c++ - std::pair and class destructors

Possible
Duplicate:
href="https://stackoverflow.com/questions/4172722/what-is-the-rule-of-three">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            my_class> my_map;

 my_map.insert( std::make_pair            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!

itemprop="text">

class="normal">Answer

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 href="https://stackoverflow.com/questions/4172722/what-is-the-rule-of-three">Rule of
three

In C++11 also
look at href="https://stackoverflow.com/questions/3106110/can-someone-please-explain-move-semantics-to-me">move
constructor if you are worried about the
efficiency.