-Warray-bounds]
  for (i = 0, sum = 0; i < N; i++, arr[i] = sum) {
                                       ^
test.c:12:13: warning: 'arr[0]' is used uninitialized in this function [-Wuninitialized]
  sum += arr[i];
         ^

Btw, this has been taken from a bug report, I can't recall the bug number though.