Memory allocation and C compatibility

The standard way of allocating memory in C involves a `malloc' function that allocates memory and a `free' function that frees it. Portability constraints on `malloc' and `free' preclude using the length information those functions must store to determine how many C objects to destroy. This means that C implementations must be able to store the length somewhere else. Because auxiliary storage can only be used for arrays, programmers must state whether they are freeing scalars or arrays, but not how many elements there are in the array. Combining these rules constrains the design of C memory allocation facilities. Fortunately, these constraints are not hard to live with in practice, and is possible to implement in ways that are portable and useful.