一般的我们喜欢这样对对象赋值：
Person p1;Person p2=p1;
classT object(another_object), or A a(b);
classT object = another object;
class A
{
// …
};
int main( )
{
A x;
A y(x);
// …
A z = x;
z = y;
}
这样的话，如果成员变量中有指针的话，就容易造成指针的二次删除。这样就需要我们显示的在类中实现
1、拷贝构造，
2、赋值运算符重载。
1）、判断是不是自赋值，2）、释放旧空间，3）、开辟新空间。4）、内容本身的 拷贝，5）、返回*this
3、析构函数（释放指针指向的空间）。
这三步使类实现深拷贝，从而避免浅拷贝的二次删除问题。俗称三大件。
class Vector
{
private:
int *rep;
int size;
void clone(const Vector& a);
void dispose( );
public:
Vector(int s=0);
// a default constructor initializing all members of rep to 0 if s is not 0.
Vector( int*, int );
// a constructor creates a Vector object from an ordinary array
Vector(const Vector& v);
// a copy constructor
~Vector( ) {dispose( );} // a destructor
int get_size( ) const {return size;} // an accessor
const Vector& operator=(const Vector& x);
int& operator[ ](int index) {return rep[index];}
const int& operator[ ](int index) const {return rep[index];}
};
//Vector v;
//V = a;
//Vector v(a);
void Vector::clone(const Vector& a)
{
this->size = a.size; rep = new int[size];
for (int count = 0; count < size; ++count)
rep[count] = a[count]; // (*this)[count] = a[count];
// rep[count] = a.rep[count];
}
void Vector::dispose( )
{
delete [ ] rep;
rep = NULL;
}
Vector::Vector(int s) : size(s)
{
if (size <= 0)
{ rep = NULL; }
else
{
rep = new int[size];
for (int count = 0; count < size; ++count)
{ rep[count] = 0; } }
}
Vector::Vector(int* a, int s) : size(s), rep(new int[s])
{
for (int count = 0; count < size; ++count)
{ rep[count] = a[count]; }
}
Vector::Vector(const Vector& v)
{ clone(v); }
//for example: Vector a, v; a.=(v);
const Vector& Vector::operator=(const Vector& x)
{
if ( this != &x ) //Vector v; Vector* p = &v; v = *p;
{
delete []rep;
this->size = x.size;
rep = new int[size];
for (int count = 0; count < size; ++count)
rep[count] = x[count];
}
return *this;
}
// overloading operator <<, not a friend function
ostream& operator<<(ostream& out, const Vector& x)
{
int s = x.get_size( );
for (int i = 0; i < s; ++i)
{
out << x[i]<<endl; // out<<x.rep[i]<<endl;
}
out << endl;
return out;
}
bool operator==(const Vector& a, const Vector& b)
{
bool yes = true;
if (a.get_size( ) != b.get_size( ))
{ yes = false; }
else
{
int s, index = 0;
s = a.get_size( );
while (index < s && a[index] == b[index])
{ ++index; }
if (index < s)
{ yes = false; }
}
return yes;
}
int main()
{
Vecter vec1;
cout<<vec1<<endl;
int array[5] = {1,2,3,4,5};
Vector vec2( array, 5 );
cout<<vec2<<endl;
Vector vec3( vec2 );
cout<<vec3<<end;
if( vec3 == vec2 )
{
Cout<<”The vector3 is equal to vector2”<<endl;
}
Vector vec4;
vec4 = vec3;
cout<<vec4<<end;
return 0;
}