std::pair and class destructors

Possible Duplicate:
What is The Rule of Three?

How exactly does std::pair call destructors for its components? I am trying to add instances of a class to an std::map , but I am getting errors regarding the destructor of my class.

I have narrowed down my question/problem to the following extremely simple example.

Below, my_class merely creates an int array at construction, and deletes it at destruction. Somehow I am getting a "double delete" error:

//my_class.h
class my_class {
  public:
    int an_int;
    int *array;

    //constructors:
    my_class()
    {
      array = new int[2];
    }
    my_class(int new_int) : an_int(new_int)
    {
      array = new int[2];
    }

    //destructor:
    ~my_class()
    {
      delete[] array;
    }
};  //end of my_class

Meanwhile, over in main.cpp...

//main.cpp
int main(int argc, char* argv[])
{
  std::map<int, my_class>   my_map;

  my_map.insert( std::make_pair<int, my_class> (1, my_class(71) ) );

  return 0;
} // end main

Compilation goes fine, but this generates the following runtime error:

*** glibc detected *** ./experimental_code: double free or corruption (fasttop):

Or, with valgrind:

==15258== Invalid free() / delete / delete[] / realloc()
==15258==    at 0x40249D7: operator delete[](void*) (vg_replace_malloc.c:490)
==15258==    by 0x8048B99: main (my_class.h:38)
==15258==  Address 0x42d6028 is 0 bytes inside a block of size 8 free'd
==15258==    at 0x40249D7: operator delete[](void*) (vg_replace_malloc.c:490)
==15258==    by 0x8048B91: main (my_class.h:38)

(line numbers are off because I cut out comments and stuff)

I must be missing something about std::pair ...?

Thanks to all in advance!

---

When you add my_class to stl containers the copy constructor is called. As you don't define one it does a memberwise copy and two my_class objects are created that point to the same int array, When these are deleted the same int array might be deleted twice

Please take a look at Rule of three

In C++11 also look at move constructor if you are worried about the efficiency.

---

Your class violates the rule of three by defining a destructor without a copy constructor and an assignment operator. Once you define these, your code should run OK: STL containers rely heavily on these, so you should ask yourself if you've implemented all three every time you use a class as a template argument for an STL container.

---

你必须定义一个合适的拷贝构造函数，因为你的类的拷贝通过指针的复制实例共享同一个数组。

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