в 14:21, 25 мая 2010

2010-05-25T14:21:17Z

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2010-05-25T10:29:26Z

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==A simple constructor and destructor.==

<source lang="cpp">#include <iostream>
using namespace std;

class MyClass {
public:
int x;

MyClass(); // constructor
~MyClass(); // destructor
};

// Implement MyClass constructor.
MyClass::MyClass() {
x = 10;
}

// Implement MyClass destructor.
MyClass::~MyClass() {
cout << "Destructing...\n";
}

int main() {
MyClass ob1;
MyClass ob2;

cout << ob1.x << " " << ob2.x << "\n";

return 0;
}</source>
<pre class=codeResult>10 10
Destructing...
Destructing...</pre>

==Close stream in destructor==

<source lang="cpp">#include <fstream>
#include <iostream>
using namespace std;
class MyClass
{
private:
char msg[20];
int loopcounter;
fstream myfile;

public:
void display();
MyClass();
~MyClass();
};
MyClass::MyClass()
{
myfile.open("input.txt",ios::in);
myfile.getline(msg,20);
}
MyClass::~MyClass()
{
myfile.close();
}
void MyClass::display()
{
cout << msg << "\n";
}
int main() {
MyClass obj;
obj.display();
return 0;
}</source>

==Demonstrating the order in which constructors and destructors are called.==

<source lang="cpp">#include <string>
#include <iostream>
using std::string;
using std::cout;
using std::endl;
class MyClass
{
public:
MyClass( int, string ); // constructor
~MyClass(); // destructor
private:
int objectID;
string message;
};
MyClass::MyClass( int ID, string s )
{
objectID = ID;
message = s;
cout << "Object " << objectID << " constructor runs " << message << endl;
}
MyClass::~MyClass()
{
cout << "Object " << objectID << " destructor runs " << message << endl;
}
void create( void );
MyClass first( 1, "(global before main)" );
int main()
{
MyClass second( 2, "(local automatic in main)" );
static MyClass third( 3, "(local static in main)" );

create(); // call function to create objects
MyClass fourth( 4, "(local automatic in main)" );
return 0;
}
void create( void )
{
cout << "\nCREATE FUNCTION: EXECUTION BEGINS" << endl;
MyClass fifth( 5, "(local automatic in create)" );
static MyClass sixth( 6, "(local static in create)" );
cout << "\nCREATE FUNCTION: EXECUTION ENDS" << endl;
}</source>
<pre class=codeResult>Object 1 constructor runs (global before main)
Object 2 constructor runs (local automatic in main)
Object 3 constructor runs (local static in main)
CREATE FUNCTION: EXECUTION BEGINS
Object 5 constructor runs (local automatic in create)
Object 6 constructor runs (local static in create)
CREATE FUNCTION: EXECUTION ENDS
Object 5 destructor runs (local automatic in create)
Object 4 constructor runs (local automatic in main)
Object 4 destructor runs (local automatic in main)
Object 2 destructor runs (local automatic in main)
Object 6 destructor runs (local static in create)
Object 3 destructor runs (local static in main)
Object 1 destructor runs (global before main)</pre>

==virtual destructor methods==

<source lang="cpp">#include <iostream>

class Animal
{
public:
Animal():itsAge(1) { std::cout << "Animal constructor...\n"; }
virtual ~Animal() { std::cout << "Animal destructor...\n"; }
virtual void Speak() const { std::cout << "Animal speak!\n"; }
protected:
int itsAge;
};

class Cat: public Animal
{
public:
Cat() { std::cout << "Cat constructor...\n"; }
~Cat() { std::cout << "Cat destructor...\n"; }
void Speak()const { std::cout << "Meow!\n"; }
};

int main()
{
Animal *pCat = new Cat;
pCat->Speak();
return 0;
}</source>
<pre class=codeResult>Animal constructor...
Cat constructor...
Meow!</pre>

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в 14:21, 25 мая 2010

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