Part 6 - Templates, Containers, Vectors, Iterators, STL Algorithms

Question 1

What does

template <class></class>

above a method indicate?

Answer 1

T is a type parameter that can be instantiated with any type

So at compile time a version of the method will be generated for each type that uses it

Question 2

Write a template version of the swap function

Answer 2

template <class></class>

void swap(T& a, T& b) {

T tmp = a;

a = b;

b = tmp;

}

Question 3

Write a method that prints a pair where each member of the pair can be of a different type

Answer 3

template <class></class>

void printPair(const S& s, const T& t) {

cout << s << “, “ << t << endl;

}

Question 4

What is a template class?

Answer 4

A class where one of the members can be of any type

Question 5

Write the header for a class Pair that has two members of any type, a constructor and two methods getFirst and getSecond

Answer 5

template <class></class>

class Pair {

private:

S first;

T second;

public:

Pair(S s, T t) : first(s), second(t){};

S getFirst() const { return first; }

T getSecond() const { return second; }

};

Question 6

Why must a template class be written as one file?

Answer 6

Writing a separate file wont work because the type names S or T or whatever wont be in scope in the .cpp file. So has to be written in the header.

Question 7

what is a container in STL?

Answer 7

A template class in the STL that contains a collection of objects and algorithms

Question 8

What are the 3 sequence containers (that store sequential data) in the STL?

Answer 8

vector

deque

list

Question 9

What are container adapters?

Answer 9

Containers that do not provide full functionality because their design means some operations may not apply

Question 10

What are the 3 container adapters?

Answer 10

stack

queue

priority_queue

Question 11

What are the 4 associative containers?

Answer 11

set

multiset

map

multimap

Question 12

What does the no-arg constructor do for all STL containers?

copy constructor?

Answer 12

initialise the collection to be empty

initialise a collection to contain copies of the objects in the existing collection

Question 13

What 4 functions do ALL classes in STL have? What do they do?

Answer 13

size(), empty(), max_size() and swap()

size() returns number of items in collection

empty() returns true if 0 items else false

max_size() returns max possible size for container

swap() takes reference to another container of same type and swaps the contents of the two containers

Question 14

What does the clear() function do with containers?

Answer 14

Sets the collection to be empty

Question 15

What does the vector class do? What header is needed?

Answer 15

Parametrised Array with range checking

<vector></vector>

Question 16

what will vector<char> v3(10, 'x'); do?</char>

Answer 16

Create a vector v3 that contains 10 x’s

Question 17

Why use .at over [] for vectors?

Answer 17

.at has range checking

Question 18

what does vector.reserve(100) do?

Answer 18

Increases the capacity of vector to 100

Question 19

If a vector is resize() ed to a smaller size than its current size what happens?

Answer 19

Elements after the resized size get deleted

Question 20

What are the 3 types of iterator?

Answer 20

unidirectional (++), bidirectional (++ and –) and random access (full poitner arithmetic)

Question 21

Write a function to iterate over a vector<int> using a const iterator</int>

Answer 21

void testFunc(const vector<int>&amp; v) {</int>

vector<int>::const_iterator it;</int>

for (it = v.begin(); it != v.end(); it++) {

cout << *it << endl;

}

}

Question 22

Write a function to iterate over a vector backwards using a const iterator

Answer 22

void printBackwards(const vector& v) {

vector::const_reverse_iterator it;

for (it = v.rbegin(); it != v.rend(); it++) {

cout << *it << endl;

}

}

Question 23

How does the erase function work with STL containers?

Answer 23

takes a non const iterator and removes the item it is pointing to

Question 24

Write a function to remove the first instance of 0 in a vector<int></int>

Answer 24

void removeFirst0(vector<int>&amp; v) {</int>

vector<int>::iterator it;</int>

for (it = v.begin(); it != v.end(); it++) {

if (*it == 0) {v.erase(it); return;}

}

}

Question 25

Why can one iterator not be used in conjunction with erase() to remove more than one instance of a given thing?

Answer 25

The iterator value after erase() is called is undefined

Question 26

What does the two arg version of erase() do?

Answer 26

Removes all items in a range

e. g.
v. erase(v.begin(), v.begin+3); would remove the first 3 elements

Question 27

How do typedefs work?

Answer 27

typedef theactualtype alias;

e.g.

typedef vector<int>::const_reverse_iterator CRI;</int>

then you could use

CRI it = v.begin();