EECS 281 MIDTERM QUESTIONS WITH CORRECT ANSWERS

EECS 281 MIDTERM QUESTIONS WITH CORRECT
ANSWERS



What is memory ownership for a container? - ans-
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When a container owns a value, only that container can modify the value. A drawback of thi
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s is it takes a long time to copy containers like this. When a container has pointers, either the
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container or other objects pointing to the same thing can modify, which can be unsafe. This
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can be used for shared data. When a container owns a reference to a value, it doesn't own t
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he value. You cannot delete by reference. The value must be initialized but cannot be assig
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ned to. xz xz




student answer: xz xz




Memory ownership of a container refers to how controlled the interface is to the data held wi
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thin the container. There are different degrees of ownership ranging from no control (as in t
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he case of references) to a lot of control (which is the default from within the container). A co
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ntainer class can control how much access objects outside the class can have over the ele
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ments of the container (hence the class has a public interface for other objects).
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A container composed of values can completely restrict or give complete access to the ele
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ments (the former being impractical and the latter being close to what vector does) but in eit
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her situation the container class mutates the data.
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A container composed of pointers however is a different story. Because they contain pointe
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rs, the container only protects the location data (the pointer data) but it cannot protect or con
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trol the interface to the data stores at the addresses. Thus, the container does not have total
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control over the relevant data. Hypothetically, an object outside the container can make edi
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ts to the data.xz xz xz




What are some disadvantages of arrays? - ans-
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when many insertions are needed, we need to move everything over EVERY time we insert
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a number.
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One disadvantage of an array is that there are no bound checks so you increase the change
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of illegally accessing memory (causing a seg fault) or you need O(1) complexity overhead li
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ke a size variable to maintain bound checks.
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Why do you need a const and non-const version of some operators?
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What should non=const op[ ] return ? - ans-xz xz xz xz xz xz xz xzxz




Read and write. In some cases, the compiler knows it can speed some things up if it knows i
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t never has to make any changes. Non const operator returns the object, which can be modi
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fied. xz

, You would need both const and non-
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const version of operations because you would want to be as safe as possible. One good ru
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le for C++ programming from the book "Effective C+
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+" highlights that you should make every variable you don't manipulate a const variable to p
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rotect any data you can. Having methods return const makes your operation more resilient t
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o potential bugs (like accidently mutating data in a container when you didn't want to).
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how many destructor calls (min, max) can be invoked by
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operator delete xz xz




operator delete[ ] - ans- xz xz xz xzxz




A destructor should have only one call to delete for each new allocation to the heap and one
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call to delete[] for each new[] allocation to the heap.
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Why would you use a pointer-based copying algorithm? - ans-Pointer-
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based algorithm works with both random access and sequential access (ex: will work with b
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oth a linked list and a vector).Random access would not work with a linked list, just a vector.
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You would use a pointer- xz xz xz xz




based copying algorithm when the objects are very large and it would be costly to copy or w
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hen you don't necessarily know the end of a container so you can use a nullptr as the null ter
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minator. This is the idea behind vector.end() iterator which is an iterator that points one past
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the end of a vector.
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Are C++ strings null-terminated? - ans-no
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Give two examples of off-by-one bugs - ans-
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accessing one off the end of the array when comparing i <= SIZE. Assigning one off the end
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of the array with arr[i] = arr[i + 1] when i = size - 1.
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How do I set up a two-dim array class? - ans-setup an array of int pointers:
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const int ** arr = new int * [R]; xz xz xz xz xz xz xz xz xz




The array is a collection of pointers, which is currently not looking at anything
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Perform an amortized complexity analysis of an automatically resizable container with a do
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ubling policy - ans- xz xz xzxz




When a call to add an element places the element one passed the end, the container will re
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size to twice it's size. In amortized complexity analysis, we find the cost per operation over a
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sequence of operations. In the worst case of the container reaching it's limit, the complexity
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of the nth addition would be O(n). However, the next n-
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1 calls to add an element will have a O(1) complexity. So we have n + n(1) = 2n => O(n) com
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plexity. O(n) / n = O(1) amortized complexity. xz xz xz xz xz xz xz




Discuss pros and cons of pointers and references when implementing container classes. -
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ans-Pointers vs references in container classes.
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