Exercise 10 (Week 11)- A first function template

SCIT-EIS-UOW
CSCI251/CSCI851 Advanced Programming

Laboratory Exercise 10 (Week 11)
Note that lab exercises marked with a * are effectively extension exercises.
1 Task One: Warm–up exercises
1. Why will the following fail to compile?
class B
{
public:
virtual void X() = 0;
};
class D : B
{
public:
virtual void X() {cout << "D object" << endl;}
};
int main()
{
B objB;
}
2. Why is the following class not very useful?
class X {
public:
virtual void x() final = 0;
};
3. Debug-A.cpp only has one problem, a missing constructor for CSL. Fix it!
4. * The file primes.cpp contains the code from slide 8 of S6b. This code calculates primes at compile
time, although not in the best of ways. Time how long compilation takes for a range of values of
LAST, which you can set by compiling as follows:
$ time CC -DLAST=10 primes.cpp
Choose sensible values of LAST to use and continue working on other activities while the program
is compiling. Graph the times taken, using something like Excel. A single compilation at a value
may not be a good reflection of the typical cost.
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2 Task Two: A first function template
Write code Symbolic.cpp that contains a function template to display a value preceded and succeeded by
n elements of a symbol x on a line, with a space on each side of the value. Write a main() function that
tests the function with char, int, double and string arguments. The output could be, for example,
*** 47 ***
000 39.25 000
aaaa Bob aaaa
What would a ADT X need in order to work with your function template? Use another appropriate
class that you have previously seen to test this.
3 Task Three: Follow the algorithm
Consider the function template and definitions below.
template <typename T>
T funcExp(T list[], int size){
int j;
T x = list[0];
T y = list[size-1];
for(j=1; j<(size-1)/2;j++){
if (x < list[j]) x = list[j];
if (y > list[size-1-j]) y = list[size-1-j];}
return (x+y); }
int list[8]={1,2,9,3,5,8,13,10};
string strlist[]={"one","fish","two","fish","red","fish","blue","fish"};
Determine the output of the following statement, firstly without implementing the code and then check
your solution by implementing it in funcExp.cpp.
cout << funcExp(list,8) << " :: " << funcExp(strlist,8) << endl;
4 Task Four: A class template
Write a class template Two<R,S> with the two parameterised types R and S. Write the class template and
a main() function with appropriate code to test the following functionality as you add it.
1. The class should have a constructor that takes one object of each type and uses those to set the
values in the object.
2. There should be a display function that outputs the object values.
3. There should be a function that attempts to add the two variables together.
What happens if you attempt to instantiate a template class based on this class template for types
where at least one of the operations doesn’t make sense.
5 * Task Five: A variadic function
Write a recursive variadic function to print out the number of arguments in the pack being passed in
each call to a display function, along with the argument being outputted at the time. This is a minor
modification of the code in the lecture notes set S6b.
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6 * Task Six: A little bit more
The file Bits-of-Memory contains three versions of the same class. Data elements that correspond to
Boolean states (0 or 1) are stored in three different ways. Firstly using an int to store each data element,
secondly using a bool to store each, and thirdly using a single bit to store each data element.
The advantage of using single bit fields is that of saving space. We can, more generally, use unsigned
x:y, where y is a positive integer, to indicate that we associate y bits with the variable x. You can also
do things like this ...
unsigned char b1 : 3, : 2, b2 : 6, b3 : 2;
to leave some of the bits empty.
There is more information at:
http://en.cppreference.com/w/cpp/language/bit_field
1. Explore the use of this.
2. How large does y need to be for one of the flags in DriverUsingBits before the size of the objects
of the class increases?
3. How large can y usefully be?
4. On Banshee each file has a permission string listed with it, tied to what users can do. So ...
$ ls -a
-rw------- 1 lukemc csstf 1336 Sep 18 13:13 Bits-of-Memory.cpp
-rw-rwxrw- 1 lukemc csstf 1340 Sep 18 12:53 Dog.cpp
...
The permission string is the -rw------- at the start. Ignoring the 1st dash, the next 3 correspond
to (r)ead, (w)rite, and e(x)ecute permissions for the owner (lukemc), the next 3 for the group (csstf),
and the last for everybody else. So in the listing above the owner can read and write Dog.cpp, the
group can read, write, and execute Dog.cpp, and everybody else can read and write Dog.cpp.
Write a bit based class to store, and interact with, permission strings.
c Luke McAven, SCIT-EIS-UOW, 2019.
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