If there exists any memory block allocated using malloc() / calloc() / realloc() which has not been free()'d, at the end of the program, they would be free()'d automatically.

One can easily do it with keeping a linked list and using atexit(), but, can it be added to the standard?

A general question, will anything, any feature, which is "easy" to implement in pure C, like array knowing its own length or pascal strings, NOT be allowed to be in C standard, even if it is widely used, maybe almost everywhere?