C++ STL (Standard Template Library) Tutorial and Examples

STL vector:

vector: Dynamic array of variables, struct or objects. Insert data at the end.

Simple example of storing STL strings in a vector. This example shows three methods of accessing the data within the vector:

#include <iostream>

            #include <vector>

            #include <string>

            

            using namespace std;

            

            main()

            {

            vector<string> SS;

            

            SS.push_back("The number is 10");

            SS.push_back("The number is 20");

            SS.push_back("The number is 30");

            

            cout << "Loop by index:" << endl;

            

            int ii;

            for(ii=0; ii < SS.size(); ii++)

            {

            cout << SS[ii] << endl;

            }

            

            cout << endl << "Constant Iterator:" << endl;

            

            vector<string>::const_iterator cii;

            for(cii=SS.begin(); cii!=SS.end(); cii++)

            {

            cout << *cii << endl;

            }

            

            cout << endl << "Reverse Iterator:" << endl;

            

            vector<string>::reverse_iterator rii;

            for(rii=SS.rbegin(); rii!=SS.rend(); ++rii)

            {

            cout << *rii << endl;

            }

            

            cout << endl << "Sample Output:" << endl;

            

            cout << SS.size() << endl;

            cout << SS[2] << endl;

            

            swap(SS[0], SS[2]);

            cout << SS[2] << endl;

            }

            

Compile: g++ exampleVector.cpp

Run: ./a.out

Output:

Loop by index:

The number is 10

The number is 20

The number is 30



Constant Iterator:

The number is 10

The number is 20

The number is 30



Reverse Iterator:

The number is 30

The number is 20

The number is 10



Sample Output:

3

The number is 30

The number is 10

---

Two / Three / Multi Dimensioned arrays using vector:

A two dimensional array is a vector of vectors. The vector contructor can initialize the length of the array and set the initial value.

Example of a vector of vectors to represent a two dimensional array:

#include <iostream>

            #include <vector>

            

            using namespace std;

            

            main()

            {

            // Declare size of two dimensional array and initialize.

            vector< vector<int> > vI2Matrix(3, vector<int>(2,0));    

            

            vI2Matrix[0][0] = 0;

            vI2Matrix[0][1] = 1;

            vI2Matrix[1][0] = 10;

            vI2Matrix[1][1] = 11;

            vI2Matrix[2][0] = 20;

            vI2Matrix[2][1] = 21;

            

            cout << "Loop by index:" << endl;

            

            int ii, jj;

            for(ii=0; ii < 3; ii++)

            {

            for(jj=0; jj < 2; jj++)

            {

            cout << vI2Matrix[ii][jj] << endl;

            }

            }

            }

            

Compile: g++ exampleVector2.cpp

Run: ./a.out

Loop by index:

0

1

10

11

20

21

---

A three dimensional vector would be declared as:

#include <iostream>

            #include <vector>

            

            using namespace std;

            

            main()

            {

            // Vector length of 3 initialized to 0

            vector<int> vI1Matrix(3,0);

            

            // Vector length of 4 initialized to hold another 

            // vector vI1Matrix which has been initialized to 0

            vector< vector<int> > vI2Matrix(4, vI1Matrix);

            

            // Vector of length 5 containing two dimensional vectors

            vector< vector< vector<int> > > vI3Matrix(5, vI2Matrix);

            

            ...

            

or declare all in one statement:

#include <iostream>

            #include <vector>

            

            using namespace std;

            

            main()

            {

            vector< vector< vector<int> > > vI3Matrix(2, vector< vector<int> > (3, vector<int>(4,0)) );

            

            for(int kk=0; kk<4; kk++)

            {

            for(int jj=0; jj<3; jj++)

            {

            for(int ii=0; ii<2; ii++)

            {

            cout << vI3Matrix[ii][jj][kk] << endl;

            }

            }

            }

            }

            

---

Using an iterator:

Example of iterators used with a two dimensional vector.

#include <iostream>

            #include <vector>

            

            using namespace std;

            

            main()

            {

            vector< vector<int> > vI2Matrix;    // Declare two dimensional array

            vector<int> A, B;

            vector< vector<int> >::iterator iter_ii;

            vector<int>::iterator                 iter_jj;

            

            A.push_back(10);

            A.push_back(20);

            A.push_back(30);

            B.push_back(100);

            B.push_back(200);

            B.push_back(300);

            

            vI2Matrix.push_back(A);

            vI2Matrix.push_back(B);

            

            cout << endl << "Using Iterator:" << endl;

            

            for(iter_ii=vI2Matrix.begin(); iter_ii!=vI2Matrix.end(); iter_ii++)

            {

            for(iter_jj=(*iter_ii).begin(); iter_jj!=(*iter_ii).end(); iter_jj++)

            {

            cout << *iter_jj << endl;

            }

            }

            }

            

Compile: g++ exampleVector2.cpp

Run: ./a.out

Using Iterator:

10

20

30

100

200

300

---

Constructor/Declaration:

Method/operator	Description
vector<T> v;	Vector declaration of data type "T".
vector<T> v(size_type n);	Declaration of vector containing type "T" and of size "n" (quantity).
vector<T> v(size_type n,const T& t);	Declaration of vector containing type "T", of size "n" (quantity) containing value "t". Declaration: vector(size_type n, const T& t)
vector<T> v(begin_iterator,end_iterator);	Copy of Vector of data type "T" and range begin_iterator to end_iterator. Declaration: template vector(InputIterator, InputIterator)

Size methods/operators:

Method/operator	Description
empty()	Returns bool (true/false). True if empty. Declaration: bool empty() const
size()	Number of elements of vector. Declaration: size_type size() const
resize(n, t=T())	Adjust by adding or deleting elements of vector so that its size is "n". Declaration: void resize(n, t = T())
capacity()	Max number of elements of vector before reallocation. Declaration: size_type capacity() const
reserve(size_t n)	Max number of elements of vector set to "n" before reallocation. Declaration: void reserve(size_t)
max_size()	Max number of elements of vector possible. Declaration: size_type max_size() const

Note: size_type is an unsigned integer.

Other methods/operators:

Method/operator	Description
erase() clear()	Erase all elements of vector. Declaration: void clear()
erase(iterator) erase(begin_iterator,end_iterator)	Erase element of vector. Returns iterator to next element. Erase element range of vector. Returns iterator to next element. Declarations: iterator erase(iterator pos) iterator erase(iterator first, iterator last)
= Example: X=Y()	Assign/copy entire contents of one vector into another. Declaration: vector& operator=(const vector&)
<	Comparison of one vector to another. Declaration: bool operator<(const vector&, const vector&)
==	Returns bool. True if every element is equal. Declaration: bool operator==(const vector&, const vector&)
at(index) v[index]	Element of vector. Left and Right value assignment: v.at(i)=e; and e=v.at(i); Declaration: reference operator[](size_type n)
front() v[0]	First element of vector. (Left and Right value assignment.) Declaration: reference front()
back()	Last element of vector. (Left and Right value assignment.) Declaration: reference back()
push_back(const T& value)	Add element to end of vector. Declaration: void push_back(const T&)
pop_back()	Remove element from end of vector. Declaration: void pop_back()
assign(size_type n,const T& t)	Assign first n elements a value "t".
assign(begin_iterator,end_iterator)	Replace data in range defined by iterators. Declaration:
insert(iterator, const T& t)	Insert at element "iterator", element of value "t". Declaration: iterator insert(iterator pos, const T& x)
insert(iterator pos, size_type n, const T& x)	Starting before element "pos", insert first n elements of value "x". Declaration: void insert(iterator pos, size_type n, const T& x)
insert(iterator pos, begin_iterator,end_iterator)	Starting before element "pos", insert range begin_iterator to end_iterator. Declaration: void insert(iterator pos, InputIterator f, InputIterator l)
swap(vector& v2)	Swap contents of two vectors. Declaration: void swap(vector&)

Iterator methods/operators:

Method/operator	Description
begin()	Return iterator to first element of vector. Declaration: const_iterator begin() const
end()	Return iterator to last element of vector. Declaration: const_iterator end() const
rbegin()	Return iterator to first element of vector (reverse order). Declaration: const_reverse_iterator rbegin() const
rend()	Return iterator to last element of vector (reverse order). Declaration: const_reverse_iterator rend() const
++	Increment iterator.
--	Decrement iterator.

---

Vector Links:

• SGI: vector - Detail of all vector member functions and operators available.
• Also see Boost ptr_vector - used to hold vector of pointers.

---

STL list:

list: Linked list of variables, struct or objects. Insert/remove anywhere.

Two examples are given:

1. The first STL example is for data type int
2. The second for a list of class instances.

They are used to show a simple example and a more complex real world application.

1. Lets start with a simple example of a program using STL for a linked list:

// Standard Template Library example

            

            #include <iostream>

            #include <list>

            using namespace std;

            

            // Simple example uses type int

            

            main()

            {

            list<int> L;

            L.push_back(0);              // Insert a new element at the end

            L.push_front(0);             // Insert a new element at the beginning

            L.insert(++L.begin(),2);     // Insert "2" before position of first argument

            // (Place before second argument)

            L.push_back(5);

            L.push_back(6);

            

            list<int>::iterator i;

            

            for(i=L.begin(); i != L.end(); ++i) cout << *i << " ";

            cout << endl;

            return 0;

            }

            

            

            

Compile: g++ example1.cpp

Run: ./a.out

Output: 0 2 0 5 6

[Potential Pitfall]: In Red Hat Linux versions 7.x one could omit the "using namespace std;" statement. Use of this statement is good programming practice and is required in Red Hat 8.0.

[Potential Pitfall]: Red Hat 8.0 requires the reference to "#include <iostream>". Red Hat versions 7.x used "#include <iostream.h>".

---

2. The STL tutorials and texts seem to give simple examples which do not apply to the real world. The following example is for a doubly linked list. Since we are using a class and we are not using defined built-in C++ types we have included the following:

• To make this example more complete, a copy constructor has been included although the compiler will generate a member-wise one automatically if needed. This has the same functionality as the assignment operator (=).
• The assignment (=) operator must be specified so that sort routines can assign a new order to the members of the list.
• The "less than" (<) operator must be specified so that sort routines can determine if one class instance is "less than" another.
• The "equals to" (==) operator must be specified so that sort routines can determine if one class instance is "equals to" another.

// Standard Template Library example using a class.

            

            #include <iostream>

            #include <list>

            using namespace std;

            

            // The List STL template requires overloading operators =, == and <.

            

            class AAA

            {

            friend ostream &operator<<(ostream &, const AAA &);

            

            public:

            int x;

            int y;

            float z;

            

            AAA();

            AAA(const AAA &);

            ~AAA(){};

            AAA &operator=(const AAA &rhs);

            int operator==(const AAA &rhs) const;

            int operator<(const AAA &rhs) const;

            };

            

            AAA::AAA()   // Constructor

            {

            x = 0;

            y = 0;

            z = 0;

            }

            

            AAA::AAA(const AAA &copyin)   // Copy constructor to handle pass by value.

            {                             

            x = copyin.x;

            y = copyin.y;

            z = copyin.z;

            }

            

            ostream &operator<<(ostream &output, const AAA &aaa)

            {

            output << aaa.x << ' ' << aaa.y << ' ' << aaa.z << endl;

            return output;

            }

            

            AAA& AAA::operator=(const AAA &rhs)

            {

            this->x = rhs.x;

            this->y = rhs.y;

            this->z = rhs.z;

            return *this;

            }

            

            int AAA::operator==(const AAA &rhs) const

            {

            if( this->x != rhs.x) return 0;

            if( this->y != rhs.y) return 0;

            if( this->z != rhs.z) return 0;

            return 1;

            }

            

            // This function is required for built-in STL list functions like sort

            int AAA::operator<(const AAA &rhs) const

            {

            if( this->x == rhs.x && this->y == rhs.y && this->z < rhs.z) return 1;

            if( this->x == rhs.x && this->y < rhs.y) return 1;

            if( this->x < rhs.x ) return 1;

            return 0;

            }

            

            main()

            {

            list<AAA> L;

            AAA Ablob ;

            

            Ablob.x=7;

            Ablob.y=2;

            Ablob.z=4.2355;

            L.push_back(Ablob);  // Insert a new element at the end

            

            Ablob.x=5;

            L.push_back(Ablob);  // Object passed by value. Uses default member-wise

            // copy constructor

            Ablob.z=3.2355;

            L.push_back(Ablob); 

            

            Ablob.x=3;

            Ablob.y=7;

            Ablob.z=7.2355;

            L.push_back(Ablob); 

            

            list<AAA>::iterator i;

            

            for(i=L.begin(); i != L.end(); ++i) cout << (*i).x << " "; // print member

            cout << endl;      

            for(i=L.begin(); i != L.end(); ++i) cout << *i << " "; // print all

            cout << endl;

            

            cout << "Sorted: " << endl;

            L.sort();

            for(i=L.begin(); i != L.end(); ++i) cout << *i << " "; // print all

            cout << endl;

            

            return 0;

            }

            

            

Output:

7 5 5 3 

7 2 4.2355

5 2 4.2355

5 2 3.2355

3 7 7.2355



Sorted:

3 7 7.2355

5 2 3.2355

5 2 4.2355

7 2 4.2355

---

List Links:

• SGI: list - Detail of all "list" member functions and operators available.
• Boost ptr_list and STL list of pointers - YoLinux Tutorial
• Also see Boost ptr_list - used to hold list of pointers.

---

STL vector vs list function comparison:

Function	vector	list
constructor	yes	yes
destructor	yes	yes
empty()	yes	yes
size()	yes	yes
resize()	yes	yes
capacity()	yes	no
reserve()	yes	no
max_size()	yes	yes
erase()	yes	yes
clear()	yes	yes
operator=	yes	yes
operator<	yes	yes
operator==	yes	yes
operator[]	yes	no
at()	yes	no
front()	yes	yes
back()	yes	yes
push_back()	yes	yes
pop_back()	yes	yes
assign()	yes	yes
insert()	yes	yes
swap()	yes	yes
push_front()	no	yes
pop_front()	no	yes
merge()	no	yes
remove()	no	yes
remove_if()	no	yes
reverse()	no	yes
sort()	no	yes
splice()	no	yes
unique()	no	yes

---

Links/Information:

• GNU String class - YoLinux Tutorial
• "Modest Tutorial"
• Technical University Vienna Tutorial
• Boost pointer container library - containter libraries (vectors,lists,maps,...) to hold pointers.
• An old fashioned linked list with pointers (old homework problem)
• GTK API:
  • Singly linked list API
  • Doubly linked list API