C++ STL. Standard Template Library. A library of all important
data structure classes and tools thereof.
e.g. STL containers: vector, deque, list
container adapters: stack, queue, priority_queue
Associative containers: set, multiset, map, multimap, bitset
We begin with a vector.
A vector looks like an array, but more supple.
array a[5]
Once declared, an array has fixed size. But a vector could be
resized via its resize function.
vector <int> marks(20);
//marks is a vector initialized to size 20
vector <double> attributes(6);
//attributes is a vector initialized to size 6
Here is a typical program where a vector looks like an array.
#include <iostream>
#include <vector>
using namespace std;
main()
{
vector <double> v(5);
for (int i=0; i<5; i++)
cin>>v[i];
cout<<endl<<"Heights of the group of size: ";
cout<<v.size()<<endl;
for (int i=0; i<5; i++)
cout<<v[i]<<" ";
cout<<endl;
}
Now see what we can do with a vector.
#include <iostream>
#include <vector>
using namespace std;
main()
{
vector <double> v; // no initialization
int count; //find out how many in the group
cin>>count; //user specified group size
v.resize(count); //configure vector of size count
for (int i=0; i<v.size(); i++)
cin>>v[i];
cout<<endl<<"Heights of the group of size: ";
cout<<v.size()<<endl;
for (int i=0; i<v.size(); i++)
cout<<v[i]<<" ";
cout<<endl;
}
On p. 478, selected vector operations are indicated.
One of the methods for a vector is a push_back.
v.push_back(k) //appends k at the end of v. size of v increases by 1
Example.
#include <iostream>
#include <vector>
using namespace std;
main()
{
vector <double> v; // no initialization
int count; //find out how many in the group
cin>>count; //user specified group size
v.resize(count);
cout<<"Current capacity of the vector heights: ";
cout<<v.capacity()<<endl;
for (int i=0; i<v.size(); i++)
cin>>v[i];
cout<<endl<<"Heights of the group of size: ";
cout<<v.size()<<endl;
for (int i=0; i<v.size(); i++)
cout<<v[i]<<" ";
cout<<endl;
cout<<endl<<endl;
cout<<"Current capacity of the vector heights: ";
cout<<v.capacity()<<endl;
v.push_back(7.5);
v.push_back(7.3);
v.push_back(7.4);
for (int i=0; i<v.size(); i++)
cout<<v[i]<<" ";
cout<<endl;
}
OUTPUT
Current capacity of the vector heights: 7
Heights of the group of size: 7
5.4 6 5.9 7.8 7.2 6 5.11
Current capacity of the vector heights: 7
5.4 6 5.9 7.8 7.2 6 5.11 7.5 7.3 7.4
Another example.
#include <iostream>
#include <vector>
using namespace std;
main()
{
int i;
vector <int> v;
v.reserve(3); //make room for 3 units
v.push_back(50); //append 50
cout<<"Size now: "<<v.size()<<" Capacity now: "<<v.capacity();
cout<<endl;
for (i=0; i<v.size(); i++)
cout<<v[i]<<" ";
cout<<endl;
v.resize(5); // increase size to 5
cout<<"Size now: "<<v.size()<<" Capacity now: "<<v.capacity();
cout<<endl;
v.push_back(40);
for (i=0; i<v.size(); i++)
cout<<v[i]<<" ";
cout<<endl;
v.reserve(1); // ignores it since the capacity is bigger already
for (i=0; i<v.size(); i++)
cout<<v[i]<<" ";
cout<<endl;
v.resize(3);
cout<<"Size now: "<<v.size()<<" Capacity now: "<<v.capacity();
cout<<endl;
v.resize(8,2); //fill it up with 2
for (i=0; i<v.size(); i++)
cout<<v[i]<<" ";
cout<<endl;
cout<<"Size now: "<<v.size()<<" Capacity now: "<<v.capacity();
cout<<endl;
}
OUTPUT
Size now: 1 Capacity now: 3
50
Size now: 5 Capacity now: 5
50 0 0 0 0 40
50 0 0 0 0 40
Size now: 3 Capacity now: 10
50 0 0 2 2 2 2 2
Size now: 8 Capacity now: 10
Iterators. A way to access elements of a container.
It’s an object that allows a programmer to traverse through all
elements of a collection (list, queue, map, table, …) regardless of
how the collection is implemented.
To work with an iterator for a specific class, we need to define an
iterator for that class. Similarly, the concept of reverse iterator.
e.g. vector<int> :: iterator it; //it is an iterator for an int vector
vector <int> :: reverse_iterator rit;
(see p. 487)
Example.
#include <iostream>
#include <vector>
using namespace std;
main()
{
vector <double> a;
vector <double> :: iterator it;
vector <double> :: reverse_iterator rit;
a.push_back(5.7);
a.push_back(6.3);
a.push_back(4.9);
a.push_back(5.8);
a.push_back(8.6);
for(it=a.begin(); it != a.end(); it++)
cout<<(*it)<<" "; // Iterate forward
cout<<endl;
cout<<endl;
for (rit=a.rbegin(); rit <a.rend(); rit++)
cout<<*rit<<" "; // Iterate reverse
cout<<endl;
}
OUTPUT
5.7 6.3 4.9 5.8 8.6
8.6 5.8 4.9 6.3 5.7
Why Iterator?
• counting loops do not always work well for every
data structure, iterator provides a consistent way to
iterate data structure of all kinds.
• Iterators enforce additional constraints: elements
can be skipped, already visited element is not
visited again, …
• An iterator may allow the container object to be
modified.
C++ STL (Standard Template Library) provides all kinds
of iterators: Forward iterators, bi-directional iterators,
random access iterators.
Example.
#include <iostream>
#include <list>
using namespace std;
main()
{
list <int> mylist;
list <int> :: iterator it;
list <int> :: reverse_iterator rit;
int i;
for (i=0; i<5; i++)
mylist.push_back(i+10);
cout<<"About mylist: "<<endl;
cout<<endl;
cout<<"Current size: "<<mylist.size()<<endl;
cout<<"Content: "<<endl;
for(rit = mylist.rbegin(); rit != mylist.rend(); rit++)
cout<<"**** "<<*rit<<endl;
cout<<endl;
}
OUTPUT
About mylist:
Current size: 5
Content:
**** 14
**** 13
**** 12
**** 11
**** 10
@@@@@ 10
@@@@@ 11
@@@@@ 12
@@@@@ 13
@@@@@ 14
Another example. This time with a map. A map is a list of pairs
like
(‘A’
(‘B’
→
→
132) The character A is mapped to 132
8) ‘B’ is mapped to 8
#include <iostream>
#include <map>
using namespace std;
main()
{
map <char,int> mymap;
map <char,int> :: iterator it;
mymap['A'] = 132;
mymap['B'] = 8;
mymap['C'] = 26;
mymap['D'] = 87;
cout<<"About mymap: "<<endl;
cout<<"Size: "<<mymap.size()<<endl;
for (it = mymap.begin(); it != mymap.end(); it++)
cout<<it->first<<" , "<<it->second<<endl;
cout<<endl;
}
OUTPUT
About mymap:
Size: 4
A , 132
B,8
C , 26
D , 87
Another example. Swapping maps.
#include <iostream>
#include <map>
using namespace std;
main()
{
map <char,int> mymap;
map <char,int> yourmap;
map <char,int> :: iterator it;
mymap['A'] = 132;
mymap['B'] = 8;
mymap['C'] = 26;
mymap['D'] = 87;
yourmap['X'] = 12;
yourmap['Y'] = 46;
yourmap['Z'] = 19;
cout<<"About mymap: "<<endl;
cout<<"Size: "<<mymap.size()<<endl;
for (it = mymap.begin(); it != mymap.end(); it++)
cout<<it->first<<" , "<<it->second<<endl;
cout<<endl;
cout<<"About yourmap: "<<endl;
cout<<"Size: "<<yourmap.size()<<endl;
for (it = yourmap.begin(); it != yourmap.end(); it++)
cout<<it->first<<" , "<<it->second<<endl;
cout<<endl;
// swap two maps;
mymap.swap(yourmap);
cout<<"About mymap: "<<endl;
cout<<"Size: "<<mymap.size()<<endl;
for (it = mymap.begin(); it != mymap.end(); it++)
cout<<it->first<<" , "<<it->second<<endl;
cout<<endl;
cout<<endl;
cout<<"About yourmap: "<<endl;
cout<<"Size: "<<yourmap.size()<<endl;
for (it = yourmap.begin(); it != yourmap.end(); it++)
cout<<it->first<<" , "<<it->second<<endl;
cout<<endl;
}
OUTPUT
About mymap:
Size: 4
A , 132
B,8
C , 26
D , 87
About yourmap:
Size: 3
X , 12
Y , 46
Z , 19
About mymap:
Size: 3
X , 12
Y , 46
Z , 19
About yourmap:
Size: 4
A , 132
B,8
C , 26
D , 87