CS246 Midterm: CS 246 fall09ans
31 Jan 2019
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Department
Course
Professor
Final Exam Answers – CS 246 Fall 2009
Instructor: Peter Buhr
December 17, 2009
These are not the only answers that are acceptable, but these answers come from the notes or class
discussion.
1. (a) 3 marks A constructor is a special member used to perform initialization to ensure an object
is valid before use. It is called by the compiler immediately after object allocation.
(b) 2 marks Routine operators allow implicit conversions on both operands of an infix call.
(c) 4 marks Initialization involves a newly allocated object with undefined values. Assignment
involves an existing object that may contain previously computed values. The mechanism
used to implement each in C++ is the copy constructor and the assignment operator.
(d) 2 marks Ashallow-copy copies pointer values. A deep-copy copies the values referenced by
pointers (possibly recursively).
(e) 4 marks
1struct T2; // forward
struct T1 {
1 T2 *t2; // pointer, break cycle
1 T1(); // forward declaration
};
struct T2 {
T1 t1;
};
1 T1::T1() { t2 = new T2; } // can now see T2
T1 t1;
1struct T2; // forward
struct T1 {
1 T2 *t2; // pointer, break cycle
1 T1( T2 *t2 ) : t2( t2 ) {};
};
struct T2 {
T1 t1;
};
.5 T2 t2;
.5 T1 t1( t2 );
2. (a) 2 marks Type inheritance relaxes name equivalence by aliasing the derived name with its
base-type names.
(b) 1 mark routine pointers
(c) 5 marks
i. bp.f(); // Base::f
ii. bp.g(); // Base::g
iii. ((Derived &)bp).g(); // Derived::g
iv. bp.Base::h(); // Base::h
v. bp.h(); // Derived::h
(d) 3 marks Right picture
m2
m1
y
x
copy
y
x
direct routine pointer
y
x
VRT
m1
m2
m1
m2
indirect routine pointer
(e) 3 marks Adown cast is a dynamic check to determine the actual type an object pointed to by
apolymorphic pointer/reference.
1
Document Summary
Final exam answers cs 246 fall 2009. These are not the only answers that are acceptable, but these answers come from the notes or class discussion. 1. (a) 3 marks a constructor is a special member used to perform initialization to ensure an object is valid before use. It is called by the compiler immediately after object allocation. (b) 2 marks routine operators allow implicit conversions on both operands of an in x call. (c) 4 marks initialization involves a newly allocated object with unde ned values. Assignment involves an existing object that may contain previously computed values. The mechanism used to implement each in c++ is the copy constructor and the assignment operator. (d) 2 marks a shallow-copy copies pointer values. A deep-copy copies the values referenced by pointers (possibly recursively). (e) 4 marks. T1( t2 *t2 ) : t2( t2 ) {}; T1::t1() { t2 = new t2; } // can now see t2.
