C++ Array bound exception on overflow - "cout" and no "cout"

#include <iostream>

int main()
{
  int array1[10] = {0};
  char* array2[10] = {'\0'};

  for (int i = 0; i <= 100; i++)
  {
    std::cout << arr开发者_如何转开发ay1[i];   // This does not crash 
    //std::cout << array2[i]; // This crashes
    array1[i]; // Wont crash here
    array2[i]; // nor here, Why? because there is no cout??
  }
  return 0;
}

Ok so for the people answering here, i know i deliberately made an overflow for the arrays. So why does the program crash on "cout", but not otherwise??

Thanks!

---

Given that the value is unused, it is probably optimized away by the compiler and never really retrieved at run time.

---

EDIT: In response to the changed version of the question, the reason it crashes for array2 but not array1 is that (at least under MSVC) the operator<< for char* tries to get the length of the pointed-to string and ends up dereferencing a NULL pointer. You get the same behaviour if you do:

std::cout << (char*)NULL;

The crash in this case is not caused by the out-of-bounds access, but by a null pointer dereference.

---

Despite that, further to what @UncleZeiv said, you can tell what code's actually doing by looking at the disassembly output from your compiler. For instance, on VC++ 2008, I get:

        std::cout<<array1[i]; //--> This crashes
00B2151E  mov         esi,esp 
00B21520  mov         eax,dword ptr [i] 
00B21523  mov         ecx,dword ptr array1[eax*4] 
00B21527  push        ecx  
00B21528  mov         ecx,dword ptr [__imp_std::cout (0B2A334h)] 
00B2152E  call        dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (0B2A318h)] 
00B21534  cmp         esi,esp 
00B21536  call        @ILT+405(__RTC_CheckEsp) (0B2119Ah) 
        std::cout<<array2[i]; //--> So does this
00B2153B  mov         eax,dword ptr [i] 
00B2153E  mov         ecx,dword ptr array2[eax*4] 
00B21542  push        ecx  
00B21543  mov         edx,dword ptr [__imp_std::cout (0B2A334h)] 
00B21549  push        edx  
00B2154A  call        std::operator<<<std::char_traits<char> > (0B2114Fh) 
00B2154F  add         esp,8 
        array1[i]; // But not this one
        array2[i]; // nor this, Why?

In other words, the compiler is not outputting any instructions when you're not doing anything with array1[i] and array2[i] (the two instructions are no-ops), so the program doesn't crash even though you're theoretically referencing something beyond the bounds of the array and invoking undefined behaviour.