Tools.h++ Manual

104011 Tandem Computers Incorporated 17-15
17
is used to calculate the number of bytes necessary to store an object using
RWFile . This is useful for classes RWFileManager and RWBTreeOnDisk
which require space to be allocated for an object before it can be stored.
Writing a version of binaryStoreSize() is usually very straightforward.
Just follow the pattern set by saveGuts(RWFile&) , except that instead of
saving member data, add up their sizes. The only real difference is a syntactic
one: instead of l-shift operators, you use member functions and sizeof() :
• For primitives, use sizeof() ;
• For objects that inherit from RWCollectable , use member function
RWspace RWCollectable::recursiveStoreSize() ;
• For other objects, use member function binaryStoreSize() .
Here’s a sample definition for class Bus :
Persisting custom collections
Class RWCollection has versions of saveGuts() and restoreGuts() built
into it that are sufficient for most collection classes.
RWCollection::saveGuts() works by repeatedly calling
RWvostream& operator<<(RWvostream&, const
RWCollectable&);
for each item in the collection. Similarly, RWCollection::restoreGuts()
works by repeatedly calling
RWspace Bus::binaryStoreSize() const
{
RWspace count = RWCollectable::binaryStoreSize() +
customers_.recursiveStoreSize() +
sizeof(busNumber_) +
driver_.binaryStoreSize();
if (passengers_)
count += passengers_->recursiveStoreSize();
return count;
}