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When an exception is thrown while executing a tt(new[]) expression, what will
happen? In this section we'll show that tt(new[]) is
hi(new[]: and exceptions)hi(exception: and new[]) exception safe even when
only some of the objects were properly constructed.
To begin, tt(new[]) might throw while trying to allocate the required
memory. In this case a ti(bad_alloc) is thrown and we don't leak as nothing
was allocated.
Having allocated the required memory the class's default constructor is going
to be used for each of the objects in turn. At some point a constructor might
throw. What happens next is defined by the bf(C++) standard: the destructors
of the already constructed objects are called and the memory allocated for
the objects themselves is returned to the common pool. Assuming that the
failing constructor offers the basic guarantee tt(new[]) is therefore
exception safe even if a constructor may throw.
The following example illustrates this behavior. A request to allocate and
initialize five objects is made, but after constructing two objects
construction fails by throwing an exception. The output shows that the
destructors of properly constructed objects are called and that the allocated
em(substrate memory) is properly returned:
verbinclude(-a examples/new.cc)
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