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    Lecture 7

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    Ayesha Hussain
    The document discusses various concepts in C++ related to object-oriented programming including static members, const members, and mutable members. Static members allow data to be shared across all objects of a class. Const members ensure objects and member functions do not modify object data. Mutable members allow specific data members of const objects to be modified.

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    Lecture 7

    Uploaded by

    Ayesha Hussain
    16 views18 pages
    The document discusses various concepts in C++ related to object-oriented programming including static members, const members, and mutable members. Static members allow data to be shared across all objects of a class. Const members ensure objects and member functions do not modify object data. Mutable members allow specific data members of const objects to be modified.

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    Lecture-7

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    The document discusses various concepts in C++ related to object-oriented programming including static members, const members, and mutable members. Static members allow data to be shared across all objects of a class. Const members ensure objects and member functions do not modify object data. Mutable members allow specific data members of const objects to be modified.

    Copyright:

    © All Rights Reserved
    Download as PPT, PDF, TXT or read online from Scribd
    Download as ppt, pdf, or txt
    16 views18 pages

    Lecture 7

    Uploaded by

    Ayesha Hussain
    The document discusses various concepts in C++ related to object-oriented programming including static members, const members, and mutable members. Static members allow data to be shared across all objects of a class. Const members ensure objects and member functions do not modify object data. Mutable members allow specific data members of const objects to be modified.

    Copyright:

    © All Rights Reserved
    Download as PPT, PDF, TXT or read online from Scribd
    Download as ppt, pdf, or txt
    of 18

    CS-212

    OBJECT ORIENTED
    PROGRAMMING
    MEHREEN TAHIR
    Quiz 3
    #include <iostream>
    void populate_array(int *array, int N){
    for (int i=0;i<N;i++){
    std::cin>>array[i];
    }
    }
    void print_array(int *array, int N){
    for (int i=0;i<N;i++){
    std::cout<<array[i]<<std::endl;
    }
    }
    int main() {
    int *a=new int[5];
    populate_array(a,5);
    print_array(a,5);
    }
    #include <iostream>
    class Box{
    private:
    int l,w,h;
    int *a;
    public:
    Box()
    {l=w=h=0;
    a=new int[2];
    *a=5;
    *(a+1)=8;}
    Box(Box &b)
    {l=b.l;h=b.h;w=b.w;
    // a=b.a;
    a=new int[2];
    *a=*(b.a);
    *(a+1)=*((b.a)+1);}
    void setarr(int x,int y){
    *a=x;
    *(a+1)=y;}
    void getarr(){
    std::cout<<*a;
    std::cout<<*(a+1);}
    };
    int main()
    { Box b;
    Box x(b);
    //Box z=b;
    // z.getarr();
    b.setarr(9,19);
    b.getarr();
    x.getarr();
    }
    Common Data
    • What to do if you want to have some data
    common or shared across ALL objects in a
    class?
    • For example, total number of students
    Scope of Variables
    • Life time of a variable in a program
    • Local variables
    • Global variables
    Static members
    • To solve this issue we can create a static
    variable and give it an initial value.
    • The initialization is performed only the first
    time the function is called ,and the data
    retains its value between function calls. This
    way, a function can “remember” some piece
    of information between function calls.
    Static members
    • No matter how many objects of the class are
    created, there is only one copy of the static
    member
    • A static member is shared by all objects of the
    class
    Scope of static members
    • Class scope
    • Lifetime: entire program
    • It exists without object
    Static functions
    • Static member functions can only access static
    data members
    • Non-static methods can access both static and
    non-static data members.
    Static members
    • Static class variables (or data members)
    • “Class-wide” data
    • Property of class, not specific to object of class
    • Efficient when single copy of data is enough
    • It mainly represents the shared data
    • Only the static variable has to be updated
    • Only accessible to objects of same class
    Static members
    • Initialized exactly once in the class
    Implementation file
    • Exist even if no objects of class exist
    • Lifespan: program START to program END
    • Can be public , private or protected
    const
    • C++ introduces the concept of a named
    constant that is just like a variable , except
    that its value cannot be changed.
    • const data members must be initialized using
    member initializer list
    const Member function
    • A const member function guarantees that it
    will never modify any of its data.
    • Candidates for being made const because
    they don’t need to modify any data.
    • Member functions that do nothing but acquire
    data from an object are obvious candidates
    for being made const because they don’t need
    to modify any data.
    const Member function
    • Any const member function that attempts to
    change a member variable or call a non-const
    member function will cause a compiler error
    to occur.
    • Constructors and destructors cannot be const
    Mutable Data
    • With const object you want to alter some data
    Mutable Data
    • The keyword mutable is mainly used to allow
    a particular data member of const object to
    be modified.
    • Adding mutable to a variable allows a const
    pointer to change members.
    • mutable is particularly useful if most of the
    members should be constant but a few need
    to be updatable.
    Mutable Data
    • Data members declared as mutable can be
    modified even though they are the part of
    object declared as const.
    • You cannot use the mutable specifier with
    names declared as static or const, or
    reference.
    Mutable Data
    #include <iostream>
    class Mutable
    {
    public:
    Mutable(){
    val=0;
    val1=0;
    }
    public:
    mutable int val;
    int val1;
    };
    int main() {
    const Mutable m;
    m.val=9;
    // m.val1=6; // This line will throw an error because const objects cannot be modified. But mutable forces the object to modify itself
    std::cout<< m.val;
    return 0;
    }

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