If free() knows the length of my array, why can't I ask for it in my own code?

Question

I know that it\'s a common convention to pass the length of dynamically allocated arrays to functions that manipulate them:

void initializeAndFree(int* anArr         


        

Answer 1

You can't get it because the C committee did not require that in the standard.

If you are willing to write some non-portable code, you may have luck with:

*((size_t *)ptr - 1)

or maybe:

*((size_t *)ptr - 2)

But whether that works will depend on exactly where the implementation of malloc you are using stores that data.