Chapter 7 Defining Your Own Date Types

第 7 章基本 C++ 程式碼整理如下

Reference: I Horton, Ivor Horton's Beginning Visual C++ 2013 (Wiley 2014).


7.1 The Struct in C++
∎ Struct
// Struct definition
struct Rectangle
{
    int left;
    int top;
    int right;
    int bottom;
};


7.2 Types, Classes, Objects, and Instances
∎ Class
// Definition of a class
class CBox
{
    public:
        double m_length; // Data members
        double m_width;
        double m_height;
};

∎ Class
// Main.cpp
CBox box1;  // Declare object box1 of type CBox
CBox box2;

if (box1 > box2)  // ">" is an operator acting on the objects
    box1.fill();  // "fill()" is a member function acting on object 1
else
    box2.fill();


7.3 Understanding Classes
∎ Accessing the data members of a class
// Main.cpp
CBox box1;
CBox box2;
box1.m_length = box1.m_width = box1.m_height = 2.0;
box2 = box1;  // Member-wise copying from box1 to box2

∎ Adding a member function to CBox
// Member function
double volume()
{
    return m_length * m_width * m_height;
}


7.4 Class Constructors
∎ Adding a Constructor to the CBox class  
// Constructor definition
CBox(double lv, double wv, double hv)
{
    cout << "Constructor called." << endl;
    m_length = lv;  // Set values of data members
    m_width = wv;
    m_height = hv;
}

∎ Default constructor
// Default constructor definition
CBox()
{
    cout << "Default constructor called." << endl;
}

∎ Constructor initialization list
// Constructor definition
CBox(double lv = 1.0, double wv = 1.0, double hv = 1.0) :
             m_length {lv}, m_width{wv}, m_height{hv}
{
    cout << "Constructor called." << endl;
}
cf. CCandyBox(double lv, double wv, double hv, const char* str = "Candy") :
             : CBox {lv, wv, hv}  // In the inherited class CCandyBox

∎ Making a constructor explicit 
// Make a constructor more specific, instead of generalCBox box;
box = 99.0;
CBox(double side) : m_Length {side}, m_Width {side}, m_Height {side}  {}  // Will compile
explicit CBox(double side) : m_Length {side}, m_Width {side}, m_Height {side} {}  // Will not, unless CBox box {4.0} is used 


7.5 Private Members of a Class
∎ Private data members
// CBox.h
class CBox
{
    private:
        double m_length;
        double m_width;
        double m_height;
};

// Main.cpp
box1.m_length = 4.0; // Error message: cannot access private data member declared in class CBox

∎ Friend function of a class
// Friend function prototype (in CBox.h) 
friend double boxSurface(const CBox& aBox);

// A function that is not a member of the class, but with special privilege
double boxSurface(const CBox& aBox)
{
    return 2.0 * (aBox.m_length * aBox.m_width + aBox.m_width * aBox.m_height
               + aBox.m_height * aBox.m_length); 
}

∎ Copying information between instances
// Initialize box2 with box1 (done by the default copy constructor)
CBox box2{box1};

// .h
CBox (const CBox& initB);

// .cpp
CBox::CBox(const CBox& initB):
            m_length{initB.m_length}, m_width{initB.m_width}, m_height{initB.m_height}


7.6 The Pointer This
∎ Explicit use of this
// main.cpp
if (cigar.compare(match))
    cout << "cigar is larger than match" << endl;
else
    cout << "cigar is not larger than match" << endl;

// .cpp
bool compare(CBox& aBox)
{
    return this->volume() > aBox.volume();
}



7.7 Const Objects
∎ Constant member functions of a class
// Non-const object
CBox cigar{8.0, 5.0, 1.0};
bool CBox::compare(CBox& aBox)

// const object
const CBox cigar{8.0, 5.0, 1.0};
bool CBox::compare(const CBox& aBox) const

∎ Member function definitions outside the class


7.8 Array of Objects


7.9 Static Members of a Class

∎ Counting instances of a class type (ex7_12)
static int objectCount;  // Count of objects in existence
int CBox:: objectCount{};  // Initialize static data member of CBox class; no keyword "static"


7.10 Pointers and References to Objects


7.11 Summary