Effects: If it is possible to fit size bytes of storage aligned by alignment into the buffer pointed to by ptr with length space, the function updates ptr to point to the first possible address of such storage and decreases space by the number of bytes used for alignment. Otherwise, the function does nothing.
Returns: A null pointer if the requested aligned buffer would not fit into the available space, otherwise the adjusted value of ptr.
[ Note: The function updates its ptr and space arguments so that it can be called repeatedly with possibly different alignment and size arguments for the same buffer. — end note ]