Constructor

[Ducky]

Hi!

Does a constructor of a class get called even before the program gets in main()?

Im asking this because i have a program where the function associated with the constructor isnt called in main() but the function was called despite of it.

I post only the relevant parts for simplicity.

class Socket
{
    protected:
        WSADATA     wsaData;
        
    public:
        Socket();
        ~Socket();
};

Socket::Socket()
{
    if( WSAStartup( MAKEWORD(2, 2), &wsaData ) != NO_ERROR )
    {
        cerr << "Socket Initialization: Error with WSAStartup\n";
        system("pause");
        WSACleanup();
        exit(10);
    }

    //Create a socket
    mySocket = socket( AF_INET, SOCK_STREAM, IPPROTO_TCP );

    if ( mySocket == INVALID_SOCKET )
    {
        cerr << "Socket Initialization: Error creating socket" << endl;
        system("pause");
        WSACleanup();
        exit(11);
    }
}
 
class ClientSocket : public Socket  //Inheritance
{
    public:
        void ConnectToServer( const char *ipAddress, int port );
};

void ClientSocket::ConnectToServer( const char *ipAddress, int port )
{
    sockad.sin_family = AF_INET;
    sockad.sin_addr.s_addr = inet_addr( ipAddress );
    sockad.sin_port = htons( port );

    cout << "CONNECTED.\n\n";

    if ( connect( mySocket, (SOCKADDR*) &sockad, sizeof( sockad ) ) == SOCKET_ERROR )
    {
        cerr << "ClientSocket: Failed to connect\n";
        system("pause");
        WSACleanup();
        exit(13);
    }
}
int main()
{
    string choice;
    int port = 666;
    //char *ipAddress = "127.0.0.1";
    string ipAddress;
    char recMessage[STRLEN] = {0};
    while(1){
    cout << "1) Client" << endl;
    cout << "2) Server" << endl;
    cin  >> choice;

    /***************************************CLIENT***************************************/
    if ( choice == "1" )
    {
        cout << "Enter IP address of server:" << endl;
        cin >> ipAddress;
        ClientSocket sockClient;
        cout << "ATTEMPTING TO CONNECT..." << endl;
        sockClient.ConnectToServer( ipAddress.c_str(), port );        
...etc

[laserlight]

What on earth is a ClientSocket? I guess that it is a derived class of Socket, in which case the Socket default constructor is likely invoked at this point in the global main function:

ClientSocket sockClient;

[RockyMarrone]

I think ClientSocket is derived from Socket class,
In that case
from main the constructor[of Socket] will be called in this line ClientSocket sockClient;

[RockyMarrone]

See Ducy constructor in C++ will be called from Base to Child and Destructor will be called from Child to Base class thats why from the ClientSocket sockClient; line it is getting called

[Ducky]

Yes it is a derived class, i added it to the code above.

So when you call the derived class it will automatically invoke the constructor in the base class.

Ok thank you very much i understand it now.

[Ducky]

"See Ducky constructor in C++ will be called from Base to Child and Destructor will be called from Child to Base class thats why from the ClientSocket sockClient; line it is getting called"

Dont you mean the contrary?

constructor invoked from Child to Base class?

And when you dont have a Child its when you call the method or the data in the class when the
constructor gets called?

[RockyMarrone]

See Ducky the Concept of class is very very simple


Class provides u a way to define some functions which will play on some data.

Ok.


Class constructor is always gets called when u instantiate an object of that class.


I will give u an example lets say

class Base { 
public: 
  Base() { printf("Base\n"); } 
};

class Child : public Base {
public: 
  Child() { printf("Child\n"); } 
};

class Child1 : public Child {
public: 
  Child1() { printf("Child1\n"); } 
};

int main() {
  Child1 c1; 
  // Out put will be like this 
  //  For Constructor it 
  Base
  Child
  Child1

  //  For Destructor it 
  Child1
  Child
  Base

  return 0;
}

And if u dont have any inheritance involved then

class ABC {
public:
  ABC() {
    printf("ABC\n");
  }
};

int main() {
  ABC obj; // constructor will be called
  ABC ptr_obj = new ABC(); // constructor will be called
  return 0;
}

[Ducky]

Ah ok i get it, its really simple indeed.

Thanks a lot for the explanation Rocky, that was nice from you.