c构造函数和析构函数

Program 1:

程序1：

#include<iostream>
using namespace std;
class Sample
{
private:
int X;
int Y;
public:
Sample(int x, int y)
{
X = x;
Y = y;
}
void set(int x, int y)
{
X = x;
Y = y;
}
void print()
{
cout<<X<<" "<<Y<<endl;
}
};
int main()
{		
Sample S[2];
Sample *PTR;
PTR = S;
PTR[0].set(10,20);
PTR[1].set(30,40);
PTR[0].print();
PTR[1].print();
return 0;
}

Output:

输出：

main.cpp: In function ‘int main()’:
main.cpp:32:12: error: no matching function for call to ‘Sample::Sample()’
Sample S[2];

Explanation:

说明：

The above code will generate a syntax error because in the main() function we created an array of objects that must be instantiated by the default constructor, but in the class, the default constructor is not defined.

上面的代码将产生语法错误，因为在main()函数中，我们创建了必须由默认构造函数实例化的对象数组 ，但是在类中，未定义默认构造函数。

Program 2:

程式2：

#include <iostream>
using namespace std;
class Sample {
private:
int X;
int Y;
public:
Sample(int x, int y)
{
X = x;
Y = y;
}
void set(int x, int y)
{
X = x;
Y = y;
}
void print()
{
cout << X << " " << Y << endl;
}
};
int main()
{
Sample S[2] = { Sample(0, 0), Sample(0, 0) };
Sample* PTR;
PTR = S;
PTR[0].set(10, 20);
PTR[1].set(30, 40);
PTR[0].print();
PTR[1].print();
return 0;
}

Output:

输出：

10 20
30 40

Explanation:

说明：

In the above program, we created a class Sample that contains two data members X and Y, one parameterized constructor, set() and print() member functions. 

在上面的程序中，我们创建了一个Sample类，其中包含两个数据成员 X和Y ，一个参数化的构造函数 ， set()和print()成员函数。

Now coming to the main() function, we created an array of objects and that will instantiated by the parameterized constructor. And created a pointer that is being initialized with the base address of array objects. And then called set() and print() functions using the pointer.

现在进入main()函数，我们创建了一个对象数组，该数组将由参数化构造函数实例化。 并创建了一个使用数组对象的基地址初始化的指针。 然后使用指针调用set()和print()函数。

Program 3:

程式3：

#include <iostream>
using namespace std;
class Sample {
private:
int X;
public:
Sample() const
{
}
void set(int x)
{
X = x;
}
void print()
{
cout << X << endl;
}
};
int main()
{
Sample S;
S.set(10);
S.print();
return 0;
}

Output:

输出：

main.cpp:9:14: error: constructors may not be cv-qualified
Sample() const
^~~~~

Explanation:

说明：

The above program will generate an error because we cannot create a constructor as a const member function in C++.

上面的程序将产生错误，因为我们不能在C ++中将构造函数创建为const成员函数。

翻译自: https://www.includehelp.com/cpp-tutorial/constructor-and-destructor-find-output-programs-set-2.aspx

c构造函数和析构函数