What does valgrind's "still reachable" message mean?

When I check my programs with valgrind for memory leaks I usually get a "still reachable" result, even if there is no memory leak. An example valgrind output:

HEAP SUMMARY:

    in use at exit: 72,704 bytes in 1 blocks

   total heap usage: 3 allocs, 2 frees, 74,752 bytes allocated

72,704 bytes in 1 blocks are still reachable in loss record 1 of 1

…

LEAK SUMMARY:

   definitely lost: 0 bytes in 0 blocks

   indirectly lost: 0 bytes in 0 blocks

   possibly lost: 0 bytes in 0 blocks

   still reachable: 72,704 bytes in 1 blocks

On valgrind's doc it says: "still reachable" means your program is probably ok -- it didn't free some memory it could have. This is quite common and often reasonable.

I wrote a simple program:

#include <iostream>

int main() {

    return 0;

}

After I compile and check it with valgrind I get "still reachable". If I comment out the #include line, I don't get "still reachable". I have to research a little bit more.