·       The const Parameter Modifier

o      If you do not want a programmer to change the value of a parameter, use the const modifier before the parameter name.

o      The const Parameter modifier is usually used with Call-By-Reference (CBR) parameters for classes.

o      The const Parameter modifier is also good to use for very large parameters because it is more efficient than Call-By-Value (CBV). 

§       Remember, a CBV parameter is a local variable that is a copy of the function argument (thus, two copies are exist).

§       With CBR, the parameter is a placeholder that is replaced by the actual argument (thus, there is only one copy that exists).

// Example

 

// Declaration of a function to determine an

// elder person. Parameters are const CBR.

bool isOlder(const Person& P1, const Person& P2);

 

// Definition of a function to determine an

// elder person.  Parameters are const CBR.

bool isOlder(const Person& P1, const Person& P2)

{

     return (P1.getAge() > P2.getAge());

}

 

// Snippet of code from main()

Person A, B;

 

// Get all applicable information

A.getInformation();

B.getInformation();

 

// Check to see which person is older.

if(isOlder(A, B))

{

     A.displayName();

     cout << “ is older.\n”;

}

else

{

     B.displayName();

     cout << “ is older.\n”;

}

 

 

// A snippet of the class definition for Person.

class Person

{

public:

     …

     void getInformation();

     int getAge() const;

     void displayName() const;

     …

 

private:

     …

     string _fullName;

     int _age;

     …

};

 

 

// Implementation of the accessor function

// getAge().  Note: the use of the const

// modifier.

int Person::getAge() const

{

     return _age;

}

 

 

// Implementation of the member function

// displayName().  Note: the use of the const

// modifier.

void Person::displayName() const

{

     cout << _fullName;

}

 

 

 

 

 

 

// Summary of compiler results for Parameter types and

// argument types that are passed to a function that

// attempts to change the formal parameter.

 

Parameter and Argument	What Function Does	Compilation Result
CBV Parameter and argument passed is declared as const	Function tries to change Parameter	No Error.  Copy made to the formal parameter; hence, no change to declared const argument.
CBV Parameter and argument passed is not declared as const	Function tries to change Parameter	No Error.  There is nothing declared as const (parameter or argument).
CBR Parameter and argument passed is declared as const	Function tries to change Parameter	Error.  The Parameter is a placeholder for a const argument.
CBR Parameter and argument passed is not declared as const	Function tries to change Parameter	No Error.  There is nothing declared as const (parameter or argument).
const CBR Parameter and argument passed is declared as const	Function tries to change Parameter	Error.  Formal parameter is a const parameter
const CBR Parameter and argument passed is not declared as const	Function tries to change Parameter	Error.  Formal parameter is a const parameter

 

 

·       Inline functions

o      An inline function is a function that is preceded by the keyword inline.  It is treated special by the compiler in that the code is inserted at each location where the function is invoked.

o      An inline function is also a function whose full definition is given within the definition of a class.  It does not need to be preceded by the keyword inline.  It is treated in the same manner by the compiler.

o      An advantage of an inline function for smaller functions is that the code is more efficient.

o      A disadvantage of an inline function for very large functions is that the code is less efficient.

o      Another disadvantage is that it mixes the interface and implementation of a class.  This goes against the principal of encapsulation.

 

// Example

#include <iostream>

using namespace std;

 

class Person

{

public:

  void setAge(int age) { _age = age; }

  int getAge() const { return _age; }

 

private:

  int _age;

};

 

int main()

{

  Person A;

 

  A.setAge(50);

  cout << "The Age is " << A.getAge() << endl;

 

  return 0;

}

 

·       Static Members of a class

o      Static variables are variables that are declared static within a class definition.  The variable may be shared by all objects of the class.

§       Static variables are initialized outside of the class definition.  The keyword static is not used in the initialization; only in the class definition.

§       Static variables may be initialized only once.

o      Static functions are functions that are declared static within a class definition that are usually used to access static variables of the class.

§       Static functions are usually defined (implemented) outside of the class definition as most member functions are.  The keyword static is not used in the initialization; only in the declaration (prototype) that is within the class definition.

// Example

#include <iostream>

using namespace std;

 

class SomeObject

{

public:

   SomeObject() { objectCount++; }

   ~SomeObject() { objectCount--; }

  

   static int getObjectCount();

  

   void setNumber(int number) { _number = number; }

   int getNumber() const { return _number; }

 

private:

   static int objectCount;

   int _number;

};

 

int SomeObject::objectCount = 0;

 

int SomeObject::getObjectCount()

{

   return objectCount;

}

 

int main()

{

   SomeObject A, B, C, D, E, F, G, H, *I;

 

   D.setNumber(200);

   cout << "Object D number is set to " << D.getNumber() << endl;

 

   cout << "Total number of objects declared is "

          << SomeObject::getObjectCount() << endl;

 

   I = new SomeObject;

   cout << "Total number of objects declared is "

          << SomeObject::getObjectCount() << endl;

 

   delete I;

   cout << "Total number of objects declared is "

          << SomeObject::getObjectCount() << endl;

 

  

 

   return 0;

}

 

// Output

 

 

·       Vectors

o      Vectors serve the same purpose as arrays except that they can change length while the program is running.

o      Vectors are formed from a template class in the Standard Template Library (STL).

o      Vector elements are indexed starting at zero.  Square brackets may be used to access the elements provided the element has memory allocated for it.

o      A Vector has a base type and stores a collection of values of its base type.

 

//Example

#include <iostream>

#include <vector>

using namespace std;

 

int main()

{

      vector<int> a, b(5), c;

      int i;

 

      // Vector ‘a’ must be initialized using push_back();

      a.push_back(4);

      a.push_back(3);

      a.push_back(2);

      a.push_back(1);

      a.push_back(5000);

 

      // We can use [] on ‘b’, but not on ‘a’ or a runtime error will

// occur.

      for(i = 0; i < 5; i++)

            b[i] = i;

 

      // We can add to ‘b’ further using push_back();

      b.push_back(10000);

 

 

      // We can set vector ‘c’

      c = a;

 

      cout << "The Current Arrays:\n\n";

 

      cout << "The A vector:\n";

      for(i = 0; i < a.size(); i++)

            cout << a[i] << endl;

 

      cout << "The B vector:\n";

      for(i = 0; i < b.size(); i++)

            cout << b[i] << endl;

 

      cout << "The C vector:\n";

      for(i = 0; i < c.size(); i++)

            cout << c[i] << endl;

 

      return 0;

}

 

// Output

 

 

 

 

 

 

// Some useful member functions:

Member Function	Description
push_back(arg)	Adds an element that is the same type as arg.  Starts at position 0, then 1, 2, 3, etc …
size()	Returns the number of vector elements.
capacity()	Returns the amount of capacity allocated for the vector elements.  This is greater than or equal to size().
reserve(number)	Allows you to set the capacity of the vector to number elements.  This function cannot decrease the size of the vector; only increase.
resize(number)	Allows you to resize the vector to number elements.  If the current size is less than number, new elements are added and initialized according to the appropriate constructor.  If the current size is greater than number, the elements that are higher than number are removed.