The C standard doesn't actually require as much from the implementation as you might think. Pointer arithmetic and comparison is only defined for pointers into the same array object (including one past the end), so it's completely possible to implement C with bounds-checked fat pointers. The most painful requirement is probably that there is a sufficiently large integral type to represent pointers across round-trip casts. In portable CL that would require you to track all allocated objects with a unique identifier or implement your own heap.